12. Biosignaling

7/24/2019 12. Biosignaling

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MC LC

MU................................................................................................................................................ 2

12.1 CC C CHPHN TCA STRUYN TN HIU....................................................... 3

12.2 CC KNH ION C CNG....................................................................................................... 8

12.3 CC RECEPTOR ENZYME.................................................................................................... 15

12.4 CC RECEPTOR LIN KT VI PROTEIN G V CC CHT TRUYN TIN THHAI....................................................................................................................................................... 28

12.5 CC PROTEIN NNG A HNH V CC MNG MNG......................................... 50

12.6 STRUYN TN HIU VI SINH VT V THC VT................................................. 57

12.7 STRUYN CM GIC TRONG NHN, NGI, NM...................................................... 65

12.8 IU HA PHIN M NHCC HORMONE STEROID................................................ 79

12.9 IU HA CHU KTBO BI CC PROTEIN KINASE............................................ 82

12.10 CC GEN GY UNG TH, CC GEN C CHKHI U V CHT THEO CHNGTRNH CA TBO........................................................................................................................ 90

TI LIU THAM KHO................................................................................................................ 106


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MUKhi ti ln u tin i vo nghin cu hot ng ca hormone, cch y 25 nm,

c mt cm gic lan rng gia nhng nh sinh hc m hot ng hormone khng thc nghin cu mt cch c ngha trong shin din ca cu trc tbo c t

chc. Tuy nhin, khi ti suy ngh vlch sca sinh ha hc, n dng nh gi choti c mt khnng thc srng cc hormone c thhot ng mc phn t.

-Erl W. Sutherland, Nobel Address, 1971

Khnng ca cc tbo nhn v hot ng nhcc tn hiu tmng plasmal nn tng i vi ssng. Cc tbo vi khun thng xuyn nhn tn hiu u vokhng i tcc protein mng hot ng nh cc thththng tin,tmi trng xungquanh vi pH, lc thm thu, thc n c sn, oxygen v nh sng, v sc mt ca

cc cht ha hc c hi, ng vt n tht, hay cc cht cnh tranh vi thc n. Cc tnhiu ny to ra cc p ng thch hp, nh l svn chuyn hng ti thc n, haytrnh xa cc c cht c hi hoc hnh thnh cc bo t ng trong mt mi trngkhng c cht dinh dng. cc sinh vt a bo, cc tbo vi cc chc nng khcnhau trao i mt lot cc tn hiu. Cc tbo thc vt p ng vi cc hormone tngtrng v vi nhng bin i di nh sng mt tri. Cc tbo ng vt trao ithng tin v cc nng ca cc ion v glucose trong cc dch ngoi bo, cc hotng chuyn ha ph thuc ln nhau xy ra trong cc m khc nhau, v trong mt

phi, sthay thng ca cc tbo trong sut qu trnh pht trin. Trong tt ccc

trng hp ny, tn hiu biu hin thng tin c pht hin bi cc ththchuyn bitv c chuyn thnh mt p ng tbo, lun lun i hi mt qu trnh ha hc.S chuyn i thng tin thnh mt thay i ha hc, s truyn tn hiu, l mt ctnh chung ca cc tbo sng.

Slng cc tn hiu sinh hc khc nhau th ln ( Bng 12-1), nh l nhiu png sinh hc khc nhau vi cc tn hiu ny, nhng cc sinh vt sdng chmt t ccc chbo tn tin ha pht hin cc tn hiu ngoi bo v chuyn chng thnhnhng thay i ni bo. Trong chng ny chng ti kim tra mt sv dvnhiu

lp c ch truyn tn hiu, hy nhn vo cch chng ti kt hp cc chc nng sinhhc chuyn bit nh l struyn cc tn hiu thn kinh; p ng vi cc hormone vcc nhn ttng trng; gic quan nhn, ngi, v nm v kim sot chu trnh tbo.Thng thng, kt qucui cng ca con ng truyn tn hiu l sphosphoryl haca mt sprotein tbo ch chuyn bit, thay i cc hot ng ca chng v do lm thay i cc hot ng ca tbo. Thng qua cuc tho lun ca chng ti chngti nhn mnh sbo tn ca cc c chc bn cho struyn cc tn hiu sinh hc vs thch nghi ca cc c ch ny vi mt vng rng ca cc con ng truyn tnhiu.


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Bng 12-1. Mt stn hiu m cc tbo p ng

12.1 CC C CHPHN TCA STRUYN TN HIU

Nhng s truyn tn hiu kh chuyn bit v cc k nhy. Tnh c hiu tc bng sbsung phn tchuyn bit gia cc phn ttn hiu v receptor (Hnh12-1a.) qua trung gian bi cc loi lin kt yu tng tnhau ( khng phi lin ktcng ha tr) qua trung gian cc tng tc enzyme-c cht v khng nguyn-khngth. Sinh vt a bo c mt mc c hiu cao hn, bi v cc receptor nhn mt tnhiu no , hoc cc receptor ch ni bo ca mt ng truyn tn hiu nht nh,

ch c trong mt vi loi t bo nht nh. Cho v d, hormone phng thchThyrotropin c phn ng nhanh trong cc t bo ca thy trc tuyn yn nhngkhng c phn ng g trong cc tbo gan, m thiu cc receptor cho hormoneny. Epinephrine lm thay i s chuyn ha glycogen trong cc t bo gan nhngkhng lm thay i schuyn ha glycogen trong cc tbo hng cu; trong trnghp ny, chai loi tbo c cc receptor cho hormone, trong khi cc tbo gan chaglycogen v cc enzyme chuyn ha glycogen c kch thch bi epinephrine, cc t

bo hng cu th khng cha glycogen v cc enzyme chuyn ha glycogen.

Ba yu t to ra nhy cao ca cc cht truyn tn hiu: i lc cao ca ccreceptor vi cc phn t tn hiu, shp tc (thng xuyn, nhng khng phi lunlun) trong stng tc ligand - receptor, v skhuch i ca tn hiu bi cc thcenzyme ( enzyme cascade). i lc gia ligand v receptor c thc biu hin nhl hng sphn lyKd, thng l 10-10M hay t hn - c ngha l receptorpht hin ccnng mt phn t (picomolar) ca mt phn t tn hiu. Cc tng tc receptor-ligand c nh lng bng phn tch Scatchard, mang li mt thc o nh lngi lc (Kd) v slng cc vng lin kt vi ligand trong mt mu thth(Khung 12-1).


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Hnh 12.1. Bn c im ca hthng truyn tn hiu

Tnh hp tc trong tng tc receptor - ligand dn n nhng thay i ln trongshot ha receptor vi nhng thay i nhtrong nng ligand (nhli nh hngca shp tc da trn lin kt oxygen vi hemoglobin; xem hnh. 5-12). Skhuchi bi cc thc enzyme l kt qukhi mt enzyme lin kt vi mt receptor tn hiuc hot ha v ngc li, xc tc shot ha ca nhiu phn tca mt enzyme

thhai, mi phn t trong s hot ha nhiu phn tca mt enzyme thba, vtip tc nhvy (Hnh. 12-1b). Cc thc nhvy c thto ra nhng skhuych imt vi mc cng trong vi mili giy.

nhy ca cc hthng receptor phthuc vo sci bin. Khi mt tn hiuxut hin lin tc, kt qul tnh nhy ca hthng receptor bgim i (Hnh. 12-1c);khi kch thch gim xung di mt ngng nht nh, hthng mt ln na trnnnhy. Hy suy ngh vnhng g xy ra vi hthng dn truyn thgic ca bn khi

bn i btdi tri nng chi chang vo mt cn phng ti hoc tbng ti ra nh

sng.Mt tnh nng ng ch cui cng ca cc hthng truyn tn hiu l stch

hp (Hnh. 12-1d), khnng ca hthng nhn c nhiu tn hiu v to ra mtp ng ph hp vi nhu cu ca tbo hoc sinh vt. Cc con ng truyn tn hiukhc nhau tng tc vi nhau nhiu mc , to ra nhiu tng tc duy tr cn bngni mi trong tbo v sinh vt.


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Khung 12-1 Thc nghim ha sinhPhn tch Scatchard nh lng stng tc Receptor - LigandCc hot ng t bo ca mt hormone

bt u khi hormone ( Ligand, L) lin ktc hiu v cht chvi protein receptor( R) ca n trn hoc trong tbo ch.Lin kt qua trung gian cc tng tckhng cng ha tr ( hydrogenbonding,hydrophobic v electrostatic) gia cc bmt b sung ca ligand v receptor.Tng tc receptor ligand lm thay ihnh thdo lm thay i hot tnh sinhhc ca receptor m c th l mt

enzyme, mt tc nhn iu ha enzyme,mt knh ion hay mt tc nhn iu hasbiu hin gen.Lin kt receptorligand c m tbi

phng trnh:

Lin kt ny ging nh l ca mtenzyme vi c cht ca n, ph thucvo cc nng ca cc thnh phntng tc v c th c m t bi mthng scn bng:

Trong , Kal hng slin kt vKdlhng sphn ly.Ging nh lin kt enzyme - c cht,lin kt receptorligand c tnh bo ha.Khi thm nhiu ligand vo mt sreceptor cnh, mt phn on tng lnca cc phn treceptor bchim chbiligand ( Hnh 1a). Mt phng php o ilc receptor ligand c ghi nhn bisbsung nng ca ligand cn ghinhn phn na s bo ha ca receptor.

Nh s dng phn tch Scatchard calin kt receptorligand m chng ti cth tnh c hng s phn ly Kd v svng gn vi receptor. Khi lin kt tn trng thi cn bng, tng svng gnc th,Bmax, cn bng vi svng khng

T dng th c mt phn b chn caphng trnh, chng ta c ththy mt thca tl[ligand lin kt/ ligand tdo]

vi [ ligand lin kt] nn l mt ngthng vi dcKa( -1/Kd) v mt phnng thng bchn trn ta caBmax,tng s vng lin kt ( Hnh 1b). Cctng tc hormone ligand c cc gi tr

Kd in hnh t 10-9 n 10-10 M, tngquan vi lin kt rt cht.Phn tch Scatchard th ng tin cy chocc trng hp n gin nht, nhng khivi cc thLinewweaver-Burk cho cc

enzyme, khi receptor l mt protein dlpth, cc thkhng cn tuyn tnh na.

Hnh 1 Phn tch Scatchard ca mt tngtc receptor ligand. Cho v d, mt ligand(L) c nh du phng x - mt hormoneti mt snng c thm vo mt lngreceptor ( R) c nh, v tiu phn cahormone lin kt vi receptor c xc nh

bng cch phn tch phc hp receptor hormone ( RL) thormone tdo. (a) Mt

th ca t l [RL] vi [L] + [R] ( hormonetng s c thm vo) l ng hyperbol,tng theo hng [RL] ti a khi cc vng


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gn, biu thbi [R], cng thm svnggn vi ligand, [RL]; l: Bmax= [R] +[RL]. S vng khng gn c th c

biu din theo tng s vng tr i svng gn: [R] = Bmax [RL]. Biu thccn bng c thc vit nh sau:

S ti sp xp cha t l ca ligand gnvi receptor v ligand khng gn vireceptor chng ta c:

receptor tr nn bo ha. kim sot skhng bo ha, cc vng lin kt khng chiu ( cho v d, cc hormone eicosanoid linkt khng c hiu vi lp i lipid ), mtchui cc th nghim lin kt c phn tch

th cng cn thit. Mt s tng vt qu cahormone c nh du c thm vo vidung dch hormone c nh du pha long.Cc phn tkhng nh du cnh tranh vicc phn t c nh du gn c hiuvi vng bo ha trn receptor, nhng gnkhng c hiu vi vng ny. Gi tr ngcho lin kt c hiu th t c bi t stri lin kt khng c hiu tlin kt tng.(b) Mt th tuyn tnh ca t l [RL]/[L]vi [RL] cKdvBmaxcho phc hp receptor

hormone. So snh cc thny vi cc thca tlVo vi [S] v 1/Vo vi 1/[S] cho

phc hp enzyme c cht ( xem hnh 6-12,khung 6-1).

y, chng tiquan tm n cc chi tit phn tca mt shthng truyntn hiu tiu biu. Vic hot ha cho mi h thng l khc nhau, nhng nhng cim chung ca struyn tn hiu th chung cho tt c: mt tn hiu tng tc vi mtreceptor; receptor c hot ha tng tc vi bmy tbo, to ra mt tn hiuthhai hay mt thay i trong hot ng ca mt protein tbo; hot ng chuyn

ha (nh ngha mrng l bao gm schuyn ha ca RNA, DNA, v protein) catbo ch tri qua mt sthay i; v cui cng, sdn truyn kt thc v tbo trli trng thi ban u cha c hot ha. minh ha cho cc c tnh chung cacc h thng truyn tn hiu, chng ti cung cp cc v dv su c ch truyn tnhiu cbn (Hnh. 12-2).

1. Cc knh ion c cng ca mng plasma m v ng (do c thut ng"gating") trong p ng vi s lin kt ca cc tn hiu ha hc hay cc thayi trong in thxuyn mng. y l cc cht truyn tn hiu n gin nht.

Knh ion receptor acetylcholine l mt v dvcchny (Mc 12.2).2. Cc receptor enzyme, cc receptor mng plasma cng l cc enzym. Khi mt

trong nhng receptor ny c hot ha bi ligand ngoi bo, n xc tc snxut mt cht truyn tin th hai ni bo Mt v d l receptor insulin (Mc12.3).

3. Cc receptor protein ( cc receptor rn ) hot ha gin tip ( thng qua ccprotein lin kt GTP hoc cc protein G ) cc enzyme to ra cc cht truyn tinthhai ni bo. iu ny c minh ha bi h thng -adrenergic receptor

pht hin epinephrine (adrenaline) (mc 12.4).

4.

Cc receptor nhn ( steroid receptors) khi lin kt vi tn hiu chuyn bit cachng (chng hn nhhormone estrogen), thay i tc ( mc biu hin


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gen) m ti cc gen c hiu c phin m v dch m thnh cc protein tbo. Bi v cc hormon steroid thc hin chc nng ca n thng qua cc cchlin quan mt thit n siu ha biu hin gen, y chng ti chvitngn gn vhot ng ca cc hormone ny (Mc 12.8) v stho lun chi tit

hn Chng 28.5. Cc receptor thiu hot tnh enzyme nhng thu ht v hot ha cc enzym t

bo cht tc ng ln cc protein xui dng ( downstream proteins), hoc bngschuyn i trc tip cc enzyme thnh cc protein iu ha gen hoc bngcch hot ha mt thc ca cc enzyme m cui cng hot ha mt tc nhniu ha gen. Hthng JAK-STAT minh ha cchu tin (Phn 12.3); vhthng truyn tn hiu TLR4 (Toll) thhai trn ngi (Mc 12.6).

6. Cc receptor ( cc receptor bm dnh) tng tc vi cc thnh phn i phn tca cht nn ngoi bo (nhcollagen) v truyn n hthng bxng tbo

da trn sdi ng tbo hoc bm cht vo cht nn ( matrix) . Cc integrin(tho lun trong Chng 10) minh ha tnh chung ny ca cchdn truyn.

Hnh 12-2. Su nhn ttruyn tn hiu chung

Nhchng ta thy, struyn tn hiu ca tt csu cchphbin cn c shot ha cc protein kinase, enzyme vn chuyn mt nhm phosphoryl tATP chomt chui bn protein.


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TM TT 12.1

Tt ccc tbo c cc c chtruyn tn hiu chuyn bit v nhy cao c botn trong sut qu trnh tin ha.

Nhiu tc nhn kch thch khc nhau, bao gm cc hormone, cc cht dn truynthn kinh, v cc yu t tng trng, hot ng thng qua cc protein receptor chiu trong mng plasma.

Cc receptorlin kt vi phn ttn hiu, khuch i tn hiu, tch hp tn hiu uvo tcc receptor khc, v truyn ti n vo trong tbo. Nu cc tn hiu vn cn,tnh nhy ca receptor gim hoc kt thc phn ng.

Cc tbo nhn chun c su c chtruyn tn hiu chung: cc knh ion c cng;

cc receptor enzyme; cc protein mng tbo hot ng thng qua cc protein G; ccprotein nhn lin kt vi cc steroid v hot ng nh cc yu t phin m; ccprotein mng thu ht v hot ha cc protein kinase ha tan; v cc receptor bm dnhmang thng tin gia cht nn ngoi bo v bxng tbo.

12.2 CC KNH ION C CNG

Tn hiu in nm di cc knh ion trong cc tbo trng thi bkch hot

Tnh nhy ca cc tbo cm gic v cc tbo thn kinh, cc tbo c phthuc vo cc knh ion, cc cht truyn tn hiu m nhng cht ny to ra mt conng iu ha s di chuyn ca cc ion v c nh Na+, K+, Ca+ v Cl- qua mng

plasma p ng vi cc kch thch khc nhau. Nhli tChng 11 cc knh ionny c "c cng"; chng c th m hoc ng, ty thuc vo s lin kt vireceptor c hot ha bi cc lin kt ca tn hiu chuyn bit ca n ( cho v dmt cht dn truyn thn kinh chng hn) hay l bi mt s thay i trong in thmng, Vm. Na+K+ATPase to ra mt smt cn bng in tch qua mng plasma bngcch mang 3 Na+ ra ngoi tbo cho 2 K+i vo (Hnh 12-3a.), lm cho bn trongmng tch in m hn so vi bn ngoi mng. Mng c gi l phn cc. Theo quy

c, Vmc gi trm khi bn trong tbo tch in m hn so vi bn ngoi. i vimt tbo ng vt in hnh, Vm= -60 n -70 mV.

Bi v cc knh ion thng cho cc ion m hoc cc ion dng i qua nhngkhng ng thi chai ion cng i qua, dng ion qua mt knh gy ra sphn bliin tch hai bn ca mng tbo lm thay i Vm. Dng ion mang in dng ivo nh Na+hay dng ion mang in m i ra nh Cl-, gy ra skhcc ca mng va Vmtin gn ti khng. Ngc li, dng K+i ra gy ra sphn cc ca mng vVmtrnn m hn. Nhng dng ion ny qua cc knh ion th thng, ngc li vi

svn chuyn tch cc ca Na+

K+

ATPase.


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Hnh 12-3.in th xuyn mng. (a)Na+K+ATPase tch in to ra mt in thxuynmng60 mV ( bn trong tch in m). (b)Cc mi tn mu xanh da tri cho thy hngm cc ion c khuynh hng di chuyn qua mng plasma trong mt tbo ng vt, bi skt hp ca cc gradient ha hc v in trng. Gradient ha hc ko Na+v Ca2+vo trong( gy ra skhcc) v y K+ra ngoi ( squ phn cc). Gradient in trng y Cl-rangoi, chng li gradient nng ca n ( gy ra skhcc).

Bng 12-2. Cc nng ion trong cc tbo v cc dch ngoi bo ( mM)

Hng dng chy ion tpht qua mt mng phn cc c quyt nh bi in

thha hc ca ion qua mng. Lc (G) lm cho mt ion dng ( Na+) ty i vobn trong thng qua mt knh ion l mt hm sca tlcc nng ca n hai

bn mng (Cin / Cout) v ca skhc bit vin th(hoc Vm):


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Trong :RIS l hng skh, T l nhit tuyt i, Z l in tch ca ion, v l

hng sFaraday. Trong mt tbo thn kinh hoc tbo myocyte in hnh, cc nng ca Na+, K+, Ca2+v Cl- trong cytosol th rt khc vi cc nng cc ion nytrong dch ngoi bo (Bng 12-2). Vi nhng khc bit ca cc nng ny, phn cnli ca Vmca -60 mV, v mi lin htrong phng trnh 12-1, smca knh Na+hoc Ca 2+ s dn n kt qumt dng Na+hoc Ca 2+bn trong (v skh cc),trong khi vic mmt knh K+sdn n kt qudng K+bn ngoi ( phn cc) (Hnh 12-3b).

Mt loi ion tip tc i qua mt knh khi v chkhi c skt hp ca khuynh nng v in th to nn mt lc dn, theo phng trnh 12-1. V d, nh Na+xung khuynh nng n khcc mng. Khi in thmng t n +70 mV, nhhng ca in th mng ny ( ngn Na+ i vo ) cn bng vi nh hng cakhuynh nng Na+( to ra nhiu Na+i vo trong). Ti in thcn bng ny(E), lc dn ( G) c xu hng di chuyn mt ion l 0. in thcn bng th khcnhau i vi tng loi ion v khuynh nng khc nhau i vi mi ion.

Slng cc ion phi i qua c ththay i ng kin thmng l tngi nhso vi nng ca Na+, K+ v Cl- trong tbo v dch ngoi bo, do ccdng chy ion xy ra trong struyn tn hiu trong cc tbo dbkch thch thccht khng nh hng n nng ca cc ion. Tuy nhin, bi v nng trong t

bo ca Ca2+ ni chung l rt thp (~10-7M), dng Ca2+i vo c thlm thay ing k[Ca2+] trong cytosol.

in thmng ca mt tbo ti mt thi gian nht nh l kt quca cc loiv s lng knh ion m trong thi im . Trong hu ht cc tbo trng thingh, cc knh K+th mnhiu hn cc knh Na+, Cl- hoc Ca2+v do in thnghgn vi E hay K+(- 98 mV) hn so vi bt kion no khc. Khi cc knh Na+,Ca2+ hoc Cl-m, in thmng tin gn n gi trE cho ion . Vic ng v mng thi gian ca cc knh ion v kt qul sthay i nht thi in thmng nmdi tn hiu in lm cho h thng thn kinh kch thch c xng co li, tim p,hoc cc t bo kch thch bi tit gii phng. Hn na, nhiu hormone gy ranhng nh hng bng cch thay i cc in thmng ca cc tbo mc tiu. Ccc chny khng gii hn i vi ng vt bc cao; cc knh ion ng vai tr quantrng trong cc phn ng ca vi khun, nguyn sinh vt, v thc vt vi cc tn hiumi trng.

minh ha hot ng ca cc knh ion trong struyn tn hiu tbo n tbo, chng ti m tcc c chm theo mt neuron truyn qua mt tn hiu dctheo chiu di ca n v qua mt synape n cc neuron tip theo (hoc n mt


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myocyte) trong mt chu ktbo, sdng acetylcholine nhl cht dn truyn thnkinh.

Nicotinic Acetylcholine receptor l mt knh ion kim sot nhligand

Mt trong nhng v ddhiu nht ca mt knh ion kim sot nhligandlnicotinic acetylcholinereceptor( xem hnh. 11-51). Knh receptor mkhi p ngvi acetylcholine dn truyn thn kinh (v n nicotine, do c tn nh vy ).Receptor ny c tm thy trong mng sau synap ca cc tbo thn kinh mt visynape v trong cc si c ( cc tbo c) ti cc nt thn kinh c.

Acetylcholine gii phng bi mt tbo thn kinh bkch thch khuch tn mtvi micromet qua khe synape hay nt thn kinh - c n tbo thn kinh sau synaphoc tbo c, ti n tng tc vi acetylcholine receptor v gy nn skch thchxung in (khcc) ca tbo nhn. Acetylcholine receptor l mt protein dlp th(allosteric) vi hai vng lin kt c i lc cao vi acetylcholin, khong 3,0 nm tcngion, trn hai tiu n v. Sgn ca acetylcholine gy ra mt sthay i thnh th

ng n m. Qu trnh c hp tc tch cc: lin kt ca acetylcholine vi vng utin lm tng i lc lin kt ca acetylcholine vi vng thhai. Khi tbo trc synapgii phng mt xung ngn ca acetylcholine, chai vng trn receptor tbo trcsynape bchong chv knh m(Hnh. 12-4). Na hay Ca2+c thi qua v cc dngion ny i vo gy ra skh cc ca mng plasma, khi u cho skin tip theothay i theo loi m. Trong mt tbo thn kinh sau synap, skhcc bt u mtin thhot ng (xem bn di); ti mt nt thn kinh c, skhcc ca cc si cgy co c.


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Hnh 12-4. Ba trng thi ca acetylcholine receptor.Sphi by ngn ca knh ion ngh( ng) (a)vi acetylcholine (Ach) gy ra trng thi bkch thch (b).Sphi by lu hndn n skhcc (c)v ng knh.

Thng thng, nng acetylcholine trong khe synape nhanh chng bhxungbi enzyme acetylcholinesterase, c mt trong khe. Khi cc nng acetylcholine duytr mc cao hn trong mt vi mili giy, receptor bmt tnh nhy cm ( Hnh 12-

1c). Knh receptor c chuyn n mt hnh ththba (Hnh. 12-4c), knh bng v acetylcholine lin kt rt cht. Vic gii phng chm (trong hng chc miligiy) acetylcholine t cc vng lin kt ca n cho php receptor tr li trng thinghv nhy vi cc nng acetylcholine.

Cc knh ion c cng in p sn xut cc in thhot ng thn kinh

Tn hiu trong hthng thn kinh c thc hin nhmt mng li ca cc tbo thn kinh, l cc tbo c bit ha thc hin mt xung in (in thhot ng) tmt u ca tbo ( c thtbo) thng qua mt phn mrng ca t

bo cht ko di ( si trc). Tn hiu in lm gii phng cc phn tdn truyn thnkinh synap, mang tn hiu n tbo tip theo trong mch. Ba loi knh ion c cngin p rt cn thit vi c chtruyn tn hiu ny. Dc theo ton bchiu di ca sitrc l cc knh Na+c cng in p (Hnh 12-5;. xem thm hnh 11-50), ng li khimng trng thi ngh(Vm= - 60 mV) nhng chmmt thi gian ngn khi mng bkhcc p ng vi acetylcholin (hoc mt scht dn truyn thn kinh khc). Skhcc xy ra l do cc knh Na+ mlm cho cc knh K+c cng in p m, vkt qu l K+ i ra gy ti phn cc mng. Mt xung ngn ca qu trnh khcc iqua trc thn kinh nh l skhcc bt u smcc knh ion Na+ sau cc knh K+.Sau khi mi mt knh Na+ mth knh khng thmli trong sut giai on na do sng in t mt chiu ca trng thi kh cc qut t thn t bo thn kinh


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vpha cui ca si trc. nhy in p ca cc knh ion l do shin din ti ccvtr quan trng knh protein ca cc chui bn amino acid tch in tng tc vivng in trng qua mng. Nhng thay i in p xuyn mng to ra nhng thayi tinh vi vhnh dng knh protein (xem hnh 11-50).

Ti u mt ca si trc l cc knh Ca2+c cng in p. Khi sng in ca skhcc chm n cc knh ny, chng mra, v Ca 2+i vo tkhng gian ngoi

bo. Sgia tng [Ca2+] trong tbo cht v gy ra sphng thch acetylcholine rangoi i vo khe synape (bc 3 trong hnh 12-5). Acetylcholine lan truyn ti cc t

bo sau synap ( t bo thn kinh hoc mt t bo c), n lin kt vi ccacetylcholine receptor v gy nn skhcc. Nh vy xung in c chuyn n t

bo tip theo trong mch.

Chng ti quan st thy, sau , cc knh ion c cng truyn t cc tn hiutheo mt trong hai cch: bng cch thay i nng trong cytosol ca mt ion (nhCa2+), sau p ng nh l mt cht truyn tn hiu thhai trong tbo ( hormonehay cht dn truyn thn kinh l cht truyn tn hiu u tin), hoc bng cch thayi Vmv nh hng n cc protein mng khc nhy vi Vm. Vic truyn qua mt tnhiu in qua mt tbo thn kinh v n cc tbo thn kinh tip theo minh ha chai c ch.

Hnh 12-5.Vai tr ca cc knh ion c cng in p vcng ligand trong struyn xung thn kinh.u tin,mng plasma ca tbo thn kinh trc synape phn cc

( bn trong tch in m) thng qua hot ng ca Na+K+ATPase mang in, bm 3 Na+ ra ngoi v 2 K+ c

bm vo neuron ( xem hnh 12-3). Mt skch thchneuron ny gy ra mt in thhot ng di chuyn dctheo si trc ( mi tn mu trng) cch xa thn tbo.Knh Na+ c cng in p mcho php Na+i vo, vkt qu l skh cc cc b lm cho knh Na+gn km v tip tc. S nh hng di chuyn ca in thhot ng c m bo bi giai on chu nhit ngntheo sau s m knh Na+ c cng in o. Khi lm

sng kh cc chm ti u si trc, cc knh Ca2+

ccng in p m, cho php Ca2+ i vo neuron trcsynape. Kt qu tng [Ca2+] bn trong kch thch sgii phng exocytic ca cht dn truyn thn kinhacetylcholine vo khe synape. Acetylcholine lin ktvi mt receptor trn neuron sau synape, lm m knhion c cng ligand. Na+v Ca2+ngoi bo i vo quaknh ny, khcc tbo say synape. Tn hiu in do i qua thn t bo ca neuron sau synape v s dichuyn dc theo si trc n mt neuron thba bi trnh

ttng ng ca cc trng hp ny.


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Cc tbo thn kinh ( neuron) c cc knh ththp ng vi cc cht truynxung thn kinh

Cc tbo ng vt, c bit l nhng tbo ca hthng thn kinh, cha nhiuknh ion c cng c kim sot bi cc tn hiu, in p, hoc chai. Cc cht dntruyn thn kinh 5-hydroxytryptamine (serotonin), glutamate, v glycine tt cc thhot ng thng qua cc knh receptor lin quan n acetylcholine receptor. Serotoninv glutamate hot ha smcc knh ion dng (K+, Na+, Ca2+) trong khi glycinehot ha s m cc knh chuyn bit Cl-. Cc knh ion dng v ion m ch khcnhau rt nh trong cc gc amino acid sp hng qua knh a nc. Cc knh iondng c cc chui bn Glu v Asp tch in m ti cc vtr quan trng. Khi mt vigc trong snhng gc c tnh acid c thay thbng cc gc c tnh kim, knhion dng (cation) c chuyn thnh knh ion m (anion).

Ty thuc vo ion i qua mt knh, tn hiu ( cht dn truyn thn kinh ) ng viknh c th kh cc hay siu phn cc tbo ch. Mt t bo thn kinh ring lthng thng nhn tn hiu u vo tmt vi (hoc nhiu) tbo thn kinh khc,tng tbo thn kinh gii phng cht dn truyn thn kinh c trng vi nh hngkhcc hay qu phn cc c trng. Do Vmca cc tbo ch tng ng vi uvo tch hp (Hnh 12-1d) tnhiu tbo thn kinh. Tbo p ng vi mt in thhot ng chkhi u vo tch hp thm n mt skhcc c ln va .

Cc knh receptor vi acetylcholine, glycine, glutamate, v gamma -aminobutyric acid (GABA) c cng bi cc tn hiu ngoi bo. Cc cht truyn tnhiu thhai ni bo nh l cAMP, cGMP (3', 5' - cyclic GMP, mt cht tng tgnging vi cAMP), IP3 (inositol 1,4,5-trisphosphate), Ca2+, v ATP- iu ha cc knhion ca lp khc nh chng ta sthy trong phn 12.7, tham gia vo s truyn cmgic ca thgic, khu gic v vgic.


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TM TT 12.2

Cc knh ion kim sot cng nhligand hoc in thmng l trung tm truyntn hiu trong cc tbo thn kinh v cc tbo khc.

Acetylcholine receptor ca cc tbo thn kinh v cc tbo c l mt knh ionkim sot cng nhligand.

Cc knh Na+ v K+ kim sot cng nhin th ca cc mng tbo thn kinhtruyn in p hot ng dc theo si trc nh mt sng khcc ( dng Na+i vo)tip theo l ti phn cc (K+i ra).

Sxut hin ca mt in thhot ng lm gii phng cht dn truyn thn kinhttbo trc synape. Cht truyn thn kinh (acetylcholin, cho v d) lan truyn ti

cc tbo sau synap, lin kt vi cc receptor chuyn bit trong mng plasma, v lmthay i Vm.

12.3 CC RECEPTOR ENZYME

Mt cchkhc ca struyn tn hiu c thc hin bi cc receptor enzyme.Nhng protein ny c mt domain lin kt tn hiu trn bmt ngoi bo ca mngplasma v mt vng hot ng enzyme mt pha ca tbo cht (cytosol), vi haidomain ni vi nhau bng mt on xuyn mng n l. Thng thng, cc receptorenzyme l mt protein kinase phosphoryl ha cc gc Tyr trong cc protein ch c

hiu; insulin receptor l receptor u tin cho nhm ny. thc vt, protein kinaseca receptor c hiu vi cc gc Ser hoc Thr. Cc receptor enzyme khc tng hpcGMP cht truyn tin thhai ni bo p ng vi cc tn hiu ngoi bo. Receptorvi yu tli niu thuc tm nh th in hnh ca loi ny.

Insulin receptor l mt protein kinase c hiu vi Tyrosine

Insulin iu ha cbiu hin gen v qu trnh bin dng: tn hiu insulin i treceptor mng plasma n cc enzym chuyn ha nhy vi insulin v vo nhn, nim n kch thch sphin m ca cc gen c hiu. Insulin receptor hot ng bao

gm hai chui ging nhau nh ra tmt ngoi ca mng plasma v hai tiu n vxuyn mng vi ui carboxyl hng vo cytosol (Hnh. 12-6, bc 1). Cc chui cha domain lin kt vi insulin, v cc domain ni bo ca cc chui cha hottnh protein kinase chuyn mt nhm phosphoryl tATP cho nhm hydroxyl ca ccgc Tyr trong cc protein ch c hiu. Tn hiu truyn qua insulin receptor bt u(bc 1) khi lin kt ca insulin vi cc chui hot ha hot tnh Tyr kinase ca ccchui , v mi gc phosphoryl ha ba gc Tyr quan trng gn ui carboxyl cachui trong dimer. Sphosphoryl ha tngny lm vng hot ha mra v th

enzyme c thphosphoryl ha cc gc Tyr ca ccprotein ch khc (Hnh. 12-7).


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Mt trong cc protein ch (Hnh. 12-6, bc 2) l ccht - insulin receptor 1(IRS-1). Mi ln phosphoryl ha cc gc Tyr ca n, IRS-1 trthnh tm im chomt phc hp cc protein (bc 3) mang cht truyn tin t insulin receptor n cc

protein ch trong cytosol v nhn, thng qua mt chui di cc protein trung gian.

u tin, mt gc -Tyr trong IRS-1 c lin kt bi domain SH2 ca proteinGrb2. (SH2 l ch vit tt ca Src homology 2; cc trnh t ca cc domain SH2tng tvi mt trnh tca cc domain trong protein Tyr kinase khc, Src ( ( phtm l sark)). Mt scc protein tn hiu cha cc min SH2, tt cu lin kt vicc n phn -Tyr trong mt protein tn hiu khc. Grb2 cng cha mt domainlin kt vi protein thhai, SH3, gn vi cc vng giu cc gc Pro. Grb2 gn vimt vng giu proline ca Sos, bsung Sos vi phc hp receptor ang hnh thnh.Khi lin kt vi Grb2, Sos xc tc s thay th lin kt GDP bi GTP trn Ras, mttrong cc protein lin kt vi nucleotide guanosine (cc protein G) qua trung gian mt

lot struyn tn hiu (Phn 12.4). Khi GTP c lin kt, Ras c thhot ha mtprotein kinase, Raf-1 (bc 4), protein kinase u tin trong ba protein kinase - Raf-1,MEK, v ERK - hnh thnh mt dng thc ( cascade) m mi kinase hot ha gc tiptheo bi sphosphoryl ha (Bc 5). Protein kinase EPK protein c hot ha bisphosphoryl ha ca cmt gc Thr v mt gc Tyr. Khi bhot ha, n gin tipgy ra mt snh hng sinh hc ca insulin bng cch i vo nhn v phosphorylha cc protein nh Elk1, iu chnh s phin m ca khong 100 gen iu hainsulin (bc 6).

Cc protein Raf-1, MEK, v ERK l cc thnh vin ca ba hln hn, m mts danh php c chn. ERK l mt thnh vin ca h MAPK ( cc proteinkinase hot ha phn bo; cc cht kch thch phn bo ( mitogen) l cc tn hiu hotng tbn ngoi tbo to ra qu trnh nguyn phn v phn chia tbo). Ngaysau khi pht hin MAPK u tin, enzyme c bit l s c hot ha bi

protein kinase khc, c gi l MAP kinase kinase ( MEK thuc vhny); v khimt kinase thba hot ha MAP kinase kinase c pht hin, c tn l MAP kinasekinase kinase (Raf-1 l mt thnh vin ca hny;. Hnh 12-6). Nhng chvit tt

n gin hn cho ba hny l MAPK, MAPKK, v MAPKKK. Cc kinase trong cchMAPK v MAPKKK chuyn bit vi cc gc Ser hoc Thr, nhng cc MAPKK(MEK) phosphoryl ha mt gc Ser v MAPK ( ERK) phosphoryl ha mt gc Tyrtrong ccht ca chng.

Cc nh ha sinh hc hin nay cng nhn con ng insulin nhl mt v dca mt chchung hn, trong cc tn hiu hormone, thng qua cc con ngtng tc thhin trong hnh 12-6, kt qul sphosphoryl ha cc enzym ch

bi cc protein kinase. Mc tiu ca sphosphoryl ha thng l protein kinase khc,sau phosphoryl ha mt protein kinase thba, v ctip tc nhvy. Kt qulmt thc phn ng khuch i tn hiu ban u bi nhiu mc cng (xem hnh.12 1b) Cc thc phn ng nh vy th hin trong hnh 12 6 c gi l thc MAPK


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Hnh 12-6. Siu ha biu hin gen bi insulin. Insulin receptor bao gm hai chui mt ngoi mng plasma v hai chui ngang qua mng v nh ra tbmt tbo cht. Linkt ca insulin vi cc chui to ra s thay i hnh th cho php s phosphoryl ha tng ca cc gc Tyr trong domain c ui carboxyl ca cc tiu n v. Sphosphorylha tng hot ha domain Tyr kinase, sau xc tc sphosphoryl ha ca cc proteinch khc. Con ng truyn tn hiu do insulin iu ha sbiu hin ca cc gen chuyn

bit bao gm mt thc cc protein kinase, mi thc hot ha thc ktip. Insulin receptor lmt Tyr-specific kinase; cc kinase khc ( tt cthhin mu xanh da tri) phosphoryl hacc gc Ser hay Thr. MEK l mt dual-specific kinase, phosphoryl ha cgc Thr v Tyrtrong ERK ( extracellular regulated kinase); MEK hot ha mitogen, EPK hot ha kinase;SRF l nhn tp ng huyt thanh. S tm tt cho cc thnh phn khc c gii thchtrong on vn.


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Hnh 12-7.Shot ha insulin-receptor Tyr kinase bng sphosphoryl ha tng. (a)dang bt hot ca domain Tyr kinase ( PDB ID 1IRK), shot ha loop ( xanh dng)nm trong vng hot ha, v khng c cc gc Tyr ti hn ( cc cu trc bng v gy c mu

en v ) c phosphoryl ha. Hnh thny bn bi lin kt hydrogen gia Tyr1162 vAsp1132. (b)Khi insulin lin kt vi cc chui ca cc insulin receptor, Tyr kinase ca mitiu n v ca dimer phosphoryl ha ba gc Tyr ( Tyr1158, Tyr1162, v Tyr1163) trn tiun v khc ( thhin y; PDB ID 1IR3). ( Cc nhm phosphoryl c m tnh l mtnguyn tphospho lp y khng gian mu cam v cc nguyn toxygen c cu trc bngv gy mu ). nh hng ca sgii thiu ba gc - Tyr thc y mt sthay i 30Aotrong vtr ca shot ha vng (loop), cch xa vng gn vi c cht, trnn c sn lin kt v phosphoryl ha mt protein ch, thhin y nh mt mi tn mu .

Grb2 khng phi l protein duy nht lin kt vi IRS-1 c phosphoryl ha.

Enzyme phosphoinositide 3 - kinase (PI-3K) gn IRS-1 qua domain SH2 mi hnhthnh (Hnh. 12-8). Do , PI-3K c hot ha chuyn phosphatidylinositol 4,5 -

bisphosphate mng lipid (Xem hnh. 10-15), cng c gi l PIP2, thnhphosphatidylinositol 3,4,5-trisphosphate (PIP3). Khi gn vi PIP3, protein kinase B(PKB) bphosphoryl ha v bhot ha bi mt protein kinase khc, PDK1. PKB c hot ha sau phosphoryl ha cc gc Ser hoc Thr trn cc protein ch, mttrong s l glycogen synthase kinase 3(GSK3). dng hot ha khng b

phosphoryl ha, GSK3 phosphoryl ha glycogen synthase, bt hot n v qua gpphn lm chm qu trnh tng hp glycogen. (Cchny c cho l chgii thchmt phn nhng nh hng ca insulin n s chuyn ha glycogen.) Khi bphosphoryl ha bi PKB GSK3 b bt hot Bi do vic cn s bt hot ca


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glycogensynthase trong gan v c, cc thc phn ng ca sphosphoryl ha proteinkhi u bi insulin kch thch s tng hp glycogen (Hnh. 12-8). Trong c, PKBkch hot sdi chuyn ca cc cht vn chuyn glucose (GLUT4) tcc ti ni bon mng plasma, kch thch glucose hp thu tmu (Hnh 12-8;. xem thm Bng 11-

2). PKB cng c chc nng mt scon ng truyn tn hiu khc, bao gm ckch hot bi -tetrahydrocannabinol (THC), thnh phn hot ng ca b (marijuana) v cn sa ( hashish).

Hnh 12.8 Hot ha glycogen bng insulin. Struyn tn hiu qua trung gian PI-3Kv PKB


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THC hot ha receptor CB1 trong mng sinh cht ca cc tbo thn kinh trongno, gy ra mt thc tn hiu c lin quan n MAPKs. Mt tm quan trng ca shot ha CB1 l skch thch cm gic thm n, mt trong cc nh hng r nht cavic s dng cn sa. Cc tn hiu thng thng i vi receptor CB1 l cc

endocannabinoid nh anandamide p ng bo v no t c tnh ca hot tnhthn kinh qu mn v dnhtrong mt cn co git ng kinh. Cn sa c trong nhiuthkqua c sdng trong iu trbnh ng kinh.

Nh trong tt ccc con ng truyn tn hiu, c mt c ch kt thc struyn tn hiu thng qua con ng PI 3K-PKB. Mt PIP3phosphatase c hiu(PTEN ngi) loi bphosphate v tr th3 ca PIP3to ra PIP2, khng cnp ng nhl mt vng lin kt vi PKB, v chui tn hiu bngt Trong nhiu loiung thtin trin, cc tbo khi u thng c mt khim khuyt trong gen PTEN vdo c cc mc cao bt thng ca hot tnh PIP3v PKB. Kt qudng nhl

mt tn hiu lin tc cho sphn chia tbo v stng trng ca khi u.

Ci g thc y stin ha ca bmy iu ha phc tp? Hthng ny chophp mt receptor b hot ha hot ha mt s phn t IRS-1, khuch i tn hiuinsulin, v shi tca cc tn hiu tmt sreceptor, mi receptor trong s cthphosphoryl ha IRS-1. Hn na, v IRS-1 c thhot ha bt kmt sprotein ccha cc domain SH2, mt receptor ring lhot ng thng qua IRS-1 c thkchhot hai hoc nhiu con ng truyn tn hiu; insulin nh hng n sbiu hin genthng qua con ng Grb2-Sos-Ras-MAPK v schuyn ha glycogen thng qua conng PI-3K-PKB.

Insulin receptor l receptor u tin cho mt s receptor enzyme vi mt cutrc tng ng v hot tnh receptor Tyr kinase. Cho v d, cc receptor vi yu ttng trng biu b v yu ttng trng c ngun gc ttiu cu c cc im tngng vcu trc v trnh tvi receptor insulin, v chai u c mt protein c hottnh Tyr kinase phosphoryl ha IRS-1. Nhiu receptor trong sny dimer ha sau khilin kt vi ligand; insulin receptor l mt dimer trc khi lin kt vi insulin. Linkt ca cc protein adaptor nhl Grb2 vi cc n phn -Tyr l mt cchchungthc y cc tng tc protein-protein, mt chm chng ti strli trong phn12.5.


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Ngoi cc receptor hot ng nh nhng protein Tyr kinase, mt s proteinmng ging receptor c protein c hot tnh Tyr phosphatase. Da trn cc cu trcca cc protein ny, chng ta c th phng on cc tn hiu ca chng l nhngthnh phn ca cht nn ngoi bo hoc cc bmt ca cc tbo khc. Mc d cc

vai tr truyn tn hiu ca chng cha c hiu r cng nhcc Tyr kinase receptor,chng r rng c khnng o ngc cc hot ng ca cc tn hiu kch thch cckinase ny.

Mt sbin i ca Tyr kinase receptor c quan st cc receptor khng chot tnh protein kinase bn thnhng khi bxm chim bi tn hiu ca chng, linkt vi mt Tyr kinase ha tan. Mt v dl hthng iu ha shnh thnh ca cctbo hng cu cc loi ng vt c v. Cytokine(tn hiu pht trin) cho hthngny erythropoietin (EPO), mt protein c 165 amino acid c sn xut thn. Khi

EPO lin kt vi receptor mng plasma (Hnh. 12-9), receptor dimer ha v c thlinkt ngay vi JAK protein kinase ha tan (Janus kinase). Lin kt ny hot ha JAK JAK phosphoryl ha mt sgc Tyr trong domain tbo cht ca EPO receptor. Mthca cc yu tphin m, gi chung l STATs ( cc cht truyn tn hiu v cc chthot ha sphin m), cng l cc mc tiu ca hot tnh kinase JAK. Mt domainSH2 STAT5 lin kt vi cc gc -Tyr trong EPO receptor, nh v n JAK

phosphoryl ha. Khi STAT5 c phosphoryl ha phn ng vi EPO, n to thnhcc dimer, biu hin mt tn hiu vn chuyn vo nhn. Trong nhn, STAT5 to ra s

biu hin ( phin m) cc gen c hiu cn thit cho strng thnh ca tbo hng

cu. H thng JAK-STAT ny hot ng mt scon ng truyn tn hiu khc,bao gm i vi hormone leptin, m tchi tit trong chng 23 (xem hnh. 23-34).JAK c hot ha cng c thkhi s, qua Grb2, thc MAPK (Hnh. 12-6), dn nthay i sbiu hin ca cc gen c hiu.


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Hnh 12-9.C chtruyn tn hiu JAK-STAT cho erythropoietin receptor.Lin kt caerythropoietin ( EPO) to ra sdimer ha ca EPO receptor, cho php Tyr kinase JAK hatan lin kt vi domain bn trong ca receptor v sphosporyl ha n trn mt sgc Tyr.

STAT protein STAT5 cha cha mt domain SH2 v lin kt vi cc gc -Tyr trnreceptor, mang receptor vo gn vi JAK. Sphosphoryl ha STAT5 bi JAK cho php haiphn t STAT dimer ha, mi phn t lin kt vi gc -Tyr khc. S dimer ha caSTAT5 phi by mt trnh tvng nhn ( NLS) m cc mc tiu STAT5 cho svn chuynvo nhn. Trong nhn, STAT gy ra sbiu hin ca cc gen c kim sot bi EPO. Mtcon ng truyn tn hiu thhai cng c bt u bi sphosphoryl ha tng ca JAKc kt hp vi EPO lin kt vi receptor ca n. Adaptor protein Grb2 lin kt -Tyrtrong JAK v bt u thc MAPK, nh l trong cc hthng insulin ( xem hnh 12-6).

Src l protein Tyr kinase ha tan khc lin kt vi cc receptor nht nh khi

chng lin kt vi cc ligand. Src l protein c tm thy u tin c domain gn -Tyr c trng sau c t tn l domain Src homology (SH2). V dkhc ca slin kt ca receptor vi mt protein kinase ha tan l h thng receptor ging Toll(TLR4) qua cc ng vt c v cc nh nghin cu pht hin mt c t mnh llipopolysaccharide (LPS) tvi khun. Chng ta quay trli hthng receptor gingToll trong mc 12.6, trong bi cnh ca stin ha ca cc protein truyn tn hiu.


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Receptor Guanylyl Cyclase to ra cht truyn tin thhai cGMP

Guanylyl cyclase ( Hnh. 12-10) l mt loi receptor enzym khc. Khi c hot

ha, mt guanylyl cyclase sn sinh ra guanosine 3, 5 - cyclic monophosphate (cyclicGMP, cGMP) tGTP:


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Hnh 12-10.Hai loi ( isozymes) guanylyl cyclase tham gia vo s truyn tn hiu. (a)

Mt isozyme tn ti trong hai dng bc qua mng tng ng c hot ha bi cc ligandngoi bo ca chng: atrial nutriuretic factor, ANF ( cc receptor trong cc tbo ca cc ngthn v c trn ca cc mch mu) v guanylin ( cc receptor trong cc tbo biu m rut).Guanylin receptor cng l mc tiu ca mt loi ni c tvi khun gy tiu chy cp tnh.(b)Isozyme khc l mt enzyme ha tan c hot ha bi nitric oxide ni bo ( NO); dangny c tm thy nhiu m, bao gm c trn ca tim v cc mch mu.


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GMP vng l mt cht truyn tin thhai mang cc thng tin khc nhau trong ccm khc nhau. Trong thn v rut n gy nn nhng thay i trong vn chuyn ion vginc; trong c tim (mt loi c trn) cc tn hiu ngh; trong no c th bao gmc trong spht trin v chc nng no ngi trng thnh. Guanylyl cyclase trongthn c hot ha bi cc hormone atrial natriuretic factor (ANF), c gii phng

bi cc tbo tm nh ca tim khi tim cng ra bi sgia tng thtch mu. bmmu n thn, ANF hot ha guanylyl cyclase trong cc tbo ca cc ng gp (hnh12-10a.). Kt qul [cGMP] tng thc y tng bi tit thn ca Na+v ca nc,dn n sthay i p sut thm thu. Smt nc lm gim thtch mu, chng likch thch m ban u dn n sbi tit ANF. C trn ca mch mu cng c mtANF receptor - guanylyl cyclase; lin kt vi receptor ny, ANF gy ra sgin (ginmch) ca mch mu, lm tng tc mu chy trong khi huyt p gim.

Mt guanylyl cyclase receptor tng ttrong mng plasma ca cc tbo biu

m rut c hot ha bi mt peptide rut, guanylyl, iu ha sbi tit Cl- trongrut. Receptor ny cng l mc tiu ca mt peptide ni c tbn vi nhit c titra bi Escherichia coli v vi khun gram m khc.[cGMP] cao do ni c tlm tngsbi tit Cl-v do lm gim s ti hp thu ca nc qua biu m rut gy tiuchy.

Mt loi guanylyl cyclase khc l mt cytosolic protein vi mt nhm heme linkt cht ch(Hnh 12-10b.), mt enzyme c hot ha bng nitric oxide (NO). Nitricoxide c sn xut targinine bi Ca2+phthuc NO synthase, c mt nhiu m

ng vt c v, v khuch tn ttbo ban u vo cc tbo ln cn. NO khng phn cc i qua cc mng plasma m khng c mt cht mang. Trong tbo ch,


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n lin kt vi nhm heme ca guanylyl cyclase v hot ho ssn xut cGMP. Trongtim, cGMP lm gim trng lc co bp bng cch kch thch cc bm ion phng thchCa2+tcytosol.

NO gy gin c tim c cng phn ng bi cc vin nitroglycerin v ccnitrovasodilator khc c dng gim bt cn au tht ngc, cn au do sco thtca tim khi thiu O2 do nghn ng mch vnh. Nitric oxide khng bn v hot ngtrong thi gian ngn; chhnh thnh trong vi giy, n tri qua qu trnh oxy ha thnhnitrite hoc nitrate. Cc Nitrovasodilator lm gin c tim trong thi gian di v chng

ph vhn vi gi, to ra mt trng thi bn ca NO. Gi trca nitroglycerin nh liu trau tht ngc c pht hin mt cch tnh c trong cc nh my sn xut

nitroglycerin nh mt cht ntrong nhng nm 1860. Cc cng nhn bau tht ngcbo co rng tnh trng ca h c ci thin nhiu trong sut tun lm vic, nhngcn au li trli vo nhng ngy cui tun. Cc bc s iu trcho nhng cng nhnny nghe cu chuyn ny qu thng xuyn n ni h to ra mi quan h, vmt loi thuc c tm ra.

Nhng nh hng ca s tng tng hp cGMP gim sau khi skch thch ktthc, bi v mt phosphodiesterase (cGMP PDE) c hiu chuyn cGMP thnh 5-GMP bt hot. Con ngi c mt sng dng ca cGMP PDE, vi sphn bm

khc nhau. ng dng trong cc mch mu ca dng vt b c ch bi thucsildenafil (Viagra) do cc nng cGMP vn cao mi khi c mt kch thch thchhp, cho thy cng dng ca loi thuc ny trong iu tr cc ri lon chc nngcng dng.

Hu ht cc hot ng ca cGMP ng vt c cho l qua trung gian biprotein kinase ph thuc cGMP, cng c gi l protein kinase G hoc PKG, khic hot ha bi cGMP, phosphoryl ha cc gc Ser v Thr trong cc protein ch.Cc domain xc tc v iu ha ca enzyme ny nm trong mt polypeptide n gin

(Mr ~80,000). Mt phn ca domain iu ha khp vi vng lin kt c cht. Lin kt


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ca cGMP thc y mt phn ca domain iu ha ra khi vng lin kt, hot hadomain xc tc.

GMP vng c mt m hnh hot ng th hai mt ng vt c xng (vertebrate eye): n to ra cc knh ion c hiu mtrong cc tbo nn v tbogy ca vng mc ( retinal rod). Chng ti quay tr li vai tr ny ca cGMP trongtho lun vsnhn trong phn 12.7.

TM TT 12.3

Insulin receptor l nguyn mu ( prototype) ca cc receptor enzym c hot tnh Tyrkinase. Khi insulin lin kt vi receptor ca n, mi gc ca receptor phosphoryl ha

chui cng loi, hot ha hot tnh Tyr kinase ca receptor. Kinase xc tc sphosphoryl ha cc gc Tyr trn cc protein khc nh IRS-1.

Cc gc -Tyr trong IRS-1 phn ng nh l cc vng lin kt vi cc protein vicc domain SH2. Mt vi protein trong sny , nh Grb2, c hai hoc nhiu hn ccdmain lin kt vi protein v c thp ng nh l cc adaptor mang hai protein lign nhau.

Cc tng tc protein-protein dn n GTP gn vo v hot ha Ras protein, do

kch hot mt thc protein kinase kt thc vi sphosphoryl ha cc protein chtrong cytosol v nhn. Kt qul nhng thay i chuyn ho chuyn bit v sbiuhin gen bbin i.

Mt s tn hiu, bao gm atrial natriuretic factor v peptide guanylyl rut, hotng thng qua cc receptor enzyme vi hot tnh guanylyl cyclase. cGMP c tora hot ng nh mt cht truyn tin th hai, hot ha cGMP ph thuc proteinkinase (PKG). Enzyme ny lm thay i qu trnh bin dng sphosphoryl ha ccenzyme c hiu.

Nitric oxide (NO) l mt cht truyn tin c thi gian tn ti ngn hot ng bngcch kch thch mt guanylyl cyclase tan, tng [cGMP] v kch thch PKG.


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12.4 CC RECEPTOR LIN KT VI PROTEIN G V CC CHTTRUYN TIN THHAI

Mt c chthba ca struyn tn hiu, phn bit cc knh ion c cng v ccreceptor enzyme, c xc nh bi ba thnh phn chnh: mt receptor mng plasma

vi by on xon xuyn mng, mt enzyme trong mng plasma to ra mt chttruyn tin thhai ni bo, v mt protein gn vi guanosine nucleotide (protein G). G

protein b kch thch bi receptor c hot ha, trao i lin kt GDP cho GTP;GTP-protein tch ra treceptor khng lin kt v lin kt vi mt enzyme gn , lmthay i hot tnh ca n. Gen ca ngi m ha nhiu hn 1.000 thnh vin ca hny ca cc receptor, chuyn bit cho cc cht truyn tin khc nhau nh nh sng, miv, v cc hormone. Receptor ca tuyn thng thn trung gian cc nh hng caepinephrine trn nhiu m, l nguyn mu (prototype) cho h thng truyn tn hiuny.

H thng th th adrenergic hot ng thng qua cht truyn tin th haicAMP

Hot ng Epinephrine bt u khi cc hormone lin kt vi mt proteinreceptor trong mng plasma ca mt tbo nhy vi hormone. Adrenergic receptors (tn "adrenergic" thay thcho epinephrine, adrenaline) l bn loi chung 1, 2, 1, 2c xc nh bi skhc bit rt nh trong i lc v phn ng ca chng vi mtnhm agonists v antagonists. Agonists l cc cht c cu trc tng ng lin kt vi

mt receptor v bt chc cc nh hng ca ligand tnhin ca n; antagonists lcc cht tng ng lin kt m khng gy ra cc nh hng thng thng v do ngn chn nhng nh hng ca agonists. Trong mt strng hp, i lc ca agonisttng hp hoc antagonists vi receptor ln hn so vi agonist tnhin (Hnh. 12-11).Bn loi adrenergic receptor c tm thy trong cc m ch khc nhau v qua trunggian cc phn ng khc nhau vi epinephrine. y chng ti tp trung vo cc -adrenergic receptor ca c , gan v m m. Nhng receptor ny qua trung gian thayi trong qu trnh chuyn ha nhin liu, nh m ttrong Chng 23,bao gm tngsphn hy ca glycogen v cht bo. Adrenergic receptors ca cc phn nhm 1v

2 hot ng thng qua c ch tng t, nh vy trong tho lun ny ca chng ti,"-adrenergic" p dng cho chai loi.


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Hnh 12-11.Epinephrine v cc ng phn tng hp ca n.Epinephrine cng c gil adrenaline, c gii phng ttuyn thng thn v iu ha chuyn ha sn xut nnglng trong c, gan v cc m m. N cng p ng nh l ch t dn truyn thn kinh trongadrenergic neurons. i lc ca n vi receptor ca n c biu hin nh l mt hng s

phn ly cho phc hp ligand-receptor. Isoproterenol v propanolol l cc ng phn tnghp, mt ng phn vi mt anagonic vi receptor cao hn i lc ca epinephrine vi

receptor,v mt antagonic khc c i lc rt cao vi receptor.

Adrenergic receptor l mt protein khng ththiu vi by vng knc ca 20n 28 gc amino acid " un khc" trli v qua mng plasma by ln. Protein ny lmt thnh vin ca mt hrt ln ca cc receptor, tt cvi by xon xuyn mngthng c gi l cc ththc cu trc un khc, cc receptor lin kt vi proteinG (GPCR), hoc 7 receptor phn on xuyn mng (7tm). .Lin kt ca epinephrinevi mt vng trn receptor nm su trong mng (Hnh. 12-12, bc 1) thc y mts thay i hnh th trong domain ni bo ca receptor nh hng n s tng tc

ca n vi protein thhai trong con ng truyn tn hiu, mt protein G kch thchlin kt vi GTP dtam phn (heterotrimeric), hoc GSpha bn cytosol ca mng

plasma.


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Alfred G. Gilman v Martin Rodbell pht hin ra rng khi GTP lin kt vi Gs,

Gs kch thch sn xut cAMP bi adenylyl cyclase (xem bn di ) trong mngplasma. Chc nng ca Gsnh l mt cng tc phn ttng ng ca mt lp ccprotein G c c trng bi Ras, tho lun trong mc 12.3 trong bi cnh cainsulin receptor. Vmt cu trc, Gsv Ras l kh khc bit; cc protein G ca loiRas l cc n phn (Mr~20,000), trong khi cc protein G c tng tc vi ccreceptor un khc l cc trimer ca ba tiu n vkhc nhau, (Mr 43.000), (Mr37.000), v (Mr 7.500 n 10.000) .

Hnh 12-12.Struyn tn hiu epinephrine: con ng -adrenergic. By bc ca cch lin kt bt cp ca epinephrine (E) vi receptor (Rec) ca n vi s hot ha caadenylyl cylcase (AC) c tho lun thm trong on vn. Phn tadenylyl cyclase tng

t trong mng plasma c thc iu ha bi mt protein G trng thi kch hot (Gs)c thhin hay mt protein G c ch( Gi, khng c thhin). Gsv Gichu nh hng


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ca cc hormone khc nhau. Cc hormone cm ng GTP lin kt vi Gi gy ra sc chadenylyl cyclase, kt qul [cAMP] trong tbo thp.

Khi vng lin kt vi nucleotide ca Gs(trn tiu n v) bchim bi GTP, Gshot ng v c thhot ha adenylyl cyclase (AC trong hnh 12-12.); vi GDP linkt vi vng, Gskhng hot ng. Lin kt ca epinephrine cho php receptor xc tcchuyn lin kt GDP bng GTP, chuyn Gsthnh dng hot ng ca n (bc 2).Khi iu ny xy ra, cc tiu n v v ca Gsphn tch ttiu n v, v Gs,vi lin kt GTP ca n, di chuyn trong mt phng ca mng tbo tcc receptorn mt phn tgn adenylyl cyclase (bc 3). Gsc tp trung trn mng bimt nhm palmitoyl gn ng ha tr. (xem hnh. 11-14).

Adenylyl cyclase ( hnh 12 13) l mt protein ni ti ca mng plasma, vivng hot ha ca n trn bmt cytosol. N xc tc stng hp ca cAMP tATP:


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Lin kt ca Gshot ha vi adenylyl cyclase hot ha cyclase xc tc stng hp cAMP ( hnh 12 -12, bc 4), lm tng [cAMP] trong t bo cht (cytosolic). Skch thch ny bi Gsth bgii hn, Gsl mt GTPase chuyn GTPlin kt thnh GDP ( hnh 1214). Gsbbt hot khng lin kt tadenylyl cyclase,

tr li cyclase cha bhot ha. Sau khi Gsti kt hp vi cc tiu n v v (Gs), Gsxut hin li tng tc vi mt receptor lin kt vi hormone.

Hnh 12-13.Stng tc ca Gsviadenylyl cyclase ( PDB ID 1AZS).Nhn xctc tan ca adenylyl cyclase ( AC, xanhdng), tch ra tmng cnh ca n,c kt tinh vi Gs( xanh lc) nhn cutrc tinh thny. Terpene forskolin tthcvt ( mu vng) l mt loi thuc kch thchmnh enzyme v GTP ( mu ) lin kt viGskhi u stng tc ca Gsviadenylyl cyclase.

Hnh 12-14.S t bt hot ca Gs. Ccbc c m tthm trong on vn. Hottnh GTPase sn c ca protein, trong nhiutrng hp bkch thch bi cc protein RGS( cc cht iu ha s truyn tn hiu ca

protein G), quyt dnh cch GTP lin kt bthy phn thnh GDP nh thno v do G

protein duy tr hot tnh trong bao lu.

Mt nh hng xui dng ca epinephrine l hot ha glycogen phosphorylaseb. So ngc ny c thc y bi enzyme phosphorylase b kinase, xc tc sphosphoryl ha ca 2 gc Ser chuyn bit trong phosphorylase b, chuyn n thnhphosphorylase a ( xem hnh 6 -31). AMP vng khng nh hng trc tip nphosphorylase b kinase. ng hn l, protein kinase ph thuc cAMP c gi lprotein kinase A hay PKA, c hot ha bi cAMP ( Hnh 12 -12, bc 5), xc tcsphosphoryl ha ca phosphorylase b kinase bt hot to dng hot ng.


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Hnh 12-15. Shot ha ca protein kinase phthuc cAMP, PKA.(a)Mt sm tvtetramer R2C2bt hot, domain c chtng ca mt tiu n viu ha (R) chim chvng lin kt vi ccht, c chhot tnh ca tiu n vxc tc ( C). AMP vng hot haPKA bng cch phn tch cc tiu n vC tcc tiu n vc chR. PKA c hot hac thphosphoryl ha mt lot cc c cht protein ( bng 12-3) cha trnh tPKA ( X-Arg-(Arg/Lys)-X-(Ser/Thr)-B), X l gc bt k v B l gc k nc bt k), bao gm

phosphorylase b kinase. (b)Vng gn vi c cht ca mt tiu n vxc tc biu thbitinh thhc tia X ( xut pht tPDB ID 1JBP). Cc chui bn enzyme c bit th ti hntrong sgn vi c cht v tnh c hiu thhin mu xanh dng. C cht peptide ( mu) nm trong mt khe trn bmt enzyme, vi gc Ser ca n ( mu vng) nm trong vngxc tc. Trong tetramer R2C2bt hot, domain c chtng ca R nm trong khe ny, khalin kit vi c cht.

Dng bt hot ca PKA cha hai tiu n vxc tc ( C) v hai tiu n viuha ( R) ( hnh 12 15a), tng ng vtrnh tvi cc domain xc tc v iu ha caPKG ( protein kinase phthuc cGMP). Phc hp R2C2tphn (tetrameric) th hotng, bi v mt domain c chtng ca mi tiu n vR chim vng lin ktvi c cht ca mi tiu n vC. Khi cAMP lin kt vi hai vng trn mi tiu nvR, cc tiu n vR tri qua mt sthay i hnh thv phc hp R2C2kt hp

to ra hai tiu n vC hot ng tdo. C chc bn tng ng ny s dchchuyn ca mt domain c ch t ng qua trung gian s hot ha d lp th ca


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nhiu loi protein kinase bi cht truyn tin thhai ca chng. ( cho v dnh tronghnh 127 v 1223).

Trong hnh 12-12 ( bc 6), PKA iu ha mt senzyme ( bng 12 -3). Mc dcc protein c iu ha bi sphosphoryl ha phthuc cAMP c cc chc nnga dng, chng gn vo mt vng ca trnh t tng ng xung quanh gc Ser hayThr tri qua qu trnh phospohryl ha, mt trnh tnh du chng cho siu ha

bi PKA. Vng xc tc ca PKA ( Hnh 12 15b) tng tc vi mt vi gc gn Thrhay Ser trong protein ch, v nhng tng tc ny xc nh tnh c hiu ca c cht.Sso snh trnh tca mt scc c cht protein vi PKA to ra trnh t tngng cc gc ln cn chuyn bit cn nh du mt gc Ser hay Thr cho s

phosphoryl ha. ( xem bng 123).

Hnh 12-6. Siu ha biu hin gen bi insulin. Insulin receptor bao gm hai chui mt ngoi mng plasma v hai chui ngang qua mng v nh ra tbmt tbo cht. Linkt ca insulin vi cc chui to ra s thay i hnh th cho php s phosphoryl ha tng ca cc gc Tyr trong domain c ui carboxyl ca cc tiu n v. Sphosphorylha tng hot ha domain Tyr kinase, sau xc tc sphosphoryl ha ca cc proteinch khc. Con ng truyn tn hiu do insulin iu ha sbiu hin ca cc gen chuyn


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bit bao gm mt thc cc protein kinase, mi thc hot ha thc ktip. Insulin receptor lmt Tyr-specific kinase; cc kinase khc ( tt cthhin mu xanh da tri) phosphoryl hacc gc Ser hay Thr. MEK l mt dual-specific kinase, phosphoryl ha cgc Thr v Tyrtrong ERK ( extracellular regulated kinase); MEK hot ha mitogen, EPK hot ha kinase;

SRF l nhn tp ng huyt thanh. S tm tt cho cc thnh phn khc c gii thchtrong on vn.

Struyn tn hiu bi adenylyl cyclase ktha mt vi bc khuch i tn hiuhormone ban u ( hnh 12 16). u tin, lin kt ca phn t hormone vi mtreceptor hot ha mt vi phn t Gs. K n, bng vic hot ha mt phn tadenylyl cyclase, mi phn t Gshot ng kch thch s tng hp nhiu phn tcAMP. Cht truyn tin th hai cAMP hot ha PKA, mi phn t xc tc s

phosphoryl ha ca nhiu phn tca protein mc tiuphosphorylase b kinase tronghnh 12 -16. Kinase ny hot ha glycogen phosphorylase b, dn n s huy ngnhanh ca glucose tglycogen. Mang li nh hng ca thc l skhuch i catn hiu hormone bi mt vi mc cng , c tnh nng epinephrine ( hoc btkhormone no khc) cn n hot tnh hormone rt thp.

AMP vng, cht truyn tin thhai ni bo trong hthng ny, thi gian tn tingn. N b phn hy rt nhanh bi cyclic nucleotide phosphodiesterase thnh 5 AMP ( Hnh 1212, bc 7), khng hot ng nh mt cht truyn tin thhai:

Hnh 12-16. Thc epinephrine.Epinephrine kch hot mt chui ccphn ng trong cc tbo gan, m cc cht xc tc hot ha cc cht xctc, kt qu l skhuch i ln ca tnhiu. Lin kt ca mt slng nhcc

phn tca epinephrine vi cc receptor-adrnergic chuyn bit trn b mt t

bo hot ha adenylyl cyclase. minhha skhuch i, chng ti thhin 20phn tcAMP hot ha 10 phn tPKA,mi phn t PKA hot ha 10 phn tca enzyme ktip ( tng sl 100), vtip tc n cht th t. Nhng skhuch i ny c thkhng cho tngth.


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Tn hiu ni bo do vn cn tn ti khi v chkhi hormone receptor vn cnbchim chbi epinephrine. Cc methyl xanthine nh l caffeine v theophylline (mt thnh phn ca tr) c chphosphodiesterase, lm tng thi gian bn r cacAMP v do cc tc nhn c kh nng hot ng bi vic kch thch adenylyl

cyclase.

Thu th adrenergic bkhtnh nhy bi sphosphoryl ha

Cc hthng truyn tn hiu tri qua skhtnh nhy khi tn hiu vn tip tc.Skh tnh nhy ca adrenergic receptor qua trung gian bi mt protein kinase

phosphoryl ha receptor trong domain ni bo thng tng tc vi Gs( Hnh 12 -17).Khi receptor b chim bi epinephrine, adrenergic receptor kinase ( ARK)

phosphoryl ha cc gc Ser gn ui carboxyl ca receptor. Thng thng trongcytosol, ARK c ko n mng plasma bng slin kt ca n vi cc tiu n vGsv n c t vo phosphoryl ha receptor. Sphosphoryl ha to mt vnglin kt vi protein arrestin ( arr), cng c gi l arrestin 2, v lin kt ca arrestin cn s tng tc gia receptor v protein G. Lin kt ca arrestin cnglm cho stch ring receptor ra ddng, loi bcc receptor tmng plasma bi snhp bo thnh cc ti ni bo. Cc receptor trong cc ti ni bo bkhphosphorylha sau trli mng plasma, hon thnh chu trnh v khtnh nhy hthng viepinephrine. Adrenergic receptor kinase l mt thnh vin ca h G protein coupled receptor kinase ( GRKs), phosphoryl ha cc receptor c cu trc un khc

trn cc domain ca tbo cht ( cytosol) ui carboxyl ca chng v ng vai trtng tvi ARK trong skhtnh nhy v ti to tnh nhy ca cc receptor. Tithiu 5 GRKs khc nhau v 4 arrestin khc nhau c m ha trong gen ngi; miGRK c thkh tnh nhy mt tp hp cc receptor un khc, v mi arestin c thtng tc vi nhiu loi receptor c phosphoryl ha khc nhau.


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Bng 12-3. Mt senzyme v cc protein khc c iu ha bi sphosphorylha ph thuc cAMP ( bi PKA). * Gc S hay T c phosphoryl ha c biu dinmu . Tt cgc c vit nh l nhng chvit tt mt k t( xem bng 3-1). +X lamino acid bt k, B l amino acid knc bt k.

Trong khi cn tn hiu tmt receptor un khc tslin kt vi protein G, ccarestin cng c thbt u mt thc tn hiu thhai bng cch hot ng nhl cc

protein nng mang mt sprotein kinase hot ng trong mt thc. Cho v d, arestin lin kt vi receptor un khc cho angiotensin, mt cht iu ha huyt p,lin kt vi 3 protein kinase Ras 1, MEK1, v ERK ( Hnh 12 -18), p ng nh lmtprotein nng to iu kin cho bt kqu trnh truyn tn hiu, nh l tn hiuinsulin ( Hnh 12 -16) cn n ba protein kinase tng tc.iu ny l mt trongnhiu v dc bit ca s truyn tn hiu cho gia cc h thng c kch thch

bi cc ligand khc nhau ( trong trng hp ny l angiotensin v insulin).

Hnh 12-17. S kh tnh nhy ca receptor -adrenergic trong s hin din tip tcca epinephrine.Qu trnh ny qua trung gian bi hai protein: -adrenergic protein kinase (ARK) v -arestin (arr; arrestin 2).


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Hnh 12-18.-arrestin khng bt cp vi receptor un khc tprotein G ca n v mang baenzyme ca thc MAPK li gn nhau. nh hng l mt tc nhn kch thch khi u hai conng p ng ring bit: con ng c hot ha bi protein G v thc MAPK.

AMP vng hot ng nh l cht truyn tin thhai cho mt sphn tiu haEpinephrine ch l mt trong nhiu hormone, cc nhn t tng trng v cc

phn tiu ha khc hot ng bng cch thay i [cAMP] ni bo v do hottnh ca PKA ( bng 12 4). Cho v d, glucagon lin kt vi cc receptor ca ntrong mng plasma ca cc t bo m, hot ha ( vi mt protein Gs) adenylylcyclase. PKA, bi kch thch bi s tng [cAMP], phosphoryl ha v hot ha hai

protein chuyn cht bo dtrthnh cc acid bo ( perilipin triacylglycerol lipasenhy vi hormone; xem hnh 173), dn n shuy ng ca cc acid bo. Tng

t, peptide hormone ACTH ( adrenocorticotropic hormone, cng c gi lcorticotropin), c to ra bi thy trc tuyn yn, lin kt vi cc receptor chuynbit trong v tuyn thng thn, hot ha adenylyl cyclase v lm tng [cAMP] nibo. PKA sau phosphoryl ha v hot ha mt vi enzyme cn cho s tng hpcortisol v cc hormone steroid khc. Tiu n v xc tc ca PKA cng c th dichuyn vo nhn, n phosphoryl ha mt protein lm bin i sbiu hin cacc gen chuyn bit.

Mt vi hormone hot ng bng cch c ch adenylyl cyclase, lm gim cc

nng cAMP, v kh s phosphoryl ha protein. Cho v d, lin kt casomatostatin vi receptor ca n dn n shot ha ca mt protein G c ch, hayGi, tng ng vmt cu trc vi Gs, c chadenylyl cyclase v lm gim [cAMP].Somatostatin do i lp vi cc nh hng ca glucagon. Trong m m,

prostagladin E1 ( PGE1; xem hnh 1018b) c chadenylyl cyclase, do lm gim[cAMP] v lm gim s huy ng s d tr lipid b kch thch bi epinephrine vglucagon. Trong cc m khc PGE1 kch thch stng hp cAMP, bi v cc receptorca n bt cp vi adenylyl cyclase qua mt protein G kch thch, Gs. Trong cc mvi cc receptor 2adrenergic, epinephrine lm gim [cAMP], bi v cc thth2

bt cp vi adenylyl cyclase qua mt protein G c ch, Gi. Mt tn hiu ngoi bo nhl epinephrine hay PGE1 c thc nhng nh hng khc hon ton da trn cc m


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khc nhau ca cc loi tbo, phthuc vo ba nhn t: loi receptor trong mi m,loi protein G ( Gshay Gi) vi receptor c bt cp v nhm cc enzyme mc tiuPKA trong cc tbo.

Bng 12-4. Mt stn hiu sdng cAMP nh l cht truyn tin thhai.* Ccphn loi receptor trong nhng ngoc n hnh vung. Cc phn loi c thc cc c chtruyn tn hiu khc nhau. Cho v d, serotonin c pht hin mt sm nhcc phn loireceptor 5-HT-1a v 5-HT-1b, hot ng thng qua adenylyl cyclase v cAMP, v cc mkhc nhphn loi receptor 5-HT-1c, hot ng thng qua c chphospholipase C-IP3 ( xem

bng 12-5).

Mt nhn ttht gii thch cho cu hi nhiu tn hiu c thqua trung gian bimt cht truyn tin thhai n l( cAMP) l mt skhi u ca qu trnh truyn tn

hiu n mt vng chuyn bit ca tbo bi cc protein nng . AKAPs ( A kinaseanchoring protein) c ha tr hai; mt phn lin kt vi tiu n vR ca PKA, v


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phn khc lin kt vi mt cu trc chuyn bit trong tbo, hn chPKA n gncu trc . Cho v d, AKAPs chuyn bit lin kt PKA vi vi ng, cc si actin, ccknh Ca2+, ti thv nhn. Cc loi khc ca cc tbo c cc AKAP khc nhau v vycAMP c thkch hot sphosphoryl ha ca cc protein ti thtrong mt tbo v s

phosphoryl ha ca cc si actin trong tbo khc. Trong cc nghin cu vsinhvca cc bin i sinh ha, sinh ha gp sinh hc tbo, v cng ngh thng quaranh gii trnn v gi. ( Khung 122).

Hai cht truyn tin thhai xut pht tPhosphatidylinositols

Mt lp cc receptor un khc thhai c bt cp qua mt protein G vi mtphospholipase C ca mng plasma ( PLC) chuyn bit vi lipid phosphatidylinositol4,5bisphosphate mng plasma ( xem hnh 10 -15). Enzyme nhy vi hormone nyxc tc s hnh thnh hai cht truyn tin th hai: diacylglycerol v inositol 1.4.5 triphosphate, hay IP3( trnh nhm vi PIP3, trang 431).

Khi mt hormone ca nhm ny ( bng 12- 5) lin kt vi receptor chuyn bitca n trong mng plasma ( hnh 12 19; bc 1), phc hp receptor hormone xctc strao i GTP-GDP trn mt protein G lin kt, Gq( bc 2), hot ha n chnhxc nh l addrenergic receptor hot ha Gs ( xem hnh 12 -12). Gqbhot hachuyn qua hot ha mt PLC lin kt chuyn bit vi mng ( bc 3), xc tc ssn

xut hai cht truyn tin th hai diacylglycerol v IP3 bi s thy phnphosphatidylinositol 4.5bisphosphate trong mng plasma ( bc 4).

Inositol triphosphate, mt hp cht ha tan trong nc, khuch tn t mngplasma vo li ni cht, n lin kt vi cc IP3 receptor chuyn bit v to racc knh Ca2+trong ER m. Ca2+btch ra c phng thch vo cytosol (bc 5),v [Ca2+] trong cytosol tng mnh khong 10 -6M. Mt nh hng ca [Ca2+] cao lshot ha ca protein kinase C (PKC) .Diacylglycerol hp tc vi Ca2+trong shotha PKC, do cng hot ng nh l mt cht truyn tin th hai (bc 6). PKC

phosphoryl ha cc gc Ser hoc Thr ca cc protein mc tiu chuyn bit lm thayi cc hot tnh xc tc ca chng (bc 7). C mt s isozyme ca PKC, mi


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isozyme vi mt sphn btrong m c trng , c vai tr quyt nh tnh c hiuprotein ch.

Hot ng ca mt nhm cc hp cht c bit nh l cc cht hot ha khiu l do nh hng ca chng trn PKC. Cch hiu tt nht vcc hp cht ny l xemchng nh cc phorboleste, cc hp cht tng hp l cc cht hot ho mnh PKC.Chng dng nh bt chc diacylglycerol tbo nh l cc cht truyn tn thhai,nhng khng ging vi cc diacylglycerol t nhin chng khng c chuyn hanhanh chng. Bng cch kch hot lin tc PKC, nhng cht hot ha khi u ctng hp ny can thip vo siu ha bnh thng ca stng trng v phn chia

tbo (c tho lun trong mc 12.10).

Calcium l cht truyn tin thhai trong nhiu con ng truyn tn hiu

Trong nhiu tbo phn ng vi cc tn hiu ngoi bo, Ca2+p ng nh l mtcht truyn tin thhai to nn nhng phn ng trong tbo, chng hn nhsxut

bo trong cc tbo thn kinh v cc tbo ni tit, sco c, v s ti sp xp bxng tbo trong sut qua trnh di chuyn ca amip. Thng thng, [Ca2+ ] trong

cytosol mc rt thp (< 10- 7M) bi hot ng ca cc bm Ca2+trong ER, ty th,v mng plasma. Ni tit, thn kinh, hay tc nhn kch thch khc hoc to ra mtdng Ca2+i vo tbo thng qua cc knh Ca2+chuyn bit trong mng plasma haygii phng ca Ca2+ring bit tER hoc ty th, trong chai trng hp tng [Ca2+]trong cytosol v to ra mt phn ng ca tbo.


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Hnh 12-19.Hormone-activated phospolipase C and IP3. Hai cht truyn tin thhai nibo c sn xut trong hthng phosphatidylinositol nhy vi hormone: inositol 1,4,5-triphosphate (IP3) v diacylglycerol. Chai tham gia vo shot ha protein kinase C. Bng

cch tng [Ca2+

] trong cytosol, IP3cng hot ha cc enzyme khc phthuc Ca2+,

do Ca2+cng hot ng nh l cht truyn tin thhai.


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Bng 12-5. Mt stn hiu hot ng thng qua phospholipase C v IP3. * Ccphn loi receptor trong cc ngoc hnh vung, xem ch thch cui bng 12-4.

Thng thng, [Ca2+ ] khng chn gin l tng v sau gim dn, nhngthay v dao ng trong mt vi giy ( hnh. 12-20), thm ch ngay c khi nng hormone ngoi bo vn khng i. C chdi cc dao ng [Ca2+] c lp ngvi siu ha ngc bi Ca2+ca phospholipase to ra IP3 hoc knh ion iu haCa2+gii phng tER, hoc chai. D bt kc chno, th nh hng l mt loitn hiu ( cho v dl nng hormone) c chuyn thnh mt nhn tkhc( tn sv bin ca " spikes" [ Ca2+] ni bo).

Nhng thay i trong [Ca2+] ni bo c pht hin bi cc protein lin kt viCa2+iu ha mt lot cc enzyme phthuc Ca2+. Calmodulin ( CaM) ( Mr 17,000)l mt protein a acid vi bn vng lin kt vi Ca2+c i lc cao. Khi [Ca2+] ni botng n khong 10-6 ( 1 M), lin kt ca Ca2+vi calmodulin lm thay i hnh thprotein ( hnh 12 21). Calmodulin lin kt vi mt lot cc protein v trong linkt bn vi Ca2+iu ha cc hot tnh ca chng. Calmodulin l mt thnh vin camt hcc protein lin kt vi Ca2+cng bao gm troponin ( trang 185), kch thch sco c xng p ng vi [ Ca2+] tng. Hny ng gp mt cu trc lin kt vi Ca2+c trng l cu trc bn tay EF ( EF hand) ( Hnh 12 21c).

Hnh 12-20. To ra nhng dao ng trong [Ca2+] ni bo bng cc tn hiu ngoibo.(a)Mt thuc nhum ( fura) tri qua nhng thay i hunh quang khi n lin kt viCa2+ cho php khuch tn vo cc tbo v nng sut nh sng pht ra tc thi ca n co bi knh hin vi hunh quang. Cng hunh quang c biu thbng mu; thang mulin hcng mu vi [Ca2+], cho php xc nh [Ca2+] tan. Trong trng hp ny, ccthymocyte ( cc tbo ca thymus) bkch thch vi ATP ngoi bo, lm tng [Ca2+] bn

trong tbo. Cc tbo khng ng nht trong cc p ng ca chng; mt stbo c[Ca2+] ni bo cao ( mu ); cc tbo khc th c [Ca2+] ni bo thp hn ( xanh dng).


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(b)Khi mt mu d c sdng o [Ca2+] trong mt tbo gan n l, chng ti quanst thy agonist norepinephrine ( thm vo mi tn) gy ra nhng dao ng ca [Ca2+] t200 n 500 nM. Nhng dao ng tng tc to ra cc loi tbo khc bi cc tn hiungoi bo khc.

Calmodulin cng l mt tiu n v y ca mt h cc enzyme,Ca2+/calmodulindependent protein kinases ( CaM kinase I-IV). Khi [Ca2+] ni botng p ng vi mt vi kch thch, calmodulin lin kt vi Ca2+, tri qua mt sthay i vhnh th, v hot ha CaM kinase. Kinase sau phosphoryl ha mt senzyme ch, iu ha cc hot tnh ca chng. Casmodulin cng l mt tiu n viu ha phosphorylase b kinase ca c, c hot ha bi Ca2+.. Do Ca2+ kchthch sco c cn ATP trong khi cng hot ha sphn hy glycogen, cung cp nhinliu cho qua trnh tng hp ATP. Nhiu enzyme khc cng c bit n c iu

ha bi Ca

2+

thng qua calmodulin. ( Bng 126).

Bng 12-6. Mt sprotein c iu ha bi Ca2+v Calmodulin


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Hnh 12-21. Calmodulin. y l cht trung gian protein ca nhiu phn ng enzyme kchthch Ca2+. Calmodulin c bn vng lin kt vi Ca2+c i lc cao ( Kd 0.1 ti 1 M). (a)Mt m hnh gm nhng di cu trc tinh thca calmodulin ( PDB ID 1CLL). Bn vnglin kt vi Ca2+bchim chbi Ca2+( mu tm). Domain c ui amino bn tri; domainc ui carboxyl bn phi; (b)Calmodulin lin kt vi mt domain xon c ( mu ) ca

mt trong nhiu enzyme m n iu ha, protein kinase II ph thuc calmodulin ( PDB ID1CDL). Lu rng xon gia di c ththy r trong hnh (a)quay ra sau lin kt vidomain c cht xon. Xon trung tm linh ng khi dng dung dch hn l dng tinh th.(c)Mi vng trong bn vng lin kt vi Ca2+xy ra trong mt motif xon-cun-xon cgi l bn tay EF, cng c tm thy nhiu protein lin kt vi Ca2+khc.

TM TT 12.4

Mt hln ca cc receptor mng plasma vi by phn on xuyn mng hot ngthng qua cc G protein d lp th (heterometric). Da trn lin kt vi ligand, cc

receptor m xc tc strao i ca lin kt GTP vi GDP vi mt protein G lin kt,thc y sphn ly ca tiu n v ca protein G. Tiu n vny kch thch hocc chhot tnh ca mt enzyme lin kt vi mng thay i nng ca sn phmtruyn tin thhai ca n.

-adrenergic receptor lin kt vi epinephrine, sau qua mt protein G hot ha,Gs, hot ha adenylyl cyclase trong mng plasma. cAMP c sn xut bi adenylylcyclase l mt cht truyn tin th hai ni bo kch thch protein kinase ph thuccAMP, qua trung gian cc nh hng ca epinephrine bi s phosphoryl ha cc

protein chcht, lm thay i cc hot tnh enzyme hoc cc c im cu trc cachng.

Thc ca cc skin m mt phn tn lca hormone hot ha mt sxc tcli tip tc hot ha sxc tc khc v tip tc, kt qul skhuych i tn hiuln; y l c tnh ca phn ln cc hthng hot ha hormone.

Mt scc receptor kch thch adenylyl cyclase qua Gs; nhng receptor khc c chadenylyl cyclase qua Gi. Do [cAMP] trong tbo phn nh tn hiu u vo hp

nht ca hai ( hay nhiu) tn hiu.


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AMP vng th c bi tit bi cAMP phosphodiesterase v Gs kha n bi sthyphn ca lin kt GTP vi GDP. Khi tn hiu epinephrine vn cn, -adrenergicreceptorprotein kinase chuyn bit v arrestin 2 tm thi khtnh nhy receptor vko n di chuyn vo cc ti ni bo. Trong mt vi trng hp, arrestin cng hot

ng nh l protein nng , mang cc thnh phn protein ca mt con ng truyntn hiu li vi nhau nh l thc MAPK.

Mt vi receptor c cu trc un khc bt cp vi mt phospholipase C mngplasma tch PIP2thnh diacylglycerol v IP3. Bng vic mcc knh Ca2+trong mngli ni cht, IP3lm tng [Ca2+] trong cytosol. Diaclyglycerol v Ca2+hot ng vinhau hot ha protein kinase C, phosphoryl ha v thay i hot tnh ca cc

protein tbo chuyn bit. [Ca2+] trong tbo cng iu ha mt scc enzyme khc,thng qua calmodulin

Khung 12-2. THC NGHIM TRONG SINH HAFRET: Ha sinh hc c quan st trong mt tbo sngCc mu d pht hunh quang c sdng phbin kim tra nhanh nhng thayi sinh ha trong cc tbo sng n l. Chng c thnhn mt p ng tc thi (trong vi nano giy) da trn nhng thay i nng ca mt cht truyn tin thhaini bo hoc hot tnh ca mt protein kinase. Thm na, knh hin vi hunh quang ckh nng phn gii pht hin ra u trong t bo nhiu thay i ang xy ra.Trong mt quy trnh c sdng rng ri, cc mu d pht hunh quang c tmthy tmt protein pht hunh quang xy ra mt cch t nhin protein pht hunh

quang mu xanh lc ( GFP) ca loi saAequorea victoria( Hnh 1).

Khi bkch thch bi mt photon nh sng, GFP pht ra mt photon ( l, n phthunh quang) trong vng mu xanh lc ca quang ph. GFP l mt khoang gm 11

Hnh 1Aequorea victoria, mt loi sa cnhiu Puget Sound, Washington State.


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chui mch thng (11-stranded barrel), v trung tm hp thu/pht ra nh sng caprotein (chromophore ca n) bao gm tripeptide Ser65-Tyr66-Gly67, nm trong khoang(barrel) ( Hnh 2). Cc bin thca protein ny, vi phpht hunh quang khc nhau,c thc sn xut bi kthut gen ca gen GFP. Cho v d, protein pht hunhquang mu vng ( YFP), Ala206trong GFP c thay bi gc Lys, lm thay i di

bc sng ca shp thu nh sng. Cc bin thkhc ca phm nhum pht hunhquang mu xanh dng GFP ( BFP) hoc nh sng mu lc cam ( CFP), v mt

protein lin kt ( mRF1) pht ra nh sng ( Hnh 3). GFP v cc bin thca n lnhng cu trc rn chc vn c khnng gp thnh hnh th-barrel tnhin khign n vi mt protein khc. Cc nh nghin cu thng sdng cc protein lai phthunh quang nh l thc o quang pho cc khong cch gia cc thnh phntng tc trong mt tbo.

Mt phn tpht hunh quang bkch thch nh l GFP hay YFP c thsdng nnglng tphoton hp thu theo mt trong hai cch: (1) bi spht hunh quang, pht ramt photon c bc sng di hn ( nng lng thp hn) l nh sng bkch thch,

hoc (2) bi fluorescence resonance energy transfer ( FRET) khng pht x, trong nng lng ca phn tbkch thch ( cht cho in t) qua trc tip n mt phn tgn ( cht nhn in t) m khng pht ra mt photon, kch thch cht nhn in t( Hnh 4). Cht nhn in tc thphn r ngay n trng thi ban u bi sphthunh quang; photon c pht ra c bc sng di hn ( nng lng thp hn) nhsng bkch thch ban u v spht hunh quang ca cht cho in t. M hnh thhai ny ca sphn r ( FRET) c thchkhi cht cho in tv cht nhn in tgn vi nhau ( trong khong t1 n 50 ); hiu ng ca FRET th tng ng ngcli vi mc nng lng thsu ca khong cch gia cht cho in tv cht nhnin t. Do o nhng thay i rt nhtrong khong cch gia cht cho in tv cht

nhn in tbiu hin nh l nhng thay i rt ln trong FRET, c o nh l spht hunh quang ca phn tnhn in t khi cht cho in tb kch thch. Vi

Hnh 2Protein pht hunh quang mu xanhlc ( GFP) vi chromophore pht hunhquang thhin dng bng v gy ( cngun gc tPDB ID 1GFL)

Hnh 3Phpht hun quang ca cc binthGFP


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nhng pht hin nhy vi nh sng, tn hiu pht hunh quang ny c thc tvo nhng vng chuyn bit ca cc tbo sng ring l.

FRET c sdng o [cAMP] trong cc tbo sng. Gene ca GFP c gn vitiu n viu ha (R) ca protein kinase phthuc cAMP, v gen cho BFP gn vitiu n vxc tc (C) ( Hnh 5). Khi hai protein knc ny c biu hin trongmt tbo, BFP ( cht cho in t; bkch thch 380 nm, pht hunh quang 460nm) v GFP ( cht nhn in t; bkch thch 475 nm, pht hunh quang 545 nm)trong PKA bt hot (R2C2tetramer) gn tri qua FRET. Bt cu trong t

bo [cAMP] tng, phc hp R2C2phn ly thnh R2v 2C v tn hiu FRET mt, biv cht cho in tv cht nhn in tth qu xa cho FRET nh hng. Vic quanst trong knh hin vi, vng c [cAMP] cao c mt tn hiu GFP ti thiu v tn hiuBFP ti a. Vic o tlca spht hunh quang bc sng 460 nm v 545 nmcho mt php o nhy ca sthay i [cAMP]. Bng cch xc nh tlny cho ttccc vng ca tbo, ngi nghin cu t c th to ra mt hnh nh c mu sckhng tht ca tbo, m trong t l, hay [cAMP] tng i c biu th bicng mu. Nhng hnh nh c ghi li nhng khong thi gian pht hinnhng thay i trong [cAMP] qua thi gian.

Hnh 4Khi protein cho in t( CFP) bkch thch vi nh sng n sc c bc sng 433

nm, n pht ra hunh quang bc sng 476 nm ( tri). Khi protein ( mu ) gn vi cctng tc CFP vi protein ( mu tm) gn vi YFP, stng tc mang CFP v YFP n gnnhau cho php schuyn nng lng cng hng hunh quang ( FRET) gia chng.By gi, khi CFP hp thu nh sng 433 nm, thay v pht hunh quang bc sng 476 nm,n chuyn nng lng trc tip thnh YFP, sau pht hunh quang bc sng pht rac trng ca n l 527 nm. Tlca spht nh sng 527 nm v 476 nm do l mt

php o stng tc ca protein v tm.


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Mt bin thca cng nghny c sdng o hot tnh ca PKA trong mt tbo sng ( Hnh 6). Cc nh nghin cu to ra mt sphosphoryl ha mc tiu viPKA bng cch sn xut mt protein knc cha bn yu t: YFP ( cht nhn int); mt peptide ngn vi mt gc Ser bao quanh bi trnh tPKA; mt domain linkt vi P-Ser ( c gi l 14-3-3); v CFP ( cht cho in t). Khi gc Ser khngc phosphoryl ha, 14-3-3 khng c i lc vi gc Ser v protein knc tn titrong mt dng mrng, vi cht cho in tv cht nhn in tqu xa nhau tora mt tn hiu FRET. Bt cu trong tbo PKA th hot ng, n phosphorylha gc Ser ca protein knc, v 14-3-3 lin kt vi P-Ser. Theo cch , n koYFP v CFP li vi nhau v mt tn hiu FRET c pht hin vi knh hin vi hunhquang, pht hin sc mt ca PKA hot ng.

Hnh 5Phng php o [cAMP] viFRET. Shp nht gen to ra cc

protein knc c chFRET khi PKAiu ha v cc tiu n vxc tc

c kt hp ( [cAMP] thp). Khi[cAMP] tng, cc tiu n vtch ra, vFRET dng li. Tlca sphthunh quang 460 nm ( phn tch) v545 nm ( phc hp) do i hi mt

php o [cAMP] nhy.

Hnh 6Phng php o hot tnh caPKA vi FRET. Mt protein cu trclin kt vi YFP v CFP vi mt peptidecha mt gc Ser bao quanh bi trnh tcho s phosphoryl ha bi PKA, vdomain lin kt vi phosphoserine 14-3-3. PKA hot ng phosphoryl ha gcSer, ct bt vi domain lin kt 14-3-3,mang cc protein pht hunh quang

gn cho php FRET xy ra, pht hinshin din ca PKA hot ng.


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12.5 CC PROTEIN NNG A HNH V CC MNG MNGKhong 10% ca 30,000 n 35,000 gen bgen ngi m ha cc protein tn

hiucc receptor, cc protein G, cc enzyme to ra cc cht truyn tin thhai, ccprotein kinase ( > 500), cc protein lin quan n skhtnh nhy, v cc knh ion.

Khng phi protein tn hiu no cng c biu hin trong mt tbo nhn, nhngphn ln cc tbo cha nhiu protein. Mt protein tm thy mt tbo khc trongcon ng truyn tn hiu nh thno? V nhng tng tc ca chng c iu hanh thno? Sphosphoryl ha thun nghch ca cc gc Tyr, Ser v Thr trong cc

protein tn hiu to cc vng ct gim (docking sites) vi cc protein khc, v nhiuprotein tn hiu th ahnh ( multivalent) m chng c thtng tc vi mt viprotein khc nhau hnh thnh cc phc hp tn hiu a protein. Trong phn nychng ti trnh by mt s t v dm tcc qu trnh chung ca cc tng tc

protein trong con ng truyn tn hiu.

Cc module protein lin kt vi cc gc Tyr, Ser hay Thr c phosphoryl hatrong cc protein cng loi

Chng ta thy rng protein Grb2 trong con ng truyn tn hiu insulin ( Hnh

126) lin kt qua domain SH2 ca n vi cc protein khc cha cc gc Tyr.B gen ngi m ha t nht 87 protein cha SH2, nhiu protein c bit n

tham gia vo struyn tn hiu. Gc -Tyr c lin kt trong mt ti su trong mtdomain SH2, vi mi gc ca cc phn t phosphate oxygen tham gia vo lin kt

hydrogen hay cc tng tc in trng; cc cht mang in tch dng trn hai gcArg minh ha ni bt trong lin kt. Nhng im khc nhau rt nhtrong cu trc cacc domain SH2 nhng protein khc nhau cho nhng tnh c hiu ca cc tng

tc ca chng vi cc protein cha Tyr khc nhau. Ba n nm gc pha bn

ui carboxyl ca gc -Tyr th ti hn trong vic quyt inh tnh c hiu ca cctng tc vi cc domain SH2 ( Hnh 1222).

Cc PTB domain ( phosphotyrosine binding domains) cng lin kt vi Tyr trong cc protein cng loi, nhng cc trnh tti hn ca chng v cc cu trc

ba chiu phn bit chng tcc domain SH2. Bgen ngi m ha 24 protein chacc PTB domain, bao gm IRS 1, m chng ta gp trong vai tr nh l m t

protein nng trong struyn tn hiu insulin ( Hnh 126).


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HNH 12-22. Cu trc ca domain SH2 v s tng tc ca n vi mt gc -Tyrtrong mt protein cng loi, (PDB ID 1SHC). Domain SH2 thhin nh l mt sbiudin ng vin bmt mu xm. Phospho ca nhm phosphate trong -Tyr tng tc thhin nh l mt khi cu mu cam, phn ln gc th c mu ti trong hnh ny. Mt st gcktip hng n ui carboxyl ca protein cng loi thhin mu . Domain SH2 tngtc vi -Tyr ( nh l gc c phosphoryl ha, c quy cho vtr 0) v cng vi ba gc ktip hng n ui carboxyl (phc ha +1, +2, +3). Cc gc th quan trng trong gc -Tyrc bo tn trong tt ccc domain SH2. Mt vi domain SH2( Src, Fyn, Hck, Nck) lmcho cc gc tch in m cc vtr +1 v +2; cc domain khc ( PLC-1, SHP-2) c mt

khe knc chn cc gc cht bo cc vtr +1 v +5. Nhng khc bit ny nh r ccphn lp ca cc domain SH2 c nhng tnh c hiu cng loi khc nhau.

Nhiu protein kinase tn hiu, bao gm PKA, PKC PKG v cc thnh vin cathc MAPK, phosphoryl ha cc gc Ser hay Thr trong cc protein ch, trong mt vitrng hp t c khnng tng tc vi cc protein cng loi qua gc c

phosphoryl ha, bt u mt qu trnh xui dng. Mt soup c bn ca cc domain

lin kt vi Ser hay -Thr c xc nh, v snhiu chc chn c lin kt.Mi domain ng h mt trnh t xung quanh gc c phosphoryl ha, v th cc

domain biu din cc hca cc vng c cng nhn chuyn bit cao, c thlin ktvi mt tp hp cc protein c phosphoryl ha.

Trong mt vi trng hp, protein gn vi domain th nm bn trong. Sphosphoryl ha mt scc protein kinase c chhot tnh ca chng bng cch btr

s tng tc ca mt domain SH2 vi mt -tyr trong domain khc ca enzymetng t. Cho v d, protein Tyr kinase Src ha tan, khi bphosphoryl ha trn mtgc Tyr ti hn, bbt hot nh l mt domain SH2 cn gn vi protein c cht thay

v gn vi mt -Tyr bn trong ( Hnh 1223). Glycogen synthase kinase 3 ( GSK3)

bbt hot khi phosphoryl ha mt gc Ser trong domain c chca n. ( Hnh 1223b). S dephossphoryl ha ca gc m domain gii phng enzyme lin kt v


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phosphoryl ha cc protein mc tiu. Tng t, nhm u phn cc ca phospholipidPIP3 nh ra tvng bn trong ca mng plasma, cung cp cc u thu ht cc proteincha SH3 v cc domain khc.

Phn ln cc protein lin quan n struyn tn hiu mng plasma c mt haynhiu protein hay phospholipid lin kt vi cc domain; nhiu domain c ba hay nhiuhn cc protein, v do a hnh trong cc tng tc vi cc protein tn hiu khc.Hnh 1224 thhin mt st nhiu protein a hnhc bit tham gia vo struyntn hiu.

Mt bc tranh ng ch ca cc con ng truyn tn hiu hin ra t ccnghin cu ca nhiu protein truyn tn hiu khc v chng cha nhiu domain linkt ( Hnh 12-25). Mt tn hiu ban u l kt qu trong s phosphoryl ha careceptor hay protein ch, khi u skt hp ca cc phc hp a protein ln, gnvi nhau trn ccprotein nng c hnh thnh tcc protein adaptor vi cc sccha lin kt a hnh. Mt sphc hp ny c mt s protein kinase hot ha mi

protein khc, to ra mt thc ca sphosphoryl ha v mt skhuch i ln cc tnhiu ban u. Cc tbo ng vt cng c phosphotyrosine phosphatase ( PTPases),

loi b phosphate t cc gc -Tyr, o ngc nh hng ca s phosphoryl ha.Mt vi phosphatase ny l cc receptor nh cc protein mng, c kim sot bicc nhn tngoi bo khng xc nh.; cc PTPase khc ha tan v cha cc domainSH2. Thm vo , cc t bo ng vt c cc protein phosphoserine v

phosphothreonine phosphatase, o ngc cc nh hng ca cc protein kinasechuyn bit Ser v Thr. Chng ta c ththy, sau , struyn tn hiu xy ra trongcc mng protein; c kim sot treceptor tn hiu p ng vi cht tc ng vc thct ngay tc khc bng cch thy phn mt lin kt phosphate ester n l.


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HNH 12-23. C chca sc chtng ca Src Tyr kinase v GSK3. (a)dng hotng ca Src kinase, mt domain SH2 lin kt vi mt -Tyr trong c cht, v mt domainSH3 lin kt vi mt vng giu proline ca c cht, gn vng hot ng ca kinase vi mtsgc Tyr mc tiu trong ccht. Khi Src c phosphoryl ha trn mt gc Tyr chuyn

bit, domain SH2 lin kt vi -Tyr bn trong thay v vi -Tyr ca c cht, ngn cn slin kt ca kinase vi c cht protein ca n; do enzyme bc ch tng. (b)Trongglycogen synthase kinase 3 ( GSK3) bc chtng, mt gc -Ser bn trong lin kt vimt domain lin kt -Ser bn trong ( trn cng). S kh phoshoryl ha ca gc Ser bntrong ny ri khi vng lin kt -Ser ca GSK3 c sn lin kt vi -Ser trong mt c

cht protein v do n vtr kinase phosphoryl ha gc Ser ln cn ( di cng).


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HNH 12-24. Mt smodule lin kt ca cc protein truyn tn hiu.Mi protein cbiu hin bi mt ng ( vi ui amino bn tri); cc k tcho thy vtr ca cc domainlin kt c bo tn ( vi nhng c trng c lit k trong vtr then cht; pH biu thtnh tng ng phc tp; cc chvit tt khc c gii thch trong on vn); nhng khungmu xanh lc biu thnhng hot tnh xc tc. Tn ca mi protein c gn cui uicarboxyl ca n. Nhng protein truyn tn hiu ny tng tc vi cc protein c

phosphoryl ha hay cc phospholipid trong nhiu hon vv cc hp cht hnh thnh ccphc hp truyn tn hiu ng nht.

Tnh a hnh ca cc protein truyn tn hiu cho php skt hp ca nhiu hp cht

khc nhau ca cc module tn hiu, mi hp cht c lph hp vi cc tn hiu ringbit, cc loi tbo v cc qu trnh bin dng. Mt slng ln cc protein kinasev cc domain lin kt vi phosphoprotein ca cc kinase, mi kinase vi tnh chiu ring ca n ( trnh tng nht cn cho c cht ca n), cung cp nhiu hpcht v nhiu vtr truyn tn hiu khc nhau ca sphc tp bt thng. V nhiu

phosphatase chuyn bit o ngc hot ng ca cc protein kinase, mt vi loichuyn bit ca skim sot bn trong, mt tbo c thnhanh chng khng ktni vi vng protein tng thca mt con ng truyn tn hiu. Cc c chny traomt sc cha ln vi siu ha tbo p ng vi cc tn hiu ca nhiu loi.


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Cc mng mng ( membrane rafts) v caveolae c thcch ly cc protein truyntn hiu

Cc mng mng ( membrane rafts) l cc vng ca mng i giu ccsphingolipid, sterols, v cc protein bao gm nhiu protein gn vi lp i bi GPIanchors ( chng 11). Mt sreceptor Tyr kinase nh l cc receptor vi cc nhn ttng trng biu b ( EGF), xut hin bkhoanh vng trong cc mng; cc proteintruyn tn hiu khc nh l G protein Ras ( c prenyl ha), v heterotrimeric G

protein Gs( cng c prenyl ha trn cc tiu n v v ), th khng b khoanhvng. Bng chng tng trng cho thy sc lp cc protein truyn tn hiu th quantrng vmt chc nng. Khi cholesterol c loi btcc mng bng cch xl vicyclodextrin ( lin kt vi cc cholesterol v loi bn tmng), nhng mng th b

ph vv mt scon ng truyn tn hiu trnn khim khuyt.

Skhoanh vng trong cc mng nh hng n struyn tn hiu thng qua mtreceptor nh thno? C mt skhnng. Nu mt receptor Tyr kinase trong mtmng c phosphoryl ha v phosphotyronsine phosphatase o ngc s

phosphoryl ha ny trong mng khc, sau skhphosphoryl ha ca Tyr kinase schm hoc bngn cn. Nu hai protein truyn tn hiu phi tng tc vi nhau trongsut struyn tn hiu, khnng va chm ca cc protein ny tng cao nu chai trong cng mt mng. Cc tng tc gia cc protein nng c thmnh komt mng vo mt protein truyn tn hiu thng thng khng c khoanh vng

hoc mnh ko cc receptor ra ngoi mt mng. Cho v d, EGF receptortrong cc nguyn bo si b cch ly thng thng c tp trung trong cc mngchuyn bit c gi l caveolae ( xem hnh 11-21). Nhng x l vi EGF lm choreceptor ri khi mng. Sdi chuyn ny phthuc vo hot tnh protein kinase careceptor, cc receptor t bin thiu hot tnh ny vn cn trong cc mng trong sutqu trnh x l vi EGF, Caveolin, mt protein mng ton vn khoanh vng trongcaveolae, bphosphoryl ha trn cc gc Tyr p ng vi insulin v sphosphorylha c thcho php EGF receptor c hot ha ko cc receptor lin kt vi n vomng. Cui cng, mt v dkhc vstp hp ca cc protein truyn tn hiu trong

cc mng l -adrenergic receptor. Recceptor ny c cch ly trong cc mng mngcng cha cc protein G, adenylyl cyclase, PKA, v mt protein phosphatase chuyn

bit, PP2, cung cp mt n vtruyn tn hiu hp nht. Scch ly trong khng gianca cc protein truyn tn hiu trong cc mng thm chiu khc vo cc qu trnh phchp bt u bi cc tn hiu ngoi bo.


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HNH 12-25. Shnh thnh insukin ca cc phc hp truyn tnh hiu siu phn t.Lin kt ca insulin vi receptor ca n to ra mt chui cc skin dn n shnh thnhca cc phc hp lin kt vi mng lin quan n 12 protein truyn tn hiu c thhin y cng nh cc protein truyn tn hiu khc. Sphosphoryl ha ca cc gc Tyr trongreceptor insulin bt u shnh thnh phc hp, v skhphossphoryl ha ca bt kcc

protein phospho no bgy vng lin kt. Bn loi tng tc chung giphc hp vi nhau:lin kt ca mt protein vi mt phosphoprotein thhai thng qua cc domain SH2 hay PTB loi u tin ( mu ); lin kt ca cc domain SH3 trong loi u tin vi cc domaingiu proline loi thhai ( mu cam); Lin kt ca cc domain PH trong mt protein vi

phospholipid PIP3 trong mng plasma ( xanh da tri); hay slin kt ca mt protein (RAS)vi mng plasma thng qua mt lipid lin kt vi protein ( mu vng). Hai protein thhin y khng c m t trong on vn: 14-3-3, lin kt mt -Ser trong Raf v qua trunggian tng tc ca n vi MEK v MP1; mt protein nng tht cht cc lin kt gia Raf,MEK v ERK.

TM TT 12.5

Nhiu protein truyn tn hiu c cc domain gn vi cc gc Tyr, Ser hoc Thr cphosphoryl ha trong cc protein khc; tnh c hiu lin kt cho mi domain cxc nh bi cc trnh tni lin gc chc c phosphoryl ha.

Cc domain SH2 v PTB lin kt vi cc protein cha cc gc P-Tyr; cc domain

khc lin kt vi cc gc -Ser v -Thr trong cc trng hp khc nhau.

Cc domain tng ng phc tp lin kt vi phospholipid mng PIP3.


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Nhiu protein truyn tn hiu th a hnh, vi mt scc module lin kt khc nhau.Bng skt hp cc tnh c hiu c cht ca cc protein kinase khc nhau vi cctnh chuyn bit ca cc domain lin kt vi cc gc Ser, Thr ho Tyr c

phosphoryl ha v vi cc phosphatase c thbt hot nhanh mt con ng truyn

tn hiu, cc tbo to ra mt slng ln cc phc hp truyn tn hiu a protein.

Cc mng mng v cc nhm cch ly caveolae ca cc protein truyn tn hiu trongcc vng nh ca mng plasma, lm tng s tng tc ca chng v gip cho victruyn tn hiu hiu quhn.

12.6 STRUYN TN HIU VI SINH VT V THC VT

Chng ta ni rt nhiu vstruyn tn hiu cc m ng vt hu nh hoccc tbo nui cy tm. Vi khun, cc vi sinh vt nhn thc v thc vt c mch

u phi p ng vi nhiu tn hiu bn ngoi khc nhau nh O2, cht dinh dng,nh sng, cht c, By gichng ta hy tm hiu vcc c chtruyn tn hiu vi sinh vt v thc vt.

Struyn tn hiu vi khun dn n sphosphoryl ha trong mt hthng 2thnh phn

E. coli p ng vi mt sthnh phn dinh dng trong mi trng, nh ng,acid amin, bng cch bi n , c y bng mt hoc mt sroi. Mt hproteinmng c cc vng gn bmt bn ngoi mng plasma i vi cc cht hp dn chiu (ng hoc acid amin) (Hnh 12-26). S gn ligand lm cho mt vng khc(cng mt ngoi mng plasma) t phosphoryl ha ti gc Histidine. ReceptorHistidine kinase l thnh phn th nht trong h thng 2 thnh phn. Receptor Hiskinase sau xc tc cho schuyn gc phosphate tgc His n mt gc Asp trnmt protein ha tan th2, l thnh phn iu ha p ng; phosphoprotein ny dichuyn ti gc ca roi, mang tn hiu treceptor mng. Roi c iu kin bi mtmotor quay, c thy tbo i trong mi trng hoc lm cho dng li, iu phthuc vo hng quay ca motor. Thng tin treceptor cho php tbo quyt nh li n hay trnh xa cht hp dn. Nu sdi chuyn ca n l i n cht hp dn ththnh phn iu ha p ng ra tn hiu cho tbo tip tc di chuyn theo mt ngthng; nu sdi chuyn ca n l trnh xa cht hp dn th tbo sxoay li ngay lp

tc v chn mt hng mi. Slp li hnh vi ny to ra mt hng i ngu nhin,chch vi hng di chuyn theo hng nng cht hp dn tng.

E. coli khng nhng pht hin ng v acid amin m cn cO2, nhit khcnghit v cc yu tkhc na ca mi trng da vo hthng hai thnh phn ny.Hthng hai thnh phn ny c pht hin nhiu loi vi khun khc, gm cc vikhun G(+), G(-) v ckhun cng nh cc ng vt nguyn sinh v nm. R rngl c chtruyn tn hiu c pht trin rt sm trong qu trnh tin ha t bo vc bo tn.

Nhiu hthng truyn tn hiu c tbo ng vt sdng cng tng tnhcc sinh vt nhn s. Do ton b trnh tbgen rt a dng nn vi khun trnnc bit n nhiu, cc nh khoa hc khm ph ra cc gen m ha ra cc proteintng tprotein Ser hoc Thr kinase, cc protein ging Ras c iu ha bng cch


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gn vi GTP, v protein c vng SH3. Khng thy cc receptor Tyr kinase vi khun,nhng cc gc P -Tyr th vn hin din trong mt sprotein ca vi khun, do , chchn c mt enzyme no phosphoryl ha cc gc Tyr.

HNH 12-26 C chhot ng truyn tn hiu hai thnh phn vi khun.

Khi mt ligand cht hp dn (A) gn vo vng receptor ca receptor gn mng, mtprotein His kinase pha tbo cht (thnh phn 1) c hot ha v tphosphoryl

ha ti gc His. Nhm phosphoryl ny sau chuyn n mt gc Asp trn thnhphn th 2 (trong vi trng hp l mt protein ring bit, cn li l domain careceptor protein). Sau khi phosphoryl ha Asp, thnh phn 2 di chuyn n gc roi,ti xc nh hng quay ca motor roi.

Cc hthng truyn tn hiu thc vt c mt sim ging nh vi sinh vt vng vt hu nh

Ging nh ng vt, thc vt c mch c cc phng tin lin lc gia cc m cn bng v sinh trng pht trin thng; thch nghi vi cc iu kin mitrng nh O2, cht dinh dng, nh sng, nhit ; v cnh bo c shin din

ca cc cht c v mm bnh gy hi (hnh 12-27). Phi tri qua t nht 1 tnm tinha, khi cc nhnh thc vt v ng vt c phn ra teukaryote phn nh cskhc bit trong cc c chtruyn tn hiu: mt sc chthc vt c bo tnv ging nh ng vt (cc protein kinase, cc protein khung, cc nucleotide vng,cc bm ion sinh in, v cc knh ion c kim sot bi cng); mt sli ging vicc hthng truyn tn hiu hai thnh phn ca vi khun; v mt sli chc duy nht thc vt (v d nh cc c ch cm nhn nh sng) (Bng 12-7). B gen caArabidopsis thaniana c nghin cu rt k, n m ha khong 1000 protein Ser/Thrkinase, gm khong 60 MAPKs, v gn 400 cc receptor kinas lin kt mng c chcnng phosphoryl ha gc Ser hoc Thr; rt nhiu protein phosphatase; cc protein

khung a cc

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12. Biosignaling