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Glycosides and Glycosidases
1. Definition
2. Examplesb. Isoprenoid glycosides
- aroma- sweeteners- medicines- molecular biological reagent- anti-fungal saponins- intermediates to primary andsecondary metabolites
(u) (u)
061109
a. Phenylpropanoid glycosides
c. Glucosinolates
d. Indigo
e. Cyanogenic compounds
3. Summary
• Polymer (structure)
Glycosides of phytohormones (auxin, cytokinin),
Isoprenoids, Alkaloids
Phenylpropanoids
Glucosinolates, Cyanogenic glucosides, etc..
• Conjugates (non-structure)
To protein GlycoproteinsTo other chemicals
e.g., Cellulose..(Most abundant chemical on earth)
To nucleotides e.g., ADP-glucose, UDP-glucose
Carbohydrates in Plants
R X Aglycone
N (N-X-S/T); O (S/T)( ER membrane, Golgi)
Glycone
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X = O, N, S, none
R (+OH):
1
2
3
45
6
-Glucose
O
OH
OH
OH
-Rhamnose
O
OHOH
OH
OH
OH
O
OH
OH
OH
OH
OH
-Galactose
Anomeric carbon
R X
“Glycoside”
Aglycone
R X
R-OH
HX
Aglycone
NDP-R
Glycoside
Glycosidase
Glycosyltransferase
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-Glucosidase
O-Glc
NO2
OH
NO2
Abs at 420nm
3. “Substrate specificity”
1.Almond emulsin:
used to determine structure of glycosides
2. Can be detected with a commercially available
substrate
Glycosides and Glycosidases
1. Definition
2. Examplesb. Isoprenoid glycosides
- aroma- sweeteners
- medicines- molecular biological reagent- anti-fungal saponins- intermediates to primary andsecondary metabolites
(u) (u)
a. Phenylpropanoid glycosides
c. Glucosinolates
d. Indigo
e. Cyanogenic compounds
3. Summary
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OH
R1
R2
R3Isoprenoid glycosides
R1 R2 R3
O-Glc-GlcO-Glc-GlcO-Glc-Glc
O-Glc-GlcO-Glc-AraO-Glc
H
HH
OHOH
O-GlcO-Glc-Rha
OH O-Glc-Rha
OH O-Glc-Rha
O-GlcOHO-GlcOH
Protopanaxadiol saponins
Protopanaxatriol saponins
Panax ginseng
Cardiac glycosides
O
O O
OH
O
OH
O
OH
OO
OH
OOH
Digitoxin
O
O O
OH
O
OH
O
OH
OO
OH
OOH
OH
Digoxin
Digitoxigenin
Digoxigenin
Isoprenoid glycosides
Digitalis purpurea
(Foxglove)
(DIG)digitoxose
Inhibit the membrane bound Na+-K+-ATPase pump
Increase contraction (+ inotropic effect)
of the heart
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Dioscorea spp. (wild yam)
https://reader012.{domain}/reader012/html5/0808/5b6a18f201c5c/5b6a18f8bc955.jpg
http://www.rain-tree.com/Plant-Images/dioscorea-pic.htm
O
O
OH Diosgenin
O
O
Progesterone
Isoprenoid glycosides
O
O
R1O
O
R1O
O
Glc
OH
Furostanol glycosides
(in fresh plants)
Spirostanol glycosides
(in harvested plants)
R1 = mono- or oligosaccharide
Antifungal activity“Harmless”
Isoprenoid glycosides
Furostanol glycosde 26-O-β-glucosidase (F26G)
O
O
OH Diosgenin= “Saponin activating enzyme in plants”
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Isoprenoid glycosides
1
5
67
8
4
Substrates
Enzyme
O
O
R1O
O
R1O
O
Glc
OH
Isoprenoid glycosides
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O
O
N
O
CHO
OH
CH2OH
O AraGlc
Glc Avenacin
Avenacinase
Bowyer et al., ’95 Science 267:371-374
Ggt, Gaeumannomyces graminis var. tritici
Gga, Gaeumannomyces graminis var. avenae
Isoprenoid glycosides
Alkaloid glycosides
= “Saponin INactivating enzyme in fungi”
Most steroid glycosides (saponins)
are believed to exist in vacuolesO
O
R1O
OH
R1
R2
R3
H
H
H
O
O
O
OHO
OH
OHOH
OH
HOOC
COOH
O
O O
OH
O
OH
O
OH
OO
OH
OOH
OH
Isoprenoid glycosides
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Glc-O
OH
OH
Isoprenoid glycosides
UDP-GlcUDP
Sterols = membrane components
cholesterol
β-sitosterol
Also in membrane..
(plasma membrane)
One form of phytosterols
OO
OH
OH
OH OH
O
OH
OH OHOHO
O
OH
OH OH
OO
OH
OH
OH OHn
Peng et al., ’02 Science 295:147-50
Read and Bacic ’02 Science 295:59-60
Isoprenoid glycosides
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O
O-Glc
NHNH H H
HO
O
O
O-Glc
H
H
HO
O
O
Secologanin
(monoterpene)
Strictosidine
Isoprenoid glycosides
NH
NH2
tryptamine
Alkaloid glycosides
STR(Strictosidine synthase)
N
N
CO2CH
3
H
OHCH
3
OCH2CH
3MeO
Vindoline
NH
N
CO2CH
3
H
Tabersonine
O
O-Glc
NHNH H H
HO
O
Strictosidine
NH
N
CO2CH
3
H
NHNH H H
HO
O
CHO
CHO
N+
NH H
HO
O OHO
OH
NHNH H H
HO
O
CO2CH
3
N
NH
Tabersonine
16-hydroxytabersonine
NH
N
CO2CH
3
H
OHVindoline
4,21-dehydro-geissoschizine
Various indole alkaloids
SGD
T16H
Isoprenoid glycosides Alkaloid glycosides
(Strictosidine β-glucosidase)
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Vacuole
Nucleus
Chloroplast
Golgi body
Cell wall Plasma membrane
Mitochondrion
Peroxisome
Buchanan et al. (2000) Biochemistry & Molecular Biology of Plants
Endoplasmic
reticulum
Strictosidine
T16HSGD
STR
Young leaves
Glycosides and Glycosidases
1. Definition
2. Examplesb. Isoprenoid glycosides
- aroma- sweeteners
- medicines- molecular biological reagent- anti-fungal saponins- intermediates to primary andsecondary metabolites
(u) (u)
a. Phenylpropanoid glycosides
c. Glucosinolates
d. Indigo
e. Cyanogenic compounds
3. Summary
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R S C N
R N C S
R C N
S
N
O
NH
S
Glucosinolates
Myrosinase (thio-glucosidase)
C
NO
S Glu
SO3-
R
CN
O
SH
SO3-
R
Isothiocyanate
(mustard oils)
Nitrile
woad
Wild indigo
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R'C
R O-Glc
CN
R'C
R OH
CN
R'
CR
O HCNSH
HOOCNH
2
HOOCNH
2
CN
HOOCNH
2
CONH2
HOOCNH
2
COOH
Cyanoalaninesynthase
Cyanogenic glycosides
cyanohydrin
HCN
CH O
CN
Glc O Glc
CH O
CN
Glc
Amygdalin
PrunasinMandelonitrile
CH OH
CN
CHO
Benzaldehyde
AH
PH
MDL
..Not so specific..
..Abundant...(5-10% of soluble proteins in seed)
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Immunoblot
Enzyme => Procambium cells Substrate =>
Cotyledonary parenchyma
Poulton and Li, ‘94
+ indican
Tissue printing on nitrocellulose
+ almond
β -glucosidase
Where are the enzyme and the substrate?
+ amygdalin
Hg++ + 2CN-
Hg (ppt) + Hg(CN)2
Cyanogenic glucosides in Hevea
Linamarin Linustatin
CH3
CCH
3 O
CN
Glc O Glc
CH3
CCH
3 O
CN
Glc
Cotyledons
Endosperm
Fully-grown,
immature seed Mature seedSelmar, ‘95
Linamarase
(in apoplast)
HCN
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Cyanogenic glucosides in Hevea
CH3
CCH
3 O
CN
Glc O Glc
Linustatin
Asparagine
Linustatin
*Linamarasein apoplast
Diglucosidase
14C-labeling
CH3
CCH
3 O
CN
Glc
Cyanoalanine
synthase
*Non-specific Selmar, ‘95
*
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Glycosides and Glycosidases
1. Definition
2. Examplesb. Isoprenoid glycosides
- aroma- sweeteners- medicines- molecular biological reagent- anti-fungal saponins- intermediates to primary andsecondary metabolites
(u) (u)
a. Phenylpropanoid glycosides
c. Glucosinolates
d. Indigo
e. Cyanogenic compounds
3. Summary
-Glucosidases
• Substrate specificity
• Monocot vs. Dicot
Glycosylation
Expression
Location
Transit peptide
Signal peptide
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R X
*Not necessary for alkaloids
R-OH
HX
Aglycone
UDP-R
Glycoside
Glycosidase
Toxicity?
Hydrophobicity?
Reactivity?
Compartmentalization
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