Engineering Self-Assembling Peptides

to Tune the Coordination Environment

of MetalloporphyrinsJacob Kronenberg, Illinois Mathematics and Science Academy

Advisor: Dr. H. Christopher Fry, Argonne National Laboratory

Background: c16-AHL3K3-CO2H

A self-assembling metalloporphyrin-binding peptide amphiphiles, developed by

Fry et al. (2012). It uses a monohistidine binding site to coordinate hemes.

Natural Porphyrin-Binding

Proteins

These three natural proteins each have different coordination environments, as shown below.

Nitrophorin Myoglobin Cytochrome-c

Focusing Question

How can we design a peptide to control the

coordination environment of a bound porphyrin

and thus tune its electrochemical or catalytic

properties?

Designed peptides

c16-AHL3K3-

CO2H

c16-H2L3K3-

CO2H

c16-MHL3K3-

CO2H

β-Sheet Formation

-40000

-20000

0

20000

40000

60000

80000

100000

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140000

190 200 210 220 230 240 250

Cir

cu

lar

Dic

hro

ism

(de

g·c

m^

2/m

mo

l)

Wavelength (nm)

Circular Dichroism Spectra

c16-AHL3K3-CO2H

c16-H2L3K3-CO2H

c16-MHL3K3-CO2H

Circular dichroism spectra of the three peptides demonstrate β-sheet

formation. All three demonstrate the peaks characteristic of β-sheets, with the

differences in strength believed to be due to variations in bundling.

Spectra of Porphyrin-Peptide

Complexes

Fig. 2: Sample Ultraviolet-Visible spectra of the three peptides, each bound to

oxidized hemin. The inset shows the Q-band peaks with greater detail.

0

0.2

0.4

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0.8

1

300 400 500 600 700 800

Ab

so

rba

nc

e

Wavelength (nm)

UV-Vis Spectra

Electron Paramagnetic

Resonance

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Sig

na

l

Magnetic Field (G)

Electron Paramagnetic Resonance Spectra

c16-AHL3K3-CO2H

c16-H2L3K3-CO2H

c16-MHL3K3-CO2H

High Spin

Low Spin

High Spin

These EPR spectra show that c16-MHL3K3-CO2H shows a characteristic

high-spin pattern, c16-H2L3K3-CO2H shows a low-spin pattern, and c16-

AHL3K3-CO2H exhibits a weaker, but still low-spin pattern.

Atomic Force Microscopy

Bundle Network Structure Single Bundle Structure

Photo credit to Dr. Seth Darling and Dr. Adina Luican-Mayer

O2 Binding

0.0

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0.9

1.2

1.5

1.8

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Ab

so

rba

nc

e

Wavelength (nm)

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Fe(III)

Fe(II)

Fe(II) + O2

Fe(II) + N2

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300 400 500 600 700 800A

bs

orb

an

ce

Wavelength(nm)

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500 600 700

c16-AHL3K3-CO2H c16-H2L3K3-CO2H

The UV/vis spectra for the His and His-His peptides show that chemical

oxidation and reduction change the electron environment and that they can bind

O2.

Conclusions

All three peptides, c16-AHL3K3-CO2H, c16-H2L3K3-CO2H, and c16-MHL3K3-CO2H self-assemble into high-aspect-ratio fibers.

The His and His-His coordination environments yield low-spin hemes.

The His-Met environment yields high-spin hemes.

Each peptide does give a unique coordination environment

Results suggest that c16-H2L3K3-CO2H (his-his environment) can reversibly bind O2.

Discussion

The bishistidine peptide has similar properties to other natural proteins, including coordination environment, low-spin state, and reversible O2

binding.

The other two peptides have new properties which require further testing.

These materials could have applications as chemotherapeutic agents.

Possible further research includes testing the interactions of the peptides with cells and further examining the coordination environments, particularly with the monohistidine peptide.

Selected Bibliography

Cochran, F., Wu, S., Wang, W., Nanda, V., Saven, J., Therien, M., & DeGrado, W. (2005). Computational de novo design and characterization of a four-helix bundle protein that selectively binds a nonbiological cofactor. J. Am. Chem. Soc., 127, 1346- 1347.

Fry, H., Garcia, J., Medina, M., Ricoy, U., Gosztola, D., Nikiforov, M., Palmer, L., & Stupp, S. (2012). Self-assembly of highly ordered peptide amphiphilemetalloporphyrin arrays. Journal of the American Chemical Society, 134(26), 14646-9.

Hartgering, J.D., Beniash, E., & Stupp, S. I. (2001). Self assembly and mineralization of peptide-amphiphilenanofibers. Science, 294, 1684-1687.

More sources available upon request.

Acknowledgments

I would like to thank Dr. Christopher Fry for his help and

guidance with this project; Dr. Tijana Rajh, Dr. Adina

Luican-Mayer, and Dr. Seth Darling for their assistance

with the use of instrumentation; the Argonne National

Laboratory’s Center for Nanoscale Materials, for

allowing use of their facilities; and the SIR team of

IMSA, for making this program possible.

Questions?