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Engineering Self-Assembling Peptides to Tune the Coordination Environment of Metalloporphyrins The document discusses how self-assembling peptides can be designed to control the coordination environment of bound metalloporphyrins and tune their properties. Three peptides were designed with different metal-binding sites: one with a single histidine, one with two histidines, and one with a histidine and methionine. Spectroscopic analysis showed the single histidine and double histidine peptides bound heme in a low-spin state while the histidine-methionine peptide bound it in a high-spin state. Furthermore, the double histidine peptide could reversibly bind oxygen like natural proteins.
ANL Presentation
- 1. Engineering Self-Assembling Peptides to Tune the Coordination Environment of Metalloporphyrins Jacob Kronenberg, Illinois Mathematics and Science Academy Advisor: Dr. H. Christopher Fry, Argonne National Laboratory
- 2. 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.
- 3. Natural Porphyrin-Binding Proteins These three natural proteins each have different coordination environment s, as shown below. Nitrophorin Myoglobin Cytochrome-c
- 4. 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?
- 6. β-Sheet Formation -40000 -20000 0 20000 40000 60000 80000 100000 120000 140000 190 200 210 220 230 240 250 CircularDichroism(deg·cm^2/mmol) 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.
- 7. 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 0.6 0.8 1 300 400 500 600 700 800 Absorbance Wavelength (nm) UV-Vis Spectra
- 8. Electron Paramagnetic Resonance -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 1000 2000 3000 4000 5000 Signal 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.
- 9. Atomic Force Microscopy Bundle Network Structure Single Bundle Structure Photo credit to Dr. Seth Darling and Dr. Adina Luican-M
- 10. O2 Binding 0.0 0.3 0.6 0.9 1.2 1.5 1.8 300 400 500 600 700 800 Absorbance Wavelength (nm) 0.0 0.1 0.2 0.3 500 600 700 Fe(III) Fe(II) Fe(II) + O2 Fe(II) + N2 0 0.3 0.6 0.9 1.2 1.5 1.8 300 400 500 600 700 800 Absorbance Wavelength(nm) 0 0.1 0.2 0.3 500 600 700 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.
- 11. 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.
- 12. 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.
- 13. 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 amphiphile metalloporphyrin 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-amphiphile nanofibers. Science, 294, 1684-1687. More sources available upon request.
- 14. 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.
- 15. Questions?