Heme proteins are ubiquitous in nature. Their function is determined by the surrounding protein structure and coordination environment. Here, we explore the ability to tune the local electronic environment of the heme molecule in a self-assembled peptide fibril. The peptide c16-XHL3K3-CO2H has been shown to self-assemble into nanofibers and has demonstrated the ability to bind both naturally occurring heme molecules as well as zinc metalloporphyrins. By varying the amino acid closest to the hydrophilic core (c16) we have displayed the ability to tune the local coordination environment. Three peptides will be highlighted with varying coordination environment where X = Ala, His, or Met in the peptide c16-XHL3K3-CO2H. The alanine variant was designed to offer a five coordinate environment that we have employed in the past.  It yields a potential mixture of mono-His and bis-His axial ligation around the iron(III) metal center. The methionine 'mutant' presents a potential cytochrome c like environment that would have potential application in electron transfer. It is the only system that yields a purely high-spin coordination environment. Finally, the histidine variant yields a bis-His environment. Various spectroscopies (UV/vis, Raman, EPR) indicate a predominately low-spin, bis-His coordinated heme environment. Interestingly, in each self-assembled peptide system when the heme is reduced, only the bis-His axially ligation achieves reversible oxidation. The His-Ala and His-Met coordination modes result in an irreversible oxidation. We propose that the bis-His axial ligation yields an environment suitable for reversible oxygen binding as evidenced by preliminary UV/visible spectroscopic studies. Such an achievement has been made with coiled-coil peptide bundles where this is the first example in a �-sheet environment from a much smaller peptide. Self-assembly of the small peptide can be employed to produce the necessary coordination environment for binding the heme molecule.

Self-assembled heme peptides: Modulating function through coordination environment

248th National Meeting (2014)

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