Redox Linked Coordination Change In OmcA: Implications for Dissimilatory Fe(III) Reduction
Fe K-XANES and EXAFS spectra for oxidized OmcA showed evidence for a sorption induced change in the coordination environment of heme Fe. Similar to our results for the equine mono-heme cytochrome c, the heme Fe coordination of sorbed OmcA was similar to the denatured OmcA. Denatured oxidized OmcA however, disintegrated, based on its XANES and EXAFS spectral similarities to Fe metal foil. OmcA behavior was markedly different from the behavior of the equine cytochrome c which, on denaturation changed from its native his-met ligation to a bis-his ligation. Based on XANES and EXAFS spectral similarities of sorbed oxidized OmcA with denatured OmcA, our results indicate that oxidized OmcA is not designed to interact with metal-oxide minerals. If OmcA is indeed the electron shuttle to metal-oxide surfaces, we expect reduced OmcA to sorb readily in order to transfer electrons; similarly, the oxidized OmcA should be designed to desorb. Fe K-XANES and EXAFS spectra for dissolved OmcA showed redox linked changes. suggesting that the sorption behavior of reduced and oxidized OmcA would differ consistent with the demands of its role in dissimilatory Fe(III) reduction.