COLLABORATIVE RESEARCH: Redox metallo-proteins and conformational gating in electron transfer to ferric minerals

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This collaborative project between researchers at the University of Wyoming and Idaho State University will examine the transfer of electrons from mineral oxide surfaces to c-type cytochromes from the cell membranes of metal-reducing microbes. Oxide interactions with iron-sulfur proteins and other biomolecules will also be investigated. The main hypothesis under investigation is to see if oxide surfaces "trigger" conformation changes in proteins on mineral surfaces that can result in a shift in the redox potential of the protein that favors electron transfer. This study was motivated because metal reducing microorganisms and how they interact with their environment are of great interest not only because they are involved in the global redox cycling of iron and other metals, but also because they are able to chemically immobilize a variety of toxic metals in the environment, including radionuclides. Research will be carried out with commercially available proteins, as well as proteins purified from metal-reducing bacteria in the laboratory. Sorption studies to understand the aqueous conditions under which optimal protein-mineral interaction happen will be conducted. The research will examine outer membrane protein adsorption to hematite and goethite as a function of pH, ionic strength, time, temperature and phosphate composition. The redox state of proteins in the adsorbed state under different geochemical conditions will also be examined. Surface imaging techniques and characterizations such as atomic force and scanning tunneling electron microscopy will be carried out as will XANES, EXAFS, and UV-VIS spectroscopy. Second harmonic generation will be used to examine the orientation of selected molecules adsorbed to oxide surfaces. Changes in the redox properties of the proteins under investigation will be correlated with conformational changes, and the polarizability of the adsorbed molecules and dimensions of the molecules in the adsorbed state will be determined. Broader impacts of this study include the scientific basis for development of protein-functionalized electrodes that will allow us to utilize the specific function of proteins in sensor applications, bioremediation strategies for toxic metals, and improving our understanding of bioremediation of metals.