Characterization of an electron conduit between bacteria and the extracellular environment |
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| Authors: | Robert S. Hartshorne Catherine L. Reardon Daniel Ross Jochen Nuester Thomas A. Clarke Andrew J. Gates Paul C. Mills Jim K. Fredrickson John M. Zachara Liang Shi Alex S. Beliaev Matthew J. Marshall Ming Tien Susan Brantley Julea N. Butt David J. Richardson |
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| Affiliation: | aSchool of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom; ;bPacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352; and ;Departments of cBiochemistry and Molecular Biology, and ;dGeoscience, Pennsylvania State University, University Park, PA 16802-4500 |
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| Abstract: | A number of species of Gram-negative bacteria can use insoluble minerals of Fe(III) and Mn(IV) as extracellular respiratory electron acceptors. In some species of Shewanella, deca-heme electron transfer proteins lie at the extracellular face of the outer membrane (OM), where they can interact with insoluble substrates. To reduce extracellular substrates, these redox proteins must be charged by the inner membrane/periplasmic electron transfer system. Here, we present a spectro-potentiometric characterization of a trans-OM icosa-heme complex, MtrCAB, and demonstrate its capacity to move electrons across a lipid bilayer after incorporation into proteoliposomes. We also show that a stable MtrAB subcomplex can assemble in the absence of MtrC; an MtrBC subcomplex is not assembled in the absence of MtrA; and MtrA is only associated to the membrane in cells when MtrB is present. We propose a model for the modular organization of the MtrCAB complex in which MtrC is an extracellular element that mediates electron transfer to extracellular substrates and MtrB is a trans-OM spanning β-barrel protein that serves as a sheath, within which MtrA and MtrC exchange electrons. We have identified the MtrAB module in a range of bacterial phyla, suggesting that it is widely used in electron exchange with the extracellular environment. |
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| Keywords: | cytochrome-c iron respiration protein film voltammetry electron paramagnetic resonance Shewanella |
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