Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 106, Issue 52, Pages 22169-22174Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0900086106
Keywords
cytochrome-c; iron respiration; protein film voltammetry; electron paramagnetic resonance; Shewanella
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Funding
- Department of Energy's Office of Biological and Environmental Research, at Pacific Northwest National Laboratory (PNNL)
- National Science Foundation [EAR 05-19144]
- Center for Environmental Kinetics Analysis (NSF) [CHE-0431328]
- U.S. Department of Energy, Biological and Environmental Research
- Royal Society Wolfson Foundation
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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 beta-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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