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Bound Flavin-Cytochrome Model of Extracellular Electron Transfer in Shewanella oneidensis: Analysis by Free Energy Molecular (Postprint)
AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH WRIGHT-PATTERSON AFB United States
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Flavins are known to enhance extracellular electron transfer EET in Shewanella oneidensis MR-1 bacteria, which reduce electron acceptors through outer-membrane OM cytochromes c. Free-shuttle and bound-redox cofactor mechanisms were proposed to explain this enhancement, but recent electrochemical reports favor a flavin-bound model, proposing two one-electron reductions of flavin, namely, oxidized Ox to semiquinone Sq and semiquinone to hydroquinone Hq, at anodic and cathodic conditions, respectively. In this work, to provide a mechanistic understanding of riboflavin RF binding at the multiheme OM cytochrome OmcA, we explored binding configurations at hemes 2, 5, 7, and 10. Subsequently, on the basis of molecular dynamics MD simulations, binding free energies and redox potential shifts upon RF binding for the OxSq and SqHq reductions were analyzed. Our results demonstrated an upshift in the OxSq and a downshift in the SqHq redox potentials, consistent with a bound RFOmcA model. Furthermore, binding free energy MD simulations indicated an RF binding preference at heme 7.
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