Thermodynamics of Electron
Flow in the Bacterial Deca-heme
Cytochrome MtrF
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Abstract
Electron-transporting multi-heme cytochromes are essential
to the
metabolism of microbes that inhabit soils and carry out important
biogeochemical processes. Recently the first crystal structure of
a prototype bacterial deca-heme cytochrome (MtrF) has been resolved
and its electrochemistry characterized. However, the molecular details
of electron transport along heme chains in the cytochrome are difficult
to access via experiment due to the nearly identical chemical nature
of the heme cofactors. Here we employ large-scale molecular dynamics
simulations to compute the redox potentials of the 10 hemes of MtrF
in aqueous solution. We find that as a whole they fall within a range
of ∼0.3 V, in agreement with experiment. Individual redox potentials
give rise to a free energy profile for electron transport that is
approximately symmetric with respect to the center of the protein.
Our calculations indicate that there is no significant potential bias
along the orthogonal octa- and tetra-heme chains, suggesting that
under aqueous conditions MtrF is a nearly reversible two-dimensional
conductor