Electron transfer (ET) across protein-protein interfaces is less well understood than ET within a single protein. Previous experiments indicated the importance of Trp191 as a hole hopping intermediate site in the cytochrome c peroxidase-cytochrome c (CcP/Cc) complex.  Indeed, the cytochrome c peroxidase enzymatic activities and corresponding charge recombination rates vary among the wild type and W191X (X = Y, F, and G) mutants, as well as W191G with four bound redox-active small molecules. We performed theoretical studies of the electron transfer mechanism in these mutants by estimating the key ET parameters, including electronic couplings, reorganization energies, and reaction free energies. The analysis constrains the location of the radical cation during charge recombination and the corresponding kinetics. For the W191F and W191G mutants, the electronic couplings are predicted to be orders of magnitude smaller than in the native protein. In W191Y, the redox potential difference between tyrosine and tryptophan influences the recombination rate by orders of magnitude. We also find an order of magnitude decrease in the electronic coupling for the W191G bound small molecule systems, due to the large donor-acceptor separation between the small molecules and the Cc heme. Taken together, our analysis indicates the important role of tryptophan as a hole hopping intermediate for charge recombination in the CcP/Cc complex, consistent with prior studies, and suggests tryptophan oxidation as the most effective accelerator in this prototype of long-range inter-protein ET.<br/>

Theoretical studies of cytochrome c peroxidase - cytochrome c electron transfer: The role of tryptophan

255th National Meeting (2018)

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