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Disentangling Electron Tunneling and Protein Dynamics of Cytochrome c through a Rationally Designed Surface Mutation
Citation key Alvarez-Paggi2013
Author Alvarez-Paggi, Damian and Meister, Wiebke and Kuhlmann, Uwe and Weidinger, Inez and Tenger, Katalin and Zimanyi, Laszlo and Rakhely, Gabor and Hildebrandt, Peter and Murgida, Daniel H.
Pages 6061–6068
Year 2013
DOI 10.1021/jp400832m
Journal Journal of Physical Chemistry B
Volume 117
Number 20
Abstract Nonexponential distance dependence of the apparent electron-transfer (ET) rate has been reported for a variety of redox proteins immobilized on biocompatible electrodes, thus posing a physicochemical challenge of possible physiological relevance. We have recently proposed that this behavior may arise not only from the structural and dynamical complexity of the redox proteins but also from their interplay with strong electric fields present in the experimental setups and in vivo (J. Am Chem. Soc. 2010, 132, 5769-5778). Therefore, protein dynamics are finely controlled by the energetics of both specific contacts and the interaction between the protein's dipole moment and the interfacial electric fields. In turn, protein dynamics may govern electron-transfer kinetics through reorientation from low to high donor acceptor electronic coupling orientations. Here we present a combined computational and experimental study of WT cytochrome c and the surface mutant K87C adsorbed on electrodes coated with self-assembled monolayers (SAMs) of varying thickness (i.e., variable strength of the interfacial electric field). Replacement of the positively charged K87 by a neutral amino acid allowed us to disentangle protein dynamics and electron tunneling from the reaction kinetics and to rationalize the anomalous distance dependence in terms of (at least) two populations of distinct average electronic couplings. Thus, it was possible to recover the exponential distance dependence expected from ET theory. These results pave the way for gaining further insight into the parameters that control protein electron transfer.
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