Direct Observation of Protein Dynamics at Biomimetic Electrochemical Interfaces

MURGIDA, D.H.

Sevilla

Congreso; 59th Annual Meeting of the International Society of Electrochemistry; 2008

Heterogeneous electron transfer of proteins at biomimetic interfaces is characterized by ?unusual? distance dependences of the electron transfer rates, whose origin has been elusive and controversial. Using a two colours time-resolved surface-enhanced resonance Raman spectroelectrochemical approach we have been able to monitor simultaneously and in real time the structure, electron transfer kinetics and configurational fluctuations of heme proteins immobilized on SAM-coated electrodes. It is shown that the overall electron transfer kinetics is determined by protein dynamics rather than by tunnelling probabilities. Protein dynamics, in turn, is controlled by the interfacial electric field. Molecular dynamics simulations and pathway calculations show that the distribution of protein orientations in electrostatic complexes with SAM-coated electrodes is redox state dependent. Each orientation corresponds to a finite coupling, but significant couplings are only observed for a very narrow range of orientations in each redox state. Deviations larger than five degrees from the optimal orientation of the heme with respect to the electrode surface result in a drastic decay of the electronic coupling. Thus, measured electron transfer rates are a convolution of the dynamic sampling of the surface by the protein and electron tunneling probabilities at each configuration. Implications for inter-protein electron transfer at biological membranes and for bioelectrochemistry in general will be duscussed.