Structural and Dynamic Determinants of Protein Electron Transfer

MURGIDA D. H.

Horco Molle, Tucumán

Workshop; DAAD Workshop on Protein Dynamics and Reactivity; 2011

Most of the biochemical and biophysical processes of redox proteins take place at membranes and thus under the influence of strong local electric fields which are likely to affect the structure as well as the reaction mechanism and dynamics. To analyse such electric field effects we have employed biomimetic interfaces for protein attachment that consist of membrane models deposited on nanostructured metal electrodes. For such devices, surface enhanced resonance Raman and infrared absorption spectroscopy are powerful techniques to disentangle the complex interfacial processes of proteins in terms of rotational diffusion, electron transfer, as well as protein and cofactor structural changes. The atomistic interpretation of the experiments is guided by molecular dynamics (MD) simulations and electron pathways calculations of the biomimetic complexes. Using this approach we have investigated a variety of heme soluble proteins (cyt-c; cyt-b562, cyt-c6, iso-cyt-c) that act as electron shuttles in photosynthetic and respiratory chains of different organisms, as well as membrane terminal respiratory enzymes. In general terms it is concluded that the overall ET rates are determined by the interplay of protein dynamics and tunnelling probabilities at the different conformations along the dynamics, which in turn is strongly modulated by the local electric field. It is also shown that sufficiently strong electric fields are able to induce reversible structural changes of the proteins, affecting thermodynamic and kinetic parameters of the ET reactions. Based on these results it is hypothesized that transmembrane potentials play a regulatory role in respiration and photosynthesis via a feedback inhibition mechanism. In addition, it is shown that electric field effects may be functional for the switch from the redox to the peroxidase function of cytochrome c, one of the key events in programmed cellular death.