Membrane Potential Control of Electron Shuttle and Peroxidase Activity of Heme Proteins in Biomimetic Systems

MURGIDA, D. H.

Salta

Congreso; 3rd Latin American Protein Society Meeting; 2010

Electron transfer (ET) chains involved in photosynthesis and aerobic respiration take place at the level of biological membranes where protein complexes exert their function under the influence of strong electric fields. Here we report a study on the influence of these fields on the structure and ET dynamics of different 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. The proteins are immobilized on nanostructured Ag electrodes coated with biomimetic films that are designed depending on the surface properties of each redox protein.1,2 Structure, ET kinetics and protein dynamics are studied simultaneously by using two-colors time-resolved surface-enhanced resonance Raman (TR-SERR) spectroelectrochemistry.2 The atomistic interpretation of the experiments is guided by molecular dynamics (MD) simulations and electron pathways calculations of the biomimetic complexes. This powerful combination of theoretical and experimental methods provides a detailed and consistent picture of the interfacial ET mechanisms.3 In each case it is concluded that the overall ET rates are determined by an interplay of protein dynamics and tunneling probabilities at the different conformations along the dynamics. In turn, protein dynamics is strongly modulated by the interfacial electric field, as demonstrated by TR-SERR experiments and MD simulations performed under different conditions. It is also shown that sufficiently strong electric fields are able to induce reversible and irreversible structural changes of the ferric proteins in the complexes, which produce a dramatic down-shift of the reduction potentials ann  gain of peroxidase function pesumably involved in the early steps of apoptosis. For the natural partner protein of most cytochromes, i.e. the CuA center of cyt-c oxidase, local and global electrostatics are also shown to be crucial in modulating reduction potentials, reorganization energies and crucial structural features. Based on these results it is hypothesized that transmembrane potentials play a regulatory role in respiration and photosynthesis via a feedback inhibition mechanism.