Surface-enhanced vibrational spectroscopy for probing transient interactions of proteins with biomimetic interfaces: electric field effects on structure, dynamics and function of cytochrome c.

Most of the biochemical and biophysical processes of proteins take place at membranes, and are 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, biomimetic interfaces may be employed that consist of membrane models deposited on nanostructured metal electrodes. For such devices, surface-enhanced resonance Raman and IR absorption spectroscopy are powerful techniques to disentangle the complex interfacial processes of proteins in terms of rotational diffusion, electron transfer, and protein and cofactor structural changes. The present article reviews the results obtained for the haem protein cytochrome c, which is widely used as a model protein for studying the various reaction steps of interfacial redox processes in general. In addition, it is shown that electric field effects may be functional for the natural redox processes of cytochrome c in the respiratory chain, as well as for the switch from the redox to the peroxidase function, one of the key events preceding apoptosis.