Complex Formation with the Activator RACo Affects the Corrinoid Structure of CoFeSP

Activation of the corrinoid [Fe-S] protein (CoFeSP), involved in reductive CO₂ conversion, requires the reduction of the Co­(II) center by the [Fe-S] protein RACo, which according to the reduction potentials of the two proteins would correspond to an uphill electron transfer. In our resonance Raman spectroscopic work, we demonstrate that, as a conformational gate for the corrinoid reduction, complex formation of Co­(II)­FeSP and RACo specifically alters the structure of the corrinoid cofactor by modifying the interactions of the Co­(II) center with the axial ligand. On the basis of various deletion mutants, the potential interaction domains on the partner proteins can be predicted

Disentangling Electron Tunneling and Protein Dynamics of Cytochrome <i>c</i> through a Rationally Designed Surface Mutation

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 <i>c</i> 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