Thermal Fluctuations Determine the Electron‐Transfer Rates of Cytochrome c in Electrostatic and Covalent Complexes

Abstract

The heterogeneous electron-transfer (ET) reaction of cytochrome c (Cyt-c) electrostatically or covalently immobilized on electrodes coated with self-assembled monolayers (SAMs) of omega-functionalized alkanethiols is analyzed by surface-enhanced resonance Raman (SERR) spectroscopy and molecular dynamics (MD) simulations. Electrostatically bound Cyt-c on pure carboxyl-terminated and mixed carboxyl/hydroxyl-terminated SAMs reveals the same distance dependence of the rate constants, that is, electron tunneling at long distances and a regime controlled by the protein orientational distribution and dynamics that leads to a nearly distance-independent rate constant at short distances. Qualitatively, the same behavior is found for covalently bound Cyt-c, although the apparent ET rates in the plateau region are lower since protein mobility is restricted due to formation of amide bonds between the protein and the SAM. The experimental findings are consistent with the results of MD simulations indicating that thermal fluctuations of the protein and interfacial solvent molecules can effectively modulate the electron tunneling probability.

Electric-field effects on the interfacial electron transfer and protein dynamics of cytochrome c

“…Thus, the kinetic analysis cannot be restricted to the redox process of the native state but must also include the formation of the B2 species. A qualitatively similar kinetic behaviour has been recently observed for Cyt-c covalently attached to SAM-coated Ag electrodes, and found to be adequately described by the scheme in which B1 ox exhibits a reaction channel to B2 ox [5cHS] in equilibrium with B2 ox [6cLS] [47]. In a similar way, we have considered the temporal evolution of the B2 species in the present kinetic analysis which thus allowed determining the relaxation constant k relax of the redox process of B1 (Table 1).…”

“…However, also small-amplitude fluctuations of water molecules in the Cyt-c/ SAM contact region are affected as concluded from recent studies on covalently attached Cyt-c that as well reveals a viscosity effect of k relax in the non-tunnelling regime [47].…”

“…The results obtained so far indicate that the overall redox process is determined by the coupling of protein dynamics with electron tunnelling [42,[46][47][48]. This coupling results from the fact that the energetically preferred electrostatic binding domain corresponds to an orientation of the bound protein that exhibits a distinctly lower tunnelling probability than a lower affinity binding site [46,48].…”

Kinetics, subcellular localization, and contribution to parasite virulence of a Trypanosoma cruzi hybrid type A heme peroxidase ( Tc APx-CcP)

“…The probability of ET toward the ferryl-oxoheme group was calculated using the pathways algorithm (56,57). This method looks for the best possible path connecting the electron donor and the acceptor, and it was successfully used by our group previously (58)(59)(60)(61)(62). Briefly, according to the Marcus theory (63), the ET rate constant (k ET ) depends on the reaction standard free energy (ΔG°), the reorganization energy (λ), and the electronic coupling matrix (T DA ), described in the following equation:…”

Structural and Molecular Basis of the Peroxynitrite-mediated Nitration and Inactivation of Trypanosoma cruzi Iron-Superoxide Dismutases (Fe-SODs) A and B

“…The method has been used successfully in previous work from our group (44,51,53). Pathways were computed between Cys 83 -S Ϫ and Tyr 35 -O ⅐ atoms located orbitals for 100 snapshots taken from the corresponding MD simulation.…”