Electron transfer from cytochrome c to cupredoxins

Abstract

Electron transfer (ET) through and between proteins is a fundamental biological process. The activation energy for an ET reaction depends upon the Gibbs energy change upon ET (DeltaG(0)) and the reorganization energy. Here, we characterized ET from Pseudomonas aeruginosa cytochrome c(551) (PA) and its designed mutants to cupredoxins, Silene pratensis plastocyanin (PC) and Acidithiobacillus ferrooxidans rusticyanin (RC), through measurement of pseudo-first-order ET rate constants (k(obs)). The influence of the DeltaG (0) value for ET from PA to PC or RC on the k(obs) value was examined using a series of designed PA proteins exhibiting a variety of E (m) values, which afford the DeltaG (0) variation range of 58-399 meV. The plots of the k(obs) values obtained against the DeltaG(0) values for both PA-PC and PA-RC redox pairs could be fitted well with a single Marcus equation. We have shown that the ET activity of cytochrome c can be controlled by tuning the E(m) value of the protein through the substitution of amino acid residues located in hydrophobic-core regions relatively far from the redox center. These findings provide novel insights into the molecular design of cytochrome c, which could be utilized for controlling its ET activity by means of protein engineering.

NMR and DFT Investigation of Heme Ruffling: Functional Implications for Cytochrome c

“…Indeed, the increase of the total electronic energy as a function of the heme ruffling OOP deformation is steeper for the Fe(II) state as compared to the Fe(III) state. This DFT-predicted decrease of the heme reduction potential in response to increased ruffling is in accord with the measured decrease of the Pa cyt c 551 reduction potential by about 100 mV in the more ruffled F7A variant relative to WT 20,21,88. The prediction also agrees with the correlation between the heme ruffling OOP deformation and the reduction potentials of the individual hemes in cyts c 3 89.…”

The Influence of Heme Ruffling on Spin Densities in Ferricytochromes c Probed by Heme Core 13C NMR

“…Pa F7A, Ht K22M, Ht M13V, and Ht M13V/K22M have been previously determined to have lower redox potentials relative to their respective WT proteins, and among the Ht series of mutants, potential decreases as ruffling increases. 45,77 The results here support a general trend between increased ruffling and decreased redox potential.…”

Investigations of heme distortion, low-frequency vibrational excitations, and electron transfer in cytochrome c

“…This factor will act to increase the semiclassical Marcus barrier, ΔG ‡ s = ðΔG 0 red + λ s Þ 2 =4λ s , assuming the photoreduction takes place in the "normal" region of electron transfer kinetics (42). Similarly, ΔG 0 red may increase (becoming less negative) to some degree upon heme ruffling, which is consistent with the cyt c 551 reduction potentials (19). Moreover, treatment of inelastic processes (41) that lead to excitation of the ruffling vibration during the reaction will also effectively increase ΔG ‡ s .…”

“…Consequently, the electron transfer rate to the ferric heme is expected to decrease as a function of the ruffling deformation (17). In addition, when ruffling is considered in isolation, it decreases the reduction potential of ferric cyt c (19)(20)(21)(22).…”