Electrostatically-driven second sphere ligand switch between high and low reorganization energy forms of native cytochrome c

ALVAREZ PAGGI, D.; CASTRO M.A.; TÓRTORA V.; CASTRO L.; RADI, R.; MURGIDA D.H.

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2013 vol. 135 p. 4389 - 4397

0002-7863

We have employed a combination of protein film voltammetry, time-resolved vibrational spectroelectrochemistry and molecular dynamics simulations to evaluate the electron transfer reorganization free energy (λ) of cytochrome c (Cyt) in electrostatic complexes that mimic some basic features of protein-protein interactions. The results reveal the existence of two native-like conformations of Cyt that present significantly different λ values. Conversion from the high to the low λ forms is triggered by electrostatic interactions, and involves the rupture of a weak H-bond between first (M80) and second sphere (Y67) ligands of the heme iron, as a distinctive feature of the conformational switch. The two flexible Ω loops operate as transducers of the electrostatic signal. This fine-tuning effect is abolished in the Y67F Cyt mutant, which presents a λ value similar to the WT protein in electrostatic complexes. We propose that interactions of Cyt with the natural redox partner proteins activate a similar mechanism to minimize the reorganization energy of inter-protein electron transfer.