Luciano A. Abriata Damián Álvarez-Paggi Gabriela N. Ledesma Ninian J. Blackburn Alejandro J. Vila and Daniel H. Murgida. Alternative ground states enable pathway switching in biological electron transfer. PNAS 2012 109(43): 17348-17353.
Abstract
Electron transfer is the simplest chemical reaction and constitutes the basis of a large variety of biological processes such as photosynthesis and cellular respiration. Nature has evolved specific proteins and cofactors for these functions. The mechanisms optimizing biological electron transfer have been matter of intense debate such as the role of the protein milieu between donor and acceptor sites. Here we propose a mechanism regulating long-range electron transfer in proteins. Specifically we report a spectroscopic electrochemical and theoretical study on WT and single-mutant CuA redox centers from Thermus thermophilus which shows that thermal fluctuations may populate two alternative ground-state electronic wave functions optimized for electron entry and exit respectively through two different and nearly perpendicular pathways. These findings suggest a unique role for alternative or “invisible” electronic ground states in directional electron transfer. Moreover it is shown that this energy gap and therefore the equilibrium between ground states can be fine-tuned by minor perturbations suggesting alternative ways through which protein–protein interactions and membrane potential may optimize and regulate electron–proton energy transduction.
