Angela M. Barragan, Alexander V. Soudackov, Zaida Luthey-Schulten, Sharon
Hammes-Schiffer, Klaus Schulten, and Ilia A. Solov'yov.
Theoretical description of the primary proton-coupled electron
transfer reaction in the cytochrome bc1 complex.
Journal of the American Chemical Society, 143:715-723, 2021.
BARR2021-KS
The cytochrome bc1 complex is a transmembrane enzymatic protein
complex that plays a central role in cellular energy production and is
present in both photosynthetic and respiratory chain organelles. Its
reaction mechanism is initiated by the binding of a quinol molecule to
an active site, followed by a series of charge transfer reactions
between the quinol and protein subunits. Previous work hypothesized
that the primary reaction was a concerted proton-coupled electron
transfer (PCET) reaction because of the apparent absence of
intermediate states associated with single proton or electron transfer
reactions. In the present study, the kinetics of the primary bc1
complex PCET reaction is investigated with a vibronically nonadiabatic
PCET theory in conjunction with all-atom molecular dynamics
simulations and electronic structure calculations. The computed rate
constants and relatively high kinetic isotope effects are consistent
with experimental measurements on related biomimetic systems. The
analysis implicates a concerted PCET mechanism with significant
hydrogen tunneling and nonadiabatic effects in the bc1 complex.
Moreover, the employed theoretical framework is shown to serve as a
general strategy for describing PCET reactions in bioenergetic
systems.
