Protein dynamics control of electron transfer in reaction centers from Rps. viridisстатья
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Дата последнего поиска статьи во внешних источниках: 24 октября 2018 г.
Аннотация:Electron transfer (ET) in the reaction center from Rhodopseudomonas viridis has been studied experimentally by our group in the range of temperatures of 153 - 295 K. The kinetics of ET reaction from the proximal heme of cytochrome to the special pair was found to be non-exponential. The degree of non-exponentiality strongly depends on temperature, with increasing non-exponentiality at lower temperatures. Here, the experimental kinetic data for ET are analyzed in the frames of a theoretical Sumi - Marcus-type model, which allows establishing a connection between the observed kinetics and local structural dynamics of the protein in a close vicinity of the donor and acceptor sites. The phenomenological model subdivides the multi-time-scale dynamics of the protein into two groups: fast and slow. The division is determined by the rate of ET, which is dynamically controlled by the slow modes of the protein medium. The slow modes are described by a phenomenological collective coordinate X, for which a diffusion type of dynamics is assumed. The analysis of the temperature dependence of the kinetic curves for ET allows a complete characterization of the slow time-scale protein dynamics: we find the corresponding activation barrier for the dynamics of X, around 0.5 eV and the exponential pre-factor, which is in the range of 10(-16) s. The pre-exponential factor is lower than is expected for a typical activation process described by the transition state theory. We discuss the nature of the collective modes X, the nature of its activation barrier ( breaking of hydrogen bonds) and possible explanations for a low-pre-exponential factor of its dynamics. The main conclusion of the paper is that the kinetics of ET at low-temperatures can be used as a probe of protein structural dynamics in the microsecond time-scale, the time-scale that is not easily accessible by the computer simulations methods and can be complementary to other experimental techniques.