ИСТИНА

The rate of electron transfer (ET) in membrane proteins depends on the distance between redox-cofactors, free energy difference and activation energy of ET reactions. All these factors may be affected by conformational mobility of the protein. Photosystem I (PS I) is an excellent model for the study of the effect of conformational mobility on the ET reactions for several reasons: 1) the availability of 3D-structure at 2.5 Å resolution, 2) the variety of site-directed mutants, 3) the possibility to monitor the single flash-induced kinetics of ET reactions in the wide time range. The effects of conformational mobility on the ET in PS I were studied mostly at cryogenic temperatures in water-glycerol mixtures [1, 2]. An alternative approach is the alteration of protein functioning in dry trehalose glassy matrices at room temperature [3, 4]. A number of similarities are apparent in the charge recombination kinetics of PS I immobilized in the frozen glycerol at 170 K and in the trehalose glass at 298 K. At high temperature/humidity, recombination occurs predominantly from the terminal iron-sulfur clusters FA/FB, but on transition to the glassy state, its contribution decreases at the expense of an increase in the recombination from both cluster FX − and phylloquinone A1 −. The backward ET from the FX in both cases is significantly heterogeneous, covering the wide time range from 0.5 ms to 30 ms. The distinctions between two glass states include different amplitudes of recombination from FX − and A1 − and different kinetics of recombination from A1 −. We propose that desiccation of trehalose matrix at room temperature and freezing of the water-glycerol solution below its glass transition point cause similar changes in the protein, altering apparent activation energy. In case of trehalose matrix, these changes are more pronounced in peripheral regions of PS I, while at low temperature this effect is evenly spread through the whole protein. This work was supported by the Russian Foundation for Basic Research (17-00-00201). References 1. E. Schlodder et al (1998) Biochemistry, 37, pp. 9466–9476. 2. D. Cherepanov et al (2018) J. Phys. Chem. B 122, pp. 7943–7955. 3. M. Malferrari et al (2016) Biochim. Biophys. Acta 1857, pp. 1440–1454. 4. V. Kurashov et al (2018) Biochim. Biophys. Acta 1859, pp. 1288–1301.