The first steps of the global process of photosynthesis take place in specialized membrane pigment–protein complexes called photosynthetic reaction centers (RCs). The RC of the photosynthetic purple bacterium Rhodobacter sphaeroides, a relatively simple analog of the more complexly organized photosystem II in plants, algae and cyanobacteria, serves as a convenient model for studying pigment–protein interactions that affect photochemical processes. In bacterial RCs the bacteriochlorophyll (BChl) dimer P serves as the primary electron donor, and its redox potential is a critical factor in the efficient functioning of the RC. It has previously been shown that the replacement of Phe M197 by His strongly affects the oxidation potential of P (E _m P/P⁺), increasing its value by 125 mV, as well as increasing the thermal stability of RC and its stability in response to external pressure. The crystal structures of F(M197)H RC at high resolution obtained using various techniques presented in this report clarify the optical and electrochemical properties of the primary electron donor and the increased resistance of the mutant complex to denaturation. The electron-density maps are consistent with the donation of a hydrogen bond from the imidazole group of His M197 to the C2-acetyl carbonyl group of BChl P_B. The formation of this hydrogen bond leads to a considerable out-of-plane rotation of the acetyl carbonyl group and results in a 1.2 Å shift of the O atom of this group relative to the wild-type structure. Besides, the distance between BChl P_A and P_B in the area of pyrrole ring I was found to be increased by up to 0.17 Å. These structural changes are discussed in association with the spectral properties of BChl dimer P. The electron-density maps strongly suggest that the imidazole group of His M197 accepts another hydrogen bond from the nearest water molecule, which in turn appears to form two more hydrogen bonds to Asn M195 and Asp L155. As a result of the F(M197)H mutation, BChl P_B finds itself connected to the extensive hydrogen-bonding network that pre-existed in wild-type RC. Dissimilarities in the two hydrogen-bonding networks near the M197 and L168 sites may account for the different changes of the E _m P/P⁺ in F(M197)H and H(L168)F RCs. The involvement of His M197 in the hydrogen-bonding network also appears to be related to stabilization of the F(M197)H RC structure. Analysis of the experimental data presented here and of the data available in the literature points to the fact that the hydrogen-bonding networks in the vicinity of BChl dimer P may play an important role in fine-tuning the redox properties of the primary electron donor.

With the recent developments in the field of free-electron-laser-based serial femtosecond crystallography, the necessity to obtain a large number of high-quality crystals has emerged. In this work crystallization techniques were selected, tested and optimized for the lipid mesophase crystallization of the Rhodobacter sphaeroides membrane pigment-protein complex, known as the photosynthetic reaction center (RC). Novel approaches for lipid sponge phase crystallization in comparatively large volumes using Hamilton gas-tight glass syringes and plastic pipetting tips are described. An analysis of RC crystal structures obtained by lipid mesophase crystallization revealed non-native ligands that displaced the native electron-transfer cofactors (carotenoid spheroidene and a ubiquinone molecule) from their binding pockets. These ligands were identified and were found to be lipids that are major mesophase components. The selection of distinct co-crystallization conditions with the missing cofactors facilitated the restoration of spheroidene in its binding site.

Introduction.The trend of teaching staff aging in secondary schools is evident in many countries. A negative consequence of this is the growing gap between the personal resources of teachers and the requirements of the profession. Solving the problem of maintaining an optimal age structure involves studying its dynamics and forecasting its development in order to develop measures for personnel planning. The present paper presents the results of the analysis of the current age structure of teachers in the regional context (in the subjects of the Russian Federation) and develops a forecast for its development.The aimof the current research was to present the results of the development of a medium-term (until 2024) forecast of the age structure of teachers in the subjects of the Russian Federation.Methodology and research methods.The research was based on a general scientific methodology applying a systematic approach and the methods of statistical analysis, comparison, generalisation, systematisation, structuring, interpretation, extrapolation, forecasting, and graphical representation of data. The authors analysed the data in official statistics of the Russian Federation and the Organisation for Economic Cooperation and Development. The provisions of normative and legislative documents in the field of strategic regulation of education in the Russian Federation, scientific publications of Russian and foreign researchers in the Scopus, Web of Science, and Science Index databases were investigated as well.Results.The authors identify and highlight the factors, which have the most significant impact on the current state of personnel support for educational activities in the world. The analysis of age-specific teacher characteristics in cross-country comparison is performed. The assessment of age structure of general education teaching personnel in Russia as a whole and at the regional level is carried out. The forecast for its development for the period up to 2024 is developed. Scientific novelty. The conceptual feature of the present study lies in the view of the trends in the development of age cohorts in homogeneous groups. The approach employed allows for increasing the accuracy of forecasting of teacher demand, taking into account the specifics of regional demand.Practical significance.Taking the specifics of the regions into consideration, it will be possible to improve the quality of education. The results of the research can be used by specialists in the course of conducting international research, planning teacher training, and developing measures to enhance the prestige of teaching profession and to stimulate the influx of young personnel to schools at the Federal level and in the regions of the Russian Federation.

This review focuses on recent experimental data obtained by site-directed mutagenesis of the reaction center in purple nonsulfur bacteria. The role of axial ligation of (bacterio)chlorophylls in the...

The photosynthetic reaction center of the purple nonsulfur bacterium Cereibacter sphaeroides is a useful model for the study of mechanisms of photoinduced electron transfer and a promising component for photo-bio-electrocatalytic systems. The basic research and technological applications of this membrane pigment-protein complex require effective approaches to increase its structural stability. In this work, a rational design approach to genetically modify the reaction centers by introducing disulfide bonds is used. This resulted in significantly increasing the thermal stability of some of the mutant pigment-protein complexes. The formation of the S-S bonds was confirmed by X-ray crystallography as well as SDS-PAGE, and the optical properties of the reaction centers were studied. The genetically modified reaction centers presented here preserved their ability for photochemical charge separation and could be of interest for basic science and biotechnology.

Histidine M182 in the reaction center (RC) of Rhodobacter sphaeroides serves as the fifth ligand of the bacterio-chlorophyll (BChl) BBMg atom. When this His is substituted by an amino acid that is...