Vol 68, No 6 (2023)

Influenza A virus pandemics still remain a threat to global health. One class of antiviral drugs, namely, inhibitors of the specific viral enzyme neuraminidase, is predominantly used in the fight against these pandemics. These antivirals include zanamivir (Relenza™) and oseltamivir (Tamiflu™). The viral resistance to this class of compounds steadily increases. The M2 proton channel of influenza A virus is an alternative clinically proven target for antiviral therapy. However, many circulating virus strains bear amino acid mutations in the M2 protein, causing resistance to drugs of the adamantane series, M2 blockers, such as rimantadine and amantadine. Consequently, inhibitors targeting mutants of the M2 channel are urgently needed for public biosafety and health. This review is devoted to structural-functional interactions used in practice and mediated by the action of experimental drugs on the protein target, the transmembrane domain of the influenza virus M2 proton channel. An analysis of the experimental and model structural data available in open access is presented.

A highly effective producer strain Escherichia coli C3030/pET23d+-EcHGPRT, allowing production of recombinant hypoxanthine‒guanine phosphoribosyltransferase from E. coli (EcHGPRT) in a soluble form, has been created. A method for isolating and purifying the recombinant protein has been developed. The specific activity against the natural substrate and pyrazine-2-carboxamide derivatives has been determined. Crystals of the EcHGPRT complexes with 3-hydroxypyrazine-2-carboxamide (T-1105) and 6-fluoro-3-hydroxypyrazine-2-carboxamide (T-705), suitable for X-ray diffraction analysis, have been grown by capillary counter diffusion. X-ray diffraction sets with a resolution of up to 2.4 and 2.5 Å have been collected at the ESRF synchrotron (France, station ID23-1) at a temperature of 100 K. The crystals belong to the sp. gr. P3(1)21; the independent part of the cell contains two enzyme molecules.

Coronavirus SARS-CoV-2 was the cause of global pandemic COVID-19 that has claimed millions of lives around the world. One of the approaches to the therapy of severe forms of COVID-19 is based on the use of virus-neutralizing antibodies against the receptor-binding domain (RBD) of the virus spike glycoprotein (S). Detailed structural data on particular epitopes recognized by these virus-neutralizing antibodies is an important aspect of the improvement of available antibodies in order to extend the range of recognized virus strains. A stoichiometric complex of the virus-neutralizing single-domain antibody P2C5 and the glycosylated form of SARS-CoV-2 S protein RBD was obtained. Despite numerous conditions in which the crystal growth of the complex was observed, these crystals showed poor diffraction, apparently because of heterogeneity associated with the glycosylation of RBD. With the aim of improving the crystal quality, deglycosylase PNGase F was produced in a bacterial expression system and deglycosylation of RBD was performed. Despite low solubility of the deglycosylated form of RBD, it retains the ability to bind to the nanoantibody P2C5, resulting in the formation of a stable heterodimeric complex during gel filtration. The crystals of this complex were obtained. They showed diffraction to a similar resolution of ~4 Å on a laboratory X-ray diffractometer and at a synchrotron radiation source. The symmetry space group, the unit cell parameters of the crystal, and its protein composition were determined.

The primary processes of photosynthesis for purple photosynthesising bacteria occur in light-harvesting (LH) complexes. The LH2 complex contains polypeptides; bacteriochlorophyll; and, in most cases, carotenoids. There are three known spatial structures of LH2 complexes from purple nonsulfur bacteria; however, high-resolution structures have not been established for purple sulfur bacteria. The results of the structural study of two light-harvesting complexes LH2 from purple sulfur bacteria Ectothiorhodospira haloalkaliphila by cryoelectronic microscopy are reported. Images of carotenoid-containing (LH2+) and carotenoidless (LH2–) variants of the complex, demonstrating a characteristic architecture of the objects of this type, are obtained. A 3D reconstruction of LH2+ is performed with a resolution of 4.5 Å; it coincides with the previously established crystal structure. The presence of particles of different morphology is shown for LH2–.

Previous studies of the spatial structure of the guest–host complexes of macrocyclic cavitands cucurbiturils with a number of nitroxyl radicals by ESR, NMR, and crystallographic methods showed that, in aqueous solutions containing a number of nitroxyl radicals as guest molecules, ordered aggregates in the form of an equilateral triangle, with three guest–host monocomplexes located in its vertices, may arise. We performed experiments on small-angle X-ray scattering of aqueous solutions of guest–host cucurbit[8]uril complexes with a stable nitroxyl radical (protonated tempoamine) and, based on the experimental results, carried out ab initio modeling of the shape of aggregates of complexes in the natural state in solution. The search for models of the shape of aggregates was performed either using no additional information about their structure or assuming the presence of a threefold axis. ESR is applied as an independent method for studying the aggregation of complexes in solution. It is shown that the shape of the particles constituting complexes at high cavitand and guest concentrations in an aqueous solution is close in its parameters to an equilateral triangle, which is in agreement with the known crystallographic and ESR data.

The structure of the Hfq protein from the bacterium Chromobacterium haemolyticum, which forms crystals in two different spatial groups, has been determined. In both cases, the protein has a specific quaternary hexamer-ring structure. The obtained structure showed a previously undescribed interaction between the C-terminal unstructured part of Hfq and the amino acid residues of the proximal RNA-binding site of the protein. This contact may contribute to the regulation of the binding of RNA molecules to the Hfq protein.

Crystals of the enzyme purine nucleoside phosphorylase from the extremophilic bacterium Halomonas Chromatireducens AGD 8-3, suitable for X-ray diffraction, were grown by the vapor-diffusion method. The X-ray diffraction data were collected from these crystals at the Belok beamline of the Kurchatov synchrotron radiation source (National Research Centre “Kurchatov Institute”) at 100 K to 1.80 Å resolution. The X-ray diffraction data were processed in the space groups P1, P2, P21, and P622. The structure was solved by the molecular replacement method taking into account the twinning in the space groups P21 and P1 with one and two hexamers of the enzyme per asymmetric unit, respectively.

D-cycloserine inhibits pyridoxal 5'-phosphate (PLP)-dependent enzymes both reversibly and irreversibly. As an alanine racemase inhibitor, D-cycloserine is used in drug therapy in the treatment of tuberculosis. Several products of the interaction of D-cycloserine and PLP in the active site of the enzyme are known. The crystal structure of the complex of PLP-dependent D-amino acid transaminase from the bacteria Aminobacterium colombiense (Amico) with D-cycloserine obtained at a resolution of 1.9 Å is presented, in which the ring-opened adduct of PLP and D-cycloserine was discovered. In addition, the interaction of D-cycloserine with Amico has been characterized by the kinetic and spectral methods, various products of the interaction of D-cycloserine and PLP in the active site of transaminase have been determined, and the coordination of D-cycloserine and PLP adducts in the Amico active site has been analyzed. It is established that the products of the interaction of D-cycloserine with PLP in the Amico active site are several compounds, including PLP and DCS adducts in the cyclic and open forms, oxime formed by PMP and β-aminooxy-D-alanine, and PMP and β-aminooxypyruvate.

The modified “simulated annealing” algorithm implemented in the DAMMINV software allows one to obtain 10 to 15 different nanoparticle models fitting small-angle X-ray scattering data. This method is based on the mode of intermittent weights of the objective function, which balances between minimization of the penalty coefficients, responsible for the model meaningfulness, and the discrepancy between the experimental and model scattering data. The effect of noise on the scattering curves on the quality of three-dimensional helix shape reconstruction has been investigated, and the results are compared with the data obtained using standard programs. The method has been verified on noise-free model data and data with superimposed Poisson noise by the example of a helix particle with a thickness of turns comparable to the characteristic size of the space between them. A comparative analysis of the reconstructed models and the three-dimensional shapes obtained using standard modes of the “simulated annealing” algorithm has been performed.

The behavior of a dimer isolated from the crystal structure of tetragonal lysozyme has been simulated using the accelerated molecular dynamics method. The simulation time was 240 ns. The simulation data are compared with the data obtained previously using classical molecular dynamics. It is shown that the dimer studied is stable in both experiments, but the accelerated molecular dynamics method made it possible to reveal additional conformational changes in lysozyme molecules.

The current epidemiological situation, including the existence of new SARS-CoV-2 virus with a high mutagenicity, requires fundamentally new deadlines for the development of vaccines, which may be achieved only applying modern computing technologies and simulation. Epitopes have been found in the spike protein of the SARS-CoV-2 virus using immunoinformatics methods, and their allergenicity and immunogenecity was predicted. It is shown that a vaccine against SARS-CoV-2 can be designed based on these epitopes.

Проанализирован геном африканской чумы свиней и выявлен белок, способный служить иммуногеном. Для водорастворимого фрагмента данного белка методом молекулярной динамики показано, что он стабилен в водно-солевом растворе. Иммуномоделирование показало, что данный фрагмент вызывает клеточный ответ, следовательно, может быть использован в качестве прототипа вакцины.

The molecular mechanisms of the interaction of anticancer antibiotic doxorubicin with lipid cell membrane models have been investigated using grazing incidence X-ray diffraction (XRD) and X-ray reflectivity (XRR). The model systems were monolayers of four types of phospholipids, related to the main components of animal cell membranes. New information on the processes of damage of phospholipid monolayer lattice caused by doxorubicin is obtained. It is established that the action of doxorubicin on anionic phospholipid monolayers is determined by the electrostatic interaction: positively charged doxorubicin molecules are incorporated between negatively charged phospholipid functional groups. In the case of neutral phospholipids the key role belongs to the hydrophobic interaction: doxorubicin molecules are coordinated with phospholipid hydrocarbon tails in disordered regions.

The calcium-carbonate-induced mineralization of multilayer shells of emulsion capsules, formed using layer-by-layer assembly of polyelectrolytes, has been investigated. Optimal conditions for forming microcapsules with a core from shea butter and an organic–inorganic shell from synthetic polyelectrolytes and calcium carbonate are found. The shell morphology and stability of capsules in an aqueous suspension upon heating are investigated, and their cytotoxicity for human fibroblast cells is estimated. It is shown that mineralization of emulsion polyelectrolyte capsules by calcium carbonate in the form of vaterite strengthens the capsule walls and increases their biocompatibility.