Vol 88, No 5 (2023)

The review analyzes modern concepts regarding the control of various mechanisms of the hippocampal neuroplasticity in adult mammals and humans by glucocorticoids. Glucocorticoid hormones ensure the coordinated functioning of key components and mechanisms of hippocampal plasticity: neurogenesis, glutamatergic neurotransmission, microglia and astrocytes, systems of neurotrophic factors, neuroinflammation, protease activities, metabolic hormones, neurosteroids. Regulatory mechanisms are diverse; along with the direct action of glucocorticoids through their receptors, there are indirect glucocorticoid-dependent effects, as well as numerous interactions between various systems and components. Despite the fact that many connections in this complex regulatory scheme have not yet been established, the study of the factors and mechanisms considered in the review forms growth points in the field of glucocorticoid-regulated processes in the brain and primarily in the hippocampus. These studies are fundamentally important for the translation into the clinic and the potential treatment/prevention of common diseases of the emotional and cognitive spheres and respective comorbid conditions.

O-acetylhomoserine sulfhydrylase is one of the key enzymes in the biosynthesis of methionine in Clostridioides difficile. The mechanism of the γ-substitution reaction of O-acetyl-L-homoserine catalyzed by this enzyme is the least studied among pyridoxal-5′-phosphate-dependent enzymes involved in the metabolism of cysteine and methionine. To clarify the role of the active site residues Tyr52 and Tyr107, four mutant forms of the enzyme with replacements for phenylalanine and alanine were obtained. The catalytic and spectral properties of mutant forms were investigated. The rate of the γ-substitution reaction catalyzed by mutant forms with the replacement of the Tyr52 residue decreased by more than three orders of magnitude compared to the wild-type enzyme. Tyr107Phe and Tyr107Ala mutant forms practically did not catalyze this reaction. Replacements of the residues Tyr52 and Tyr107 led to a decrease in the affinity of the apoenzyme to the coenzyme by three orders of magnitude and changes in the ionic state of the internal aldimine of the enzyme. The obtained results allowed us to assume that Tyr52 is involved in ensuring the optimal position of the catalytic coenzyme-binding lysine residue at the stages of C-α-proton elimination and elimination of the side group of the substrate. Tyr107 can act as a general acid catalyst at the stage of acetate elimination.

Oxylipins are signal lipids derived from polyunsaturated fatty acids (PUFAs), which are formed by polyenzymatic multi-acid pathways of danger (cyclooxygenase, lipoxygenase, epoxygenase, anandamide), as well as non-enzymatically. These PUFA transformation pathways are activated in parallel, forming a mixture of active inclusions. Although the combination of oxylipins with tumor secretions was performed a long time ago, the methods of instrumental analysis have only recently been improved, measurements of oxylipins of different classes (profiles) have been compared. The review considers approaches to obtaining the profile of oxylipins by HPLC-MS/MS. The profiles of oxylipins in samples of patients with oncological diseases (breast cancer, colorectal cancer, ovarian cancer, lung cancer, prostate cancer, liver cancer) were compared. The conclusion is made about the possible possibilities of using the profile of blood oxylipins as markers of oncological diseases. Understanding the high level of exceeding the level of PUFAs and the physiological activity of oxylipin mixtures will be accompanied by the perfection of early diagnosis and prediction of the course of tumor diseases.

The structure and function of the bacterial nucleoid is controlled by nucleoid-associated NAP proteins. In any phase of growth, various NAPs, acting sequentially, condense the nucleoid and provide its transcriptionally active structure. However, in the late stationary phase, only one of the NAPs, the Dps protein, is strongly expressed, and DNA-protein crystals are formed that transform the nucleoid into a static, transcriptionally inactive structure, effectively protected from external influences. The discovery of crystal structures in living cells and the association of this phenomenon with bacterial resistance to antibiotics has aroused great interest in studying this phenomenon. The aim of this work is to obtain and compare the structures of two related NAPs (HU and IHF), since they are the ones that accumulate in the cell at the late stationary stage of growth, which precedes the formation of the protective DNA-Dps crystalline complex. For structural studies, two complementary methods were used in the work: small-angle X-ray scattering (SAXS) as the main method for studying the structure of proteins in solution and dynamic light scattering as an additional one. Various approaches and computer programs were used to interpret the SAXS data, which made it possible to determine the macromolecular characteristics and obtain reliable structural 3D models of various oligomeric forms of the HU and IHF proteins. It was shown that these proteins oligomerize in solution to varying degrees, and IHF is characterized by the presence of large oligomers consisting of initial dimers arranged in a chain. It was suggested that just before Dps expression, it is this protein that forms the toroidal structures previously observed in vivo and prepares the platform for the formation of DNA-Dps crystals. The results obtained are necessary for further study of the phenomenon of biocrystal formation in bacterial cells and finding ways to overcome the resistance of various pathogens to external conditions.

Glutaredoxin (Grx) is an antioxidant redox protein that uses glutathione (GSH) as an electron donor. Grx plays a crucial role in various cellular processes, such as antioxidant defense, control of cellular redox state, redox control of transcription, reversible S-glutathionylation of specific proteins, apoptosis, cell differentiation, etc. In the current study, we have isolated and characterized dithiol glutaredoxin from Hydra vulgaris Ind-Pune (HvGrx1). Sequence analysis showed that HvGrx1 belongs to the Grx family with the classical Grx motif (CPYC). Phylogenetic analysis and homology modeling revealed that HvGrx1 is closely related to Grx2 from zebrafish. HvGrx1 gene was cloned and expressed in Escherichia coli cells; the purified protein had a molecular weight of 11.82 kDa. HvGrx1 efficiently reduced β-hydroxyethyl disulfide (HED) with the temperature optimum of 25°C and pH optimum 8.0. HvGrx1 was ubiquitously expressed in all body parts of Hydra. Expression of HvGrx1 mRNA and enzymatic activity of HvGrx1 were significantly upregulated post H₂O₂ treatment. When expressed in human cells, HvGrx1 protected the cells from oxidative stress and enhanced cell proliferation and migration. Although Hydra is a simple invertebrate, HvGrx1 is evolutionary closer to its homologs from higher vertebrates (similar to many other Hydra proteins).

D-cycloserine inhibits pyridoxal-5′-phosphate (PLP)-dependent enzymes. The inhibition efficiency depends on the organization of their active center and the mechanism of the catalyzed reaction. D-cycloserine interacts with the PLP form of enzyme similarly to substrate amino donor, and the interaction is predominantly reversible. Inhibition products include hydroxyisoxazole-pyridoxamine-5′-phosphate, oxime between PLP and β-aminooxy-D-alanine, ketimine between pyridoxamine-5′-phosphate and cyclic or open forms of D-cycloserine, pyridoxamine-5′-phosphate, etc. For some enzymes the formation of a stable aromatic product - hydroxyisoxazole can lead to irreversible D-cycloserine inhibition at certain pH value. The aim of this work was to study the mechanism of D-cycloserine inhibition of PLP-dependent D-amino acid transaminase from the bacterium Haliscomenobacter hydrossis. Spectral methods revealed several products of the interaction of D-cycloserine with PLP in the active site of transaminase: oxime between PLP and β-aminooxy-D-alanine, ketimine between pyridoxamine-5′-phosphate and cyclic or open forms of D-cycloserine, pyridoxamine-5′-phosphate. The formation of hydroxyisoxazole-pyridoxamine-5′-phosphate was not observed. The 3D structure of the complex of transaminase with D-cycloserine was obtained by X-ray diffraction analysis. In the active site of transaminase, a ketimine adduct between pyridoxamine-5′-phosphate and D-cycloserine in the cyclic form was found; the ketimine occupied two positions and was coordinated via hydrogen bonds with different active site residues. Using kinetic and spectral methods we have shown that D-cycloserine inhibition is reversible, and the activity of transaminase from H. hydrossis can be restored by adding an excess of keto substrate as well as by adding an excess of cofactor. The results obtained confirm the reversibility of D-cycloserine inhibition and the conversion of various adducts of D-cycloserine and PLP into each other.

In the green bacteria Chloroflexus (Cfx.) aurantiacus, the process of photosynthesis begins with the absorption of light by chlorosomes, peripheral antennas consisting of thousands of bacteriochlorophyll c (BChl c) molecules combined into oligomeric structures. In this case, excited states are formed in BChl c, the energy of which migrates along the chlorosome towards the baseplate and further to the reaction center, where the primary charge separation occurs. Energy migration is accompanied by nonradiative electronic transitions between numerous exciton states, that is exciton relaxation. In this work, we studied the dynamics of exciton relaxation in Cfx. aurantiacus chlorosomes using difference femtosecond spectroscopy at cryogenic temperature (80 K). Chlorosomes were excited by 20 fs light pulses at wavelengths from 660 to 750 nm, and the difference (light-dark) kinetics were measured at a wavelength of 755 nm. Mathematical analysis of the data obtained revealed the kinetic components with characteristic time constants of 140, 220, and 320 fs responsible for the exciton relaxation. As the excitation wavelength decreased, the number of components and their relative contribution increased. Theoretical modeling of the results obtained was carried out on the base of the cylindrical model of BChl c aggregates. Nonradiative transitions between groups of exciton bands were ascribed by the system of kinetic equations. The model in which the energetic and structural disorder was taken into account turned out to be the most adequate.