The interaction of DNA with Mn²⁺ was studied in absorbance and optical activity in the electronic and vibrational regions. Based on the data, several stages of the interaction were identified. Con formational transition towards the C‐form of DNA was observed in solution at the molar ratio Mn²⁺/DNA‐phosphates between 0.1 and 1.5. The exact ratio depended on the ionic strength and increased with increasing NaCl concentration. Although manganese interacted with the phosphates and bases of DNA at higher metal concentrations, it is unlikely that direct chelation occurred. A model for the interaction between manganese ions and DNA mediated by water is suggested destabilizing the double helix and partially breaking the hydrogen bonds between the base pairs. At high Mn²⁺ concentrations DNA aggregation was observed.

High-Mobility Group (HMG) chromosomal proteins are the most numerous nuclear non-histone proteins. HMGB domain proteins are the most abundant and well-studied HMG proteins. They are involved in variety of biological processes. HMGB1 and HMGB2 were the first members of HMGB-family to be discovered and are found in all studied eukaryotes. Despite the high degree of homology, HMGB1 and HMGB2 proteins differ from each other both in structure and functions. In contrast to HMGB2, there is a large pool of works devoted to the HMGB1 protein whose structure–function properties have been described in detail in our previous review in 2020. In this review, we attempted to bring together diverse data about the structure and functions of the HMGB2 protein. The review also describes post-translational modifications of the HMGB2 protein and its role in the development of a number of diseases. Particular attention is paid to its interaction with various targets, including DNA and protein partners. The influence of the level of HMGB2 expression on various processes associated with cell differentiation and aging and its ability to mediate the differentiation of embryonic and adult stem cells are also discussed.

The functioning of DNA in the cell nucleus is ensured by a multitude of proteins, whose interactions with DNA as well as with other proteins lead to the formation of a complicated, organized, and quite dynamic system known as chromatin. This review is devoted to the description of properties and structure of the progenitors of the most abundant non-histone protein of the HMGB family—the HmgB1 protein. The proteins of the HMGB family are also known as “architectural factors” of chromatin, which play an important role in gene expression, transcription, DNA replication, and repair. However, as soon as HmgB1 goes outside the nucleus, it acquires completely different functions, post-translational modifications, and change of its redox state. Despite a lot of evidence of the functional activity of HmgB1, there are still many issues to be solved related to the mechanisms of the influence of HmgB1 on the development and treatment of different diseases—from oncological and cardiovascular diseases to pathologies during pregnancy and childbirth. Here, we describe molecular structure of the HmgB1 protein and discuss general mechanisms of its interactions with other proteins and DNA in cell.

Non-histone nuclear proteins HMGB1 and HMGB2 (High Mobility Group) are involved in many biological processes, such as replication, transcription, and repair. The HMGB1 and HMGB2 proteins consist of a short N-terminal region, two DNA-binding domains, A and B, and a C-terminal sequence of glutamic and aspartic acids. In this work, the structural organization of calf thymus HMGB1 and HMGB2 proteins and their complexes with DNA were studied using UV circular dichroism (CD) spectroscopy. Post-translational modifications (PTM) of HMGB1 and HMGB2 proteins were determined with MALDI mass spectrometry. We have shown that despite the similar primary structures of the HMGB1 and HMGB2 proteins, their post-translational modifications (PTMs) demonstrate quite different patterns. The HMGB1 PTMs are located predominantly in the DNA-binding A-domain and linker region connecting the A and B domains. On the contrary, HMGB2 PTMs are found mostly in the B-domain and within the linker region. It was also shown that, despite the high degree of homology between HMGB1 and HMGB2, the secondary structure of these proteins is also slightly different. We believe that the revealed structural properties might determine the difference in the functioning of the HMGB1 and HMGB2 as well as their protein partners.

We have studied structural changes in DNA/protein complexes using the CD spectroscopy, upon the interaction of HMG1-domains with calf thymus DNA at different ionic strengths. HMG1 protein isolated from calf thymus and recombinant HMG1-(A+B) protein were used. Recombinant protein HMG1-(A+B) represents a rat HMG1 lacking C-terminal acidic tail. At low ionic strength (15 mM NaCl) we observed similar behavior of both proteins upon interaction with DNA. Despite this, at higher ionic strength (150 mM NaCl) their interaction with DNA leads to a completely different structure of the complexes. In the case of HMG1-(A+B)/DNA complexes we observed the appearance of DNA fractions possessing very high optical activity. This could be a result of formation of the highly-ordered DNA structures modulated by the interaction with HMG1-domains. Thus the comparison studies of HMG1 and HMG1-(A+B) interaction with DNA show that negatively charged C-terminal tail of HMG1 modulates interaction of the protein with DNA. The striking difference of the behaviour of these two systems allows us to explain the functional role of multiple HMG1 domains in some regulatory and architectural proteins.