The Structural Organization of the HMGB1 Nuclear Protein and Its Effect on the Formation of Ordered Supramolecular Complexes

Biophysics - HMGB1 is one of the key proteins of the cell. HMGB1 performs its main functions predominantly in the cell nucleus, as an essential component of DNA–protein and multiprotein...     

The effect of manganese(II) on DNA structure: electronic and vibrational circular dichroism studies

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.     

Conformational properties of nuclear protein HMGB1 and specificity of its interaction with DNA

Changes in secondary structure of DNA and non-histone chromosomal protein HMGB1 during the formation of the complex have been studied by circular dichroism and UV spectroscopy. It was demonstrated that the HMGB1 protein is able to change its secondary structure upon binding to DNA. Based on the assumption that there are two spectroscopically distinguishable forms of the HMGB1 in solution, we estimated the fraction of bound protein. The fraction of bound protein decreases at higher protein to DNA ratios r from 0.48 at r = 0.13 to 0.06 at r = 2.43. It was shown that HMGB1 is able to induce considerable changes in DNA structure, even when the amount of protein actually bound is low.     

Interaction of DNA with sperm-specific histones of the H1 family

Interactions of DNA with sperm-specific histones of the H1 family of sea urchin Strongylocentrotus intermedius, sea star Aphelasterias japonica, and bivalve mollusc Chlamis islandicus were studied using circular dichroism and the DNA melting analysis. Under physiological conditions, the highest DNA compacting ability was found in the echinoderm sperm H1 protein, in which additional α-helical domains are present in their C-terminal sequence. The derivative melting curves have two peaks: the low-temperature peak corresponds to the melting of free DNA, whereas the DNA regions bound to the protein melt at higher temperature. The highest stabilizing ability is characteristic of complexes with the mollusc sperm H1 protein.     

The effect of manganese(II) on the structure of DNA/HMGB1/H1 complexes: electronic and vibrational circular dichroism studies

The interactions were studied of DNA with the nonhistone chromatin protein HMGB1 and histone H1 in the presence of manganese(II) ions at different protein to DNA and manganese to DNA phosphate ratios by using absorption and optical activity spectroscopy in the electronic [ultraviolet (UV) and electronic circular dichroism ECD)] and vibrational [infrared (IR) and vibrational circular dichroism (VCD)] regions. In the presence of Mn2+, the protein-DNA interactions differ from those without the ions and cause prominent DNA compaction and formation of large intermolecular complexes. At the same time, the presence of HMGB1 and H1 also changed the mode of interaction of Mn2+ with DNA, which now takes place mostly in the major groove of DNA involving N7(G), whereas interactions between Mn2+ and DNA phosphate groups are weakened by histone molecules. Considerable interactions were also detected of Mn2+ ions with aspartic and glutamic amino acid residues of the proteins.     

The Role of Linker Histones in Chromatin Structural Organization. 1. H1 Family Histones

Biophysics - Data on the role of H1 family linker histones in the structural organization and functioning of chromatin that have accumulated to date are presented in this review. The structure of...     

Structure of DNA complexes with chromosomal protein HMGB1 and histone H1 in the presence of manganese ions: 2. Vibrational circular dichroism spectroscopy

DNA complexes with nonhistone HMGB1 chromatin protein and histone H1 in the presence of manganese ions were studied using methods of absorption and circular dichroism spectroscopy in the infrared region. It was demonstrated that the method provides good results, even for solutions that contain large particles, which cause scattering in UV region. It was determined that manganese ions in the complex are able to coordinate not only to different chemical groups in DNA, but also to dicarboxylic acid residues of the HMGB1 protein, which stimulates DNA condensation and slightly weakens DNA-protein interactions in the complex.     

Analysis of the secondary structure of linker histone H1 based on IR absorption spectra

The effectiveness is compared of the infrared spectroscopy in the amide I region and UV circular dichroism to the analysis of the protein secondary structure by the example of the linker histone H1 and bovine serum albumin (BSA). It has been shown that the application of a diamond ATR cell gives the quantitative estimate of the fraction of α-helices and β-structures which are in a good agreement with UV circular dichroism spectroscopy. It has been shown that the histone H1 is able to aggregate, which results in considerable changes in its secondary structure.     

Investigation of DNA Damage Induced by Proton and Gamma Radiation

Biophysics - In this study, we compared the effects of gamma and high-energy proton radiation (1000 MeV) on DNA in aqueous saline solutions (5 and 150 mM NaCl) at doses of 30 and 50 Gy. We used...     

Structure of DNA complexes with chromosomal protein HMGB1 and histone H1 in the presence of manganese ions: 1. Circular dichroism spectroscopy

Mechanisms of interaction of DNA with nonhistone chromosomal protein HMGB1 and linker histone H1 have been studied by means of circular dichroism and absorption spectroscopy. Both proteins are located in the internucleosomal regions of chromatin. It is demonstrated that the properties of DNA-protein complexes depend on the protein content and cannot be considered as a mere summing up of the effects of individual protein components. Interaction of the HMGB1 and H1 proteins is shown with DNA to be cooperative rather than competitive. Lysine-rich histone H1 facilitates the binding of HMGB1 to DNA by screening the negatively charged groups of the sugar-phosphate backbone of DNA and dicarboxylic amino acid residues in the C-terminal domain of HMGB1. The observed joint action of HMGB1 and H1 stimulates DNA condensation with the formation of anisotropic DNA-protein complexes with typical ψ-type CD spectra. Structural organization of the complexes depends not only on DNA-protein interactions but also on interaction between the HMGB1 and H1 protein molecules bound to DNA. Manganese ions significantly modify the mode of interactions between components in the triple DNA-HMGB1-H1 complex. The binding of Mn²⁺ ions weakens DNA-protein interactions and strengthens protein-protein interactions, which promote DNA condensation and formation of large DNA-protein particles in solution.