Post-translational modifications of linker histone H1 variants in mammals.

The covalent modifications of the linker histone H1 and the core histones are thought to play an important role in the control of chromatin functioning. Histone H1 variants from K562 cell line (hH1), mouse (mH1) and calf (cH1) thymi were studied by matrix-activated laser desorption/ionization fourier transform ion cyclotron resonance mass-spectroscopy (MALDI-FT-ICR-MS). The proteomics analysis revealed novel post-translational modifications of the histone H1, such as meK34-mH1.4, meK35-cH1.1, meK35-mH1.1, meK75-hH1.2, meK75-hH1.3, acK26-hH1.4, acK26-hH1.3 and acK17-hH1.1. The comparison of the hH1, mH1 and cH1 proteins has demonstrated that the types and positions of the post-translational modifications of the globular domains of the H1.2-H1.4 variants are very conservative. However, the post-translational modifications of the N- and C-terminal tails of H1.2, H1.3 and H1.4 are different. The differences of post-translational modifications in the N- and C-terminal tails of H1.2, H1.3 and H1.4 likely lead to the differences in DNA-H1 and H1-protein interactions.

INTERMOLECULAR INTERACTIONS IN THE SOLUTIONS OF SERUM ALBUMIN.

The mechanisms of intermolecular protein complex formation were studied by the example of monomers, oligomers and aggregates of bovine serum albumin (BSA) depending on the protein concentration, pH and urea concentration. Using dynamic light scattering (DLS), analytical ultracentrifugation (AUC) and PAG electrophoresis, we have shown that there is dynamic equilibrium between monomers and aggregates in BSA solution. Decreasing pH of the solution (4.0­1.0) resulted in increasing sizes of the aggregates. In the solutions with low urea concentrations (below 2 M), the sizes of aggregates decreased, while higher urea concentrations induced formation of larger aggregates due to the unfolding of the 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 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.