Structure Of Histone H3 Research Articles

Microgravity-Induced Alterations in the H3.3B (H3F3B) Gene Expression and the Histone H3 Structure

It has been believed that microgravity directly can modify the structure, function, and morphology of biosystems and numerous researches have been performed to recognize these alterations. Since histone H3 is an essential protein in the field of epigenetics, this research aimed to evaluate the effects of simulated microgravity on the human H3.3B (H3F3B) gene expression and histone H3 structure. The two-dimensional clinostat was applied for simulating microgravity. Analysis of the gene expression by real-time quantitative PCR revealed that simulated microgravity diminished the expression level of H3.3B considerably (P < 0.001). The UV-Visible absorption and extrinsic fluorescence emission results displayed that after 72 h of simulated microgravity the tertiary structure of histone H3 changed and the surface hydrophobicity of the protein incremented remarkably. Nevertheless, circular dichroism (CD) data showed that simulated microgravity did not perturb the secondary structure of histone H3. Collectively, microgravity can strictly affect the gene expression level of H3.3. Furthermore, histone H3 72 h after subjecting to simulated microgravity can exhibit a molten globule structure. The significance of this research lied in the fact that simulating microgravity can be an effective physical force in gene expression regulation and the protein folding process. This finding could help astrobiologists to realize major health risks for astronaut crews and space travelers and reduce these harmful effects. Furthermore, our observations can open fascinating research lines in astrobiology, biophysics, and exobiology.

Biochemical Analysis Reveals the Multifactorial Mechanism of Histone H3 Clipping by Chicken Liver Histone H3 Protease.

Proteolytic clipping of histone H3 has been identified in many organisms. Despite several studies, the mechanism of clipping, the substrate specificity, and the significance of this poorly understood epigenetic mechanism are not clear. We have previously reported histone H3 specific proteolytic clipping and a protein inhibitor in chicken liver. However, the sites of clipping are still not known very well. In this study, we attempt to identify clipping sites in histone H3 and to determine the mechanism of inhibition by stefin B protein, a cysteine protease inhibitor. By employing site-directed mutagenesis and in vitro biochemical assays, we have identified three distinct clipping sites in recombinant human histone H3 and its variants (H3.1, H3.3, and H3t). However, post-translationally modified histones isolated from chicken liver and Saccharomyces cerevisiae wild-type cells showed different clipping patterns. Clipping of histone H3 N-terminal tail at three sites occurs in a sequential manner. We have further observed that clipping sites are regulated by the structure of the N-terminal tail as well as the globular domain of histone H3. We also have identified the QVVAG region of stefin B protein to be very crucial for inhibition of the protease activity. Altogether, our comprehensive biochemical studies have revealed three distinct clipping sites in histone H3 and their regulation by the structure of histone H3, histone modifications marks, and stefin B.