Abstract
Clipping of histone tails has been reported in several organisms. However, the significance and regulation of histone tail clipping largely remains unclear. According to recent discoveries H3 clipping has been found to be involved in regulation of gene expression and chromatin dynamics. Earlier we had provided evidence of tissue-specific proteolytic processing of histone H3 in White Leghorn chicken liver nuclei. In this study we identify a novel activity of glutamate dehydrogenase (GDH) as a histone H3-specific protease in chicken liver tissue. This protease activity is regulated by divalent ions and thiol-disulfide conversion in vitro. GDH specifically clips H3 in its free as well as chromatin-bound form. Furthermore, we have found an inhibitor that inhibits the H3-clipping activity of GDH. Like previously reported proteases, GDH too may have the potential to regulate/modulate post-translational modifications of histone H3 by removing the N-terminal residues of the histone. In short, our findings identify an unexpected proteolytic activity of GDH specific to histone H3 that is regulated by redox state, ionic concentrations, and a cellular inhibitor in vitro.
Highlights
Histone H3 clipping has been reported in chicken liver tissues and not in brain
Because the preparation of nuclei by the ultracentrifugation method yields only a very small amount of pure nuclei, we found it more feasible to purify the protease from the microsomes, which could be prepared in larger amounts from the same amount of tissue
We found that GST-tails of all core histones inhibited the protease activity of glutamate dehydrogenase (GDH), which reveals that it probably interacts with all core histone tails but clips only H3 (Fig. 8, E–H)
Summary
Results: Glutamate dehydrogenase (GDH) is a histone H3-specific protease that clips free and chromatin-bound histone H3. In this study we identify a novel activity of glutamate dehydrogenase (GDH) as a histone H3-specific protease in chicken liver tissue. This protease activity is regulated by divalent ions and thiol-disulfide conversion in vitro. The regulation of chromatin structure is controlled by the dynamic interplay between sequence-specific DNA-binding proteins, histone variants, histone-modifying enzymes, chromatin-associated proteins, histone chaperones, ATP-dependent nucleosome remodelers, proteolytic clipping of histone tails, etc. We have identified a novel H3-clipping activity of GDH purified from RER that may regulate gene expression by modulating chromatin structure and function
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