Chicken liver glutamate dehydrogenase (GDH) demonstrates a histone H3 specific protease (H3ase) activity in vitro

Site-specific proteolysis of the N or C-terminus of histone tails has emerged as a novel form of irreversible post-translational modifications assigned to histones. Though there are many reports describing histone specific proteolysis, there are very few studies on purification of a histone specific protease. Here, we demonstrate a histone H3 specific protease (H3ase) activity in chicken liver nuclear extract. H3ase was purified to homogeneity and identified as glutamate dehydrogenase (GDH) by sequencing. A series of biochemical experiments further confirmed that the H3ase activity was due to GDH. The H3ase clipped histone H3 products were sequenced by N-terminal sequencing and the precise clipping sites of H3ase were mapped. H3ase activity was only specific to chicken liver as it was not demonstrated in other tissues like heart, muscle and brain of chicken. We assign a novel serine like protease activity to GDH which is specific to histone H3.

Histone octamer trans-transfer: a signature mechanism of ATP-dependent chromatin remodelling unravelled in wheat nuclear extract

BACKGROUND AND SCOPE

In eukaryotes, chromatin remodelling complexes are shown to be responsible for nucleosome mobility, leading to increased accessibility of DNA for DNA binding proteins. Although the existence of such complexes in plants has been surmised mainly at the genetic level from bioinformatics studies and analysis of mutants, the biochemical existence of such complexes has remained unexplored.

METHODS

Histone H1-depleted donor chromatin was prepared by micrococcal nuclease digestion of wheat nuclei and fractionation by exclusion chromatography. Nuclear extract was partially purified by cellulose phosphate ion exchange chromatography. Histone octamer trans-transfer activity was analysed using the synthetic nucleosome positioning sequence in the absence and presence of ATP and its analogues. ATPase activity was measured as (32)Pi released using liquid scintillation counting.

KEY RESULTS

ATP-dependent histone octamer trans-transfer activity, partially purified from wheat nuclei using cellulose phosphate, showed ATP-dependent octamer displacement in trans from the H1-depleted native donor chromatin of wheat to the labelled synthetic nucleosome positioning sequence. It also showed nucleosome-dependent ATPase activity. Substitution of ATP by ATP analogues, namely ATPγS, AMP-PNP and ADP abolished the octamer trans-transfer, indicating the requirement of ATP hydrolysis for this activity.

CONCLUSIONS

ATP-dependent histone octamer transfer in trans is a recognized activity of chromatin remodelling complexes required for chromatin structure dynamics in non-plant species. Our results suggested that wheat nuclei also possess a typical chromatin remodelling activity, similar to that in other eukaryotes. This is the first report on chromatin remodelling activity in vitro from plants.

Anti-HIV and cytotoxic ruthenium(II) complexes containing flavones: biochemical evaluation in mice

Ru(II) polypyridyl complexes containing 3-hydroxyflavone derivatives as coligands were screened for anti-HIV and cytotoxic activities against eleven tumor cell lines. In order to check the effect of flavones containing Ru(II) complexes in vivo on a mammal, a representative complex Ru(L)2(DMSO)2 x 5H2O (LH-3-Hdroxy-4'-benzyloxyflavone; M5) was orally administered to adult male mice. Its effects on protein content and LDH were studied in different tissues of the animal. The compound got absorbed and retained in the blood between 1-3 hr after feeding. As compared to the normal and DMSO control sets, tissue specific significant reversible changes in the protein content as well as in LDH activity were observed between 1-4 hr of treatment. However, on polyacrylamide gel electrophoresis, except some tissue specific transitory alterations, expression patterns of five LDH isozymes were unchanged after feeding the compound. The present results suggested that in addition to its potent cytotoxic and anti-HIV effects on cell lines in vitro, M5 inhibited LDH activity, but reversibly with a little effect on biosynthetic status of the enzyme in mice.