5gt3
From Proteopedia
Crystal structure of nucleosome particle in the presence of human testis-specific histone variant, hTh2b
Structural highlights
Function[H2B1A_HUMAN] Variant histone specifically required to direct the transformation of dissociating nucleosomes to protamine in male germ cells. Entirely replaces classical histone H2B prior nucleosome to protamine transition and probably acts as a nucleosome dissociating factor that creates a more dynamic chromatin, facilitating the large-scale exchange of histones. Also expressed maternally and is present in the female pronucleus, suggesting a similar role in protamine replacement by nucleosomes at fertilization (By similarity). Also found in fat cells, its function and the presence of post-translational modifications specific to such cells are still unclear. Core component of nucleosome. Nucleosomes wrap and compact DNA into chromatin, limiting DNA accessibility to the cellular machineries which require DNA as a template. Histones thereby play a central role in transcription regulation, DNA repair, DNA replication and chromosomal stability. DNA accessibility is regulated via a complex set of post-translational modifications of histones, also called histone code, and nucleosome remodeling.[1] [H2A1D_HUMAN] Core component of nucleosome. Nucleosomes wrap and compact DNA into chromatin, limiting DNA accessibility to the cellular machineries which require DNA as a template. Histones thereby play a central role in transcription regulation, DNA repair, DNA replication and chromosomal stability. DNA accessibility is regulated via a complex set of post-translational modifications of histones, also called histone code, and nucleosome remodeling. Publication Abstract from PubMedTh2a and Th2b are the testis-specific histone variants highly expressed during spermatogenesis. Approximately 4% of the genome is retained in nucleosomes in mature human sperm, which is enriched at loci of developmental importance. Our recent studies revealed that the mouse histone variant homologs TH2a and TH2b are involved in reprogramming. In the present work, we report three nucleosome structures (NCPs) with human testis-specific histone variants hTh2a and hTh2b, [hGcH (hTh2a-hTh2b-H3-H4), hGcHV1 (hTh2a-H2b-H3-H4) and hGcHV2 (H2a-hTh2b-H3-H4)] and a 146-base pair (bp) duplex DNA fragment at ~3.0A resolutions. These crystal structures revealed two major changes within the nucleosomes, either with hTh2a, hTh2b or both variants, as compared to the canonical counterpart. First, the H-bonding interactions between the L1-L1' interfaces mediated by the hTh2a/hTh2a' L1-loops are lost. Second, the histone dimer-DNA contacts are considerably reduced, and these changes are localized around +/-31 to 35-bp from the nucleosome entry/exit sites. Thus, the modified functional residues at the N- and C-terminal ends of histone variants are responsible for the observed structural changes and regulate the gene expression through specific structural alterations in the chromatin by modulating the chromatin-associated binding proteins. Structural analyses of the nucleosome complexes with human testis-specific histone variants, hTh2a and hTh2b.,Padavattan S, Thiruselvam V, Shinagawa T, Hasegawa K, Kumasaka T, Ishii S, Kumarevel T Biophys Chem. 2017 Feb;221:41-48. doi: 10.1016/j.bpc.2016.11.013. Epub 2016 Dec, 5. PMID:27992841[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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