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Biophys Chem. 2017 Feb;221:41-48. doi: 10.1016/j.bpc.2016.11.013. Epub 2016 Dec 5.

Structural analyses of the nucleosome complexes with human testis-specific histone variants, hTh2a and hTh2b.

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RIKEN SPring-8 Center, Harima Institute, 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan.
Centre of Advanced Study in Crystallography and Biophysics, University of Madras, Guindy Campus, Chennai 600 025, India.
Laboratory of Molecular Genetics, CREST Research Project of JST (Japan Science and Technology Agency), RIKEN Tsukuba Institute, 3-1-1 Koyadai, Tsukuba, Ibaraki 305-0074, Japan.
Japan Synchrotron Radiation Research Institute (SPring-8), 1-1-1 Kouto, Sayo-cho, Sayo-kun, Hyogo 679-5198, Japan.
RIKEN SPring-8 Center, Harima Institute, 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan; Structural Biology Laboratory, RIKEN Yokohama Institute, 1-7-22 Suehiro-cho, Tsurumi, Yokohama, Kanagawa 230-0045, Japan. Electronic address:


Th2a 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 ~3.0Å 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.


Nucleosome; Reprogramming; Testis-specific histone variants; hTh2a; hTh2b

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