Abstract：
The testis-specific histone variant H3T plays a crucial role in chromatin reorganization during spermatogenesis by destabilizing nucleosomes. However, the structure basis for the nucleosome instability driven by H3T is not fully understand. In this study, we determinate the crystal structure of H3T-H4 in complex with histone chaperone ASF1a at 2.8 Å resolution. Our findings reveal that H3T-H4 binds ASF1a similarly to the conventional H3.1-H4 complex. However, significant structural differences are observed in the H3 α1 helix, the N- and C-terminal region of α2, and N-terminal region of L2. These differences are driven by H3T-specific residues, particularly Val111. Unlike the smaller Ala111 in H3.1, we find that bulkier residue Val111 fits well within the ASF1-H3T-H4 complex, but is difficult to arrange in nucleosome structure. Given that H3.1-Ala111/H3T-Val111 is located at the DNA binding and tetramerization interface of H3-H4, it is likely that Ala111Val substitution will lead to the instability of the corresponding area in nucleosome, contributing to instability of H3T-containing nucleosome. These structural findings may elucidate the role of H3T in chromatin reorganization during spermatogenesis.
摘要：
睾丸特异性组蛋白变体H3T通过破坏核小体在精子发生过程中的染色质重组中起着至关重要的作用。然而,由H3T驱动的核小体不稳定性的结构基础尚不完全清楚。在这项研究中,我们确定了与组蛋白伴侣ASF1a配合物的H3T-H4的晶体结构，分辨率为2.8。我们的发现揭示H3T-H4与常规H3.1-H4复合物类似地结合ASF1a。然而,在H3α1螺旋中观察到显著的结构差异，α2的N端和C端区域，以及L2的N端区域。这些差异是由H3T特异性残基驱动的，尤其是Val111。与H3.1中较小的Ala111不同，我们发现较大的残基Val111很适合ASF1-H3T-H4复合物，但是很难在核小体结构中排列。鉴于H3.1-Ala111/H3T-Val111位于H3-H4的DNA结合和四聚化界面，因此Ala111Val取代可能会导致核小体中相应区域的不稳定，导致含H3T的核小体的不稳定性。这些结构发现可以阐明H3T在精子发生过程中染色质重组中的作用。
