Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, United States.
Department of Biochemistry and Biophysics, Rochester University Medical Center, Rochester, NY 14625, United States.
J Mol Biol. 2023 Oct 1;435(19):168242. doi: 10.1016/j.jmb.2023.168242. Epub 2023 Aug 23.
The highly positively charged and intrinsically disordered H1 C-terminal domain (CTD) undergoes extensive condensation upon binding to nucleosomes, and stabilizes nucleosomes and higher-order chromatin structures but its interactions in chromatin are not well defined. Using single-molecule FRET we found that about half of the H1 CTDs in H1-nucleosome complexes exhibit well-defined FRET values indicative of distinct, static conformations, while the remainder of the population exhibits exchange between multiple defined FRET structures. Moreover, crosslinking studies indicate that the first 30 residues of the H1 CTD participate in relatively localized contacts with the first ∼25 bp of linker DNA, and that two separate regions in the CTD contribute to H1-dependent organization of linker DNA. Finally, we show that acetylation mimetics within the histone H3 tail markedly reduce the overall extent of H1 CTD condensation and significantly increase the fraction of H1 CTDs undergoing dynamic exchange between FRET states. Our results indicate the nucleosome-bound H1 CTD adopts loosely defined structures that exhibit significantly enhanced dynamics and decondensation upon epigenetic acetylation within the H3 tail.
高度带正电荷且固有无序的 H1 羧基末端结构域（CTD）在与核小体结合时会发生广泛的凝聚，从而稳定核小体和更高阶的染色质结构，但它在染色质中的相互作用尚未得到很好的定义。我们使用单分子 FRET 发现，在 H1-核小体复合物中，大约有一半的 H1 CTD 表现出明确的 FRET 值，表明存在独特的静态构象，而其余部分则表现出多个定义的 FRET 结构之间的交换。此外，交联研究表明，H1 CTD 的前 30 个残基与连接 DNA 的前约 25bp 之间存在相对局部的接触，CTD 中的两个单独区域有助于 H1 依赖的连接 DNA 组织。最后，我们表明，组蛋白 H3 尾部内的乙酰化类似物显著降低了 H1 CTD 凝聚的整体程度，并显著增加了 H1 CTD 在 FRET 状态之间进行动态交换的比例。我们的结果表明，核小体结合的 H1 CTD 采用了松散定义的结构，在 H3 尾部的表观遗传乙酰化作用下，这些结构表现出显著增强的动力学和去凝聚作用。
