Machida Shinichi, Sekine Satoshi, Nishiyama Yuuki, Horikoshi Naoki, Kurumizaka Hitoshi
Laboratory of Structural Biology, Graduate School of Advanced Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan.
Research Institute for Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan.
Open Biol. 2016 Jun;6(6). doi: 10.1098/rsob.160090.
Monoubiquitination is a major histone post-translational modification. In humans, the histone H2B K120 and histone H4 K31 residues are monoubiquitinated and may form transcriptionally active chromatin. In this study, we reconstituted nucleosomes containing H2B monoubiquitinated at position 120 (H2Bub120) and/or H4 monoubiquitinated at position 31 (H4ub31). We found that the H2Bub120 and H4ub31 monoubiquitinations differently affect nucleosome stability: the H2Bub120 monoubiquitination enhances the H2A-H2B association with the nucleosome, while the H4ub31 monoubiquitination decreases the H3-H4 stability in the nucleosome, when compared with the unmodified nucleosome. The H2Bub120 and H4ub31 monoubiquitinations both antagonize the Mg(2+)-dependent compaction of a poly-nucleosome, suggesting that these monoubiquitinations maintain more relaxed conformations of chromatin. In the crystal structure, the H2Bub120 and H4ub31 monoubiquitinations do not change the structure of the nucleosome core particle and the ubiquitin molecules were flexibly disordered in the H2Bub120/H4ub31 nucleosome structure. These results revealed the differences and similarities of the H2Bub120 and H4ub31 monoubiquitinations at the mono- and poly-nucleosome levels and provide novel information to clarify the roles of monoubiquitination in chromatin.
单泛素化是一种主要的组蛋白翻译后修饰。在人类中，组蛋白H2B的第120位赖氨酸（H2B K120）和组蛋白H4的第31位赖氨酸（H4 K31）会发生单泛素化，并且可能形成转录活性染色质。在本研究中，我们重构了在第120位发生单泛素化的H2B（H2Bub120）和/或在第31位发生单泛素化的H4（H4ub31）的核小体。我们发现，H2Bub120和H4ub31单泛素化对核小体稳定性的影响不同：与未修饰的核小体相比，H2Bub120单泛素化增强了H2A-H2B与核小体的结合，而H4ub31单泛素化降低了核小体中H3-H4的稳定性。H2Bub120和H4ub31单泛素化均拮抗多聚核小体的Mg(2+)依赖性压缩，这表明这些单泛素化维持了染色质更松散的构象。在晶体结构中，H2Bub120和H4ub31单泛素化不会改变核小体核心颗粒的结构，并且泛素分子在H2Bub120/H4ub31核小体结构中呈灵活无序状态。这些结果揭示了H2Bub120和H4ub31单泛素化在单核小体和多聚核小体水平上的差异和相似性，并为阐明单泛素化在染色质中的作用提供了新的信息。
