在癌细胞中发现了典型组蛋白 H3.1 Glu97 残基 (H3E97K) 的 Lys 突变。先前的生化分析表明，与野生型核小体相比，含有H3E97K突变的核小体极其不稳定。然而，H3E97K突变导致核小体不稳定的机制尚未阐明。在本研究中，含有H3E97K突变的核小体的冷冻电镜结构显示，H3E97K核小体的进入/退出DNA区域是无序的，可能是由于核小体DNA与H3 N末端区域的分离所致。这可能会改变分子内氨基酸与被替换的 H3 Lys97 残基的相互作用，从而诱导核小体突变位置周围的结构扭曲。与核小体 DNA 末端的灵活性和核小体的不稳定性一致，H3E97K 突变表现出接头组蛋白 H1 与核小体的结合减少、PRC2（兼性异染色质形成所必需的甲基转移酶）与多核小体的激活缺陷以及核小体转录的增强RNA 聚合酶 II。© 2024 作者。日本分子生物学会和约翰·威利出版的《基因到细胞》

The Lys mutation of the canonical histone H3.1 Glu97 residue (H3E97K) is found in cancer cells. Previous biochemical analyses revealed that the nucleosome containing the H3E97K mutation is extremely unstable as compared to the wild-type nucleosome. However, the mechanism by which the H3E97K mutation causes nucleosome instability has not been clarified yet. In the present study, the cryo-electron microscopy structure of the nucleosome containing the H3E97K mutation revealed that the entry/exit DNA regions of the H3E97K nucleosome are disordered, probably by detachment of the nucleosomal DNA from the H3 N-terminal regions. This may change the intra-molecular amino acid interactions with the replaced H3 Lys97 residue, inducing structural distortion around the mutated position in the nucleosome. Consistent with the nucleosomal DNA end flexibility and the nucleosome instability, the H3E97K mutation exhibited reduced binding of linker histone H1 to the nucleosome, defective activation of PRC2 (the essential methyltransferase for facultative heterochromatin formation) with a poly-nucleosome, and enhanced nucleosome transcription by RNA polymerase II.© 2024 The Author(s). Genes to Cells published by Molecular Biology Society of Japan and John Wiley & Sons Australia, Ltd.