Laboratory of Structural Biology, Graduate School of Advanced Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan.
Nature. 2011 Jul 10;476(7359):232-5. doi: 10.1038/nature10258.
In eukaryotes, accurate chromosome segregation during mitosis and meiosis is coordinated by kinetochores, which are unique chromosomal sites for microtubule attachment. Centromeres specify the kinetochore formation sites on individual chromosomes, and are epigenetically marked by the assembly of nucleosomes containing the centromere-specific histone H3 variant, CENP-A. Although the underlying mechanism is unclear, centromere inheritance is probably dictated by the architecture of the centromeric nucleosome. Here we report the crystal structure of the human centromeric nucleosome containing CENP-A and its cognate α-satellite DNA derivative (147 base pairs). In the human CENP-A nucleosome, the DNA is wrapped around the histone octamer, consisting of two each of histones H2A, H2B, H4 and CENP-A, in a left-handed orientation. However, unlike the canonical H3 nucleosome, only the central 121 base pairs of the DNA are visible. The thirteen base pairs from both ends of the DNA are invisible in the crystal structure, and the αN helix of CENP-A is shorter than that of H3, which is known to be important for the orientation of the DNA ends in the canonical H3 nucleosome. A structural comparison of the CENP-A and H3 nucleosomes revealed that CENP-A contains two extra amino acid residues (Arg 80 and Gly 81) in the loop 1 region, which is completely exposed to the solvent. Mutations of the CENP-A loop 1 residues reduced CENP-A retention at the centromeres in human cells. Therefore, the CENP-A loop 1 may function in stabilizing the centromeric chromatin containing CENP-A, possibly by providing a binding site for trans-acting factors. The structure provides the first atomic-resolution picture of the centromere-specific nucleosome.
在真核生物中，有丝分裂和减数分裂期间染色体的准确分离是由动粒协调的，动粒是微管附着的独特染色体位点。着丝粒指定个体染色体上动粒形成的位置，并通过组装含有着丝粒特异性组蛋白 H3 变体 CENP-A 的核小体来进行表观遗传标记。尽管其潜在机制尚不清楚，但着丝粒的遗传可能由着丝粒核小体的结构决定。在这里，我们报告了含有 CENP-A 和其同源α-卫星 DNA 衍生物（147 个碱基对）的人着丝粒核小体的晶体结构。在人 CENP-A 核小体中，DNA 以左手方向缠绕在组蛋白八聚体周围，由每个组蛋白 H2A、H2B、H4 和 CENP-A 各两个组成。然而，与典型的 H3 核小体不同，只有 DNA 的中心 121 个碱基对可见。DNA 的两端的 13 个碱基对在晶体结构中不可见，并且 CENP-A 的αN 螺旋比已知对典型 H3 核小体中 DNA 末端取向很重要的 H3 短。CENP-A 和 H3 核小体的结构比较表明，CENP-A 在 loop 1 区域含有两个额外的氨基酸残基（Arg80 和 Gly81），该区域完全暴露于溶剂中。CENP-A loop 1 残基的突变降低了人细胞中 CENP-A 在着丝粒上的保留。因此，CENP-A loop 1 可能通过为反式作用因子提供结合位点，在稳定含有 CENP-A 的着丝粒染色质中发挥作用。该结构提供了第一个原子分辨率的着丝粒特异性核小体的图片。
