Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Otto-Hahn-Straße 11, 44227, Dortmund, Germany.
Department of Chemical Biology, Max Planck Institute of Molecular Physiology, Otto-Hahn-Straße 11, 44227, Dortmund, Germany.
Nat Commun. 2019 Sep 6;10(1):4046. doi: 10.1038/s41467-019-12019-6.
Nucleosomes containing the histone H3 variant CENP-A are the epigenetic mark of centromeres, the kinetochore assembly sites required for chromosome segregation. HJURP is the CENP-A chaperone, which associates with Mis18α, Mis18β, and M18BP1 to target centromeres and deposit new CENP-A. How these proteins interact to promote CENP-A deposition remains poorly understood. Here we show that two repeats in human HJURP proposed to be functionally distinct are in fact interchangeable and bind concomitantly to the 4:2:2 Mis18α:Mis18β:M18BP1 complex without dissociating it. HJURP binds CENP-A:H4 dimers, and therefore assembly of CENP-A:H4 tetramers must be performed by two Mis18αβ:M18BP1:HJURP complexes, or by the same complex in consecutive rounds. The Mis18α N-terminal tails blockade two identical HJURP-repeat binding sites near the Mis18αβ C-terminal helices. These were identified by photo-cross-linking experiments and mutated to separate Mis18 from HJURP centromere recruitment. Our results identify molecular underpinnings of eukaryotic chromosome inheritance and shed light on how centromeres license CENP-A deposition.
含有组蛋白 H3 变体 CENP-A 的核小体是着丝粒的表观遗传标记，着丝粒是染色体分离所必需的动粒组装位点。HJURP 是 CENP-A 的伴侣蛋白，它与 Mis18α、Mis18β 和 M18BP1 结合，靶向着丝粒并沉积新的 CENP-A。这些蛋白质如何相互作用以促进 CENP-A 的沉积仍知之甚少。在这里，我们表明，人类 HJURP 中两个被认为具有不同功能的重复实际上是可互换的，并同时结合到 4:2:2 Mis18α:Mis18β:M18BP1 复合物上，而不会使其解离。HJURP 结合 CENP-A:H4 二聚体，因此 CENP-A:H4 四聚体的组装必须由两个 Mis18αβ:M18BP1:HJURP 复合物或同一复合物在连续回合中完成。Mis18α N 端尾巴阻塞了 Mis18αβ C 端螺旋附近的两个相同的 HJURP 重复结合位点。这些是通过光交联实验鉴定的，并通过突变将 Mis18 与 HJURP 着丝粒募集分开。我们的结果确定了真核染色体遗传的分子基础，并阐明了着丝粒如何许可 CENP-A 的沉积。
