National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China.
National Laboratory for Condensed Matter Physics and Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Cell Rep. 2021 May 25;35(8):109183. doi: 10.1016/j.celrep.2021.109183.
The multisubunit chromatin remodeler SWR1/SRCAP/p400 replaces the nucleosomal H2A-H2B dimer with the free-form H2A.Z-H2B dimer, but the mechanism governing the unidirectional H2A-to-H2A.Z exchange remains elusive. Here, we perform single-molecule force spectroscopy to dissect the disassembly/reassembly processes of the H2A nucleosome and H2A.Z nucleosome. We find that the N-terminal 1-135 residues of yeast SWR1 complex protein 2 (previously termed Swc2-Z) facilitate the disassembly of nucleosomes containing H2A but not H2A.Z. The Swc2-mediated nucleosome disassembly/reassembly requires the inherently unstable H2A nucleosome, whose instability is conferred by three H2A α2-helical residues, Gly47, Pro49, and Ile63, as they selectively weaken the structural rigidity of the H2A-H2B dimer. It also requires Swc2-ZN (residues 1-37) that directly anchors to the H2A nucleosome and functions in the SWR1-catalyzed H2A.Z replacement in vitro and yeast H2A.Z deposition in vivo. Our findings provide mechanistic insights into how the SWR1 complex discriminates between the H2A nucleosome and H2A.Z nucleosome, establishing a simple paradigm for the governance of unidirectional H2A.Z exchange.
多亚基染色质重塑复合物 SWR1/SRCAP/p400 用游离形式的 H2A.Z-H2B 二聚体取代核小体中的 H2A-H2B 二聚体，但控制 H2A 单向到 H2A.Z 交换的机制仍难以捉摸。在这里，我们进行了单分子力谱分析，以剖析 H2A 核小体和 H2A.Z 核小体的拆卸/组装过程。我们发现酵母 SWR1 复合物蛋白 2 的 N 端 1-135 个残基（先前称为 Swc2-Z）有助于含有 H2A 的核小体的拆卸，但不促进 H2A.Z 核小体的拆卸。Swc2 介导的核小体拆卸/组装需要固有不稳定的 H2A 核小体，其不稳定性由三个 H2Aα2-螺旋残基 Gly47、Pro49 和 Ile63 赋予，因为它们选择性地削弱了 H2A-H2B 二聚体的结构刚性。它还需要 Swc2-ZN（残基 1-37），它直接锚定在 H2A 核小体上，并在体外 SWR1 催化的 H2A.Z 取代和体内酵母 H2A.Z 沉积中发挥作用。我们的发现为 SWR1 复合物如何区分 H2A 核小体和 H2A.Z 核小体提供了机制上的见解，为单向 H2A.Z 交换的治理建立了一个简单的范例。
