Section of Structural Biology, Department Infectious Disease, Faculty of Medicine, Imperial College London, London SW7 2AZ, UK.
Section of Structural Biology, Department Infectious Disease, Faculty of Medicine, Imperial College London, London SW7 2AZ, UK; Single Molecule Imaging Group, MRC Laboratory of Medical Sciences, Du Cane Road, London W12 0HS, UK.
Mol Cell. 2024 Oct 17;84(20):3871-3884.e9. doi: 10.1016/j.molcel.2024.08.015. Epub 2024 Sep 2.
The yeast SWR1 complex catalyzes the exchange of histone H2A/H2B dimers in nucleosomes with Htz1/H2B dimers. We use cryoelectron microscopy to determine the structure of an enzyme-bound hexasome intermediate in the reaction pathway of histone exchange, in which an H2A/H2B dimer has been extracted from a nucleosome prior to the insertion of a dimer comprising Htz1/H2B. The structure reveals a key role for the Swc5 subunit in stabilizing the unwrapping of DNA from the histone core of the hexasome. By engineering a crosslink between an Htz1/H2B dimer and its chaperone protein Chz1, we show that this blocks histone exchange by SWR1 but allows the incoming chaperone-dimer complex to insert into the hexasome. We use this reagent to trap an SWR1/hexasome complex with an incoming Htz1/H2B dimer that shows how the reaction progresses to the next step. Taken together the structures reveal insights into the mechanism of histone exchange by SWR1 complex.
酵母 SWR1 复合物催化核小体中组蛋白 H2A/H2B 二聚体与 Htz1/H2B 二聚体的交换。我们使用冷冻电子显微镜确定了组蛋白交换反应途径中酶结合的六聚体中间物的结构，其中在插入由 Htz1/H2B 组成的二聚体之前，已从核小体中提取出 H2A/H2B 二聚体。该结构揭示了 Swc5 亚基在稳定从六聚体的组蛋白核心中解开 DNA 方面的关键作用。通过在 Htz1/H2B 二聚体与其伴侣蛋白 Chz1 之间设计交联，我们表明这会阻止 SWR1 进行组蛋白交换，但允许进入的伴侣蛋白-二聚体复合物插入六聚体。我们使用该试剂捕获具有进入的 Htz1/H2B 二聚体的 SWR1/六聚体复合物，显示了反应如何进展到下一步。总之，这些结构揭示了 SWR1 复合物进行组蛋白交换的机制的见解。
