Howard Hughes Medical Institute, Colorado State University, Fort Collins, CO 80523, USA.
Mol Cell. 2013 Sep 12;51(5):662-77. doi: 10.1016/j.molcel.2013.07.015. Epub 2013 Aug 22.
The histone H2A-H2B heterodimer is an integral component of the nucleosome. The cellular localization and deposition of H2A-H2B into chromatin is regulated by numerous factors, including histone chaperones such as nucleosome assembly protein 1 (Nap1). We use hydrogen-deuterium exchange coupled to mass spectrometry to characterize H2A-H2B and Nap1. Unexpectedly, we find that at low ionic strength, the α helices in H2A-H2B are frequently sampling partially disordered conformations and that binding to Nap1 reduces this conformational sampling. We identify the interaction surface between H2A-H2B and Nap1 and confirm its relevance both in vitro and in vivo. We show that two copies of H2A-H2B bound to a Nap1 homodimer form a tetramer with contacts between H2B chains similar to those in the four-helix bundle structural motif. The organization of the complex reveals that Nap1 competes with histone-DNA and interhistone interactions observed in the nucleosome, thereby regulating the availability of histones for chromatin assembly.
组蛋白 H2A-H2B 异二聚体是核小体的一个组成部分。细胞内 H2A-H2B 定位于染色质和向染色质中沉积的过程受到许多因素的调控,包括核小体装配蛋白 1(Nap1)等组蛋白伴侣。我们使用氢氘交换结合质谱的方法来对 H2A-H2B 和 Nap1 进行分析。出人意料的是,我们发现,在低盐浓度下,H2A-H2B 的 α 螺旋经常呈现部分无序构象,而与 Nap1 结合则会减少这种构象的采样。我们确定了 H2A-H2B 与 Nap1 之间的相互作用表面,并通过体内和体外实验证实了其相关性。我们发现,两个 H2A-H2B 与一个 Nap1 同源二聚体结合形成四聚体,H2B 链之间的接触类似于四螺旋束结构基序。该复合物的结构揭示了 Nap1 与核小体中观察到的组蛋白-DNA 和组间相互作用竞争,从而调节组蛋白用于染色质组装的可用性。