人源HDAC1/2-RbAp46/48核心复合物三维空间构象的电子显微分析

HDAC1、HDAC2和RbAp46、RbAp48是许多重要功能复合物(如NuRD、Sin3等)的核心亚基.这4个亚基在空间上相互作用,形成一个具有去乙酰化酶活性的核心复合物.但该核心复合物的三维空间构象及其对去乙酰化、染色质重塑等功能的可能影响还所知甚少.本研究中,我们包装了含4个亚基的杆状病毒,利用昆虫细胞表达、纯化了HDAC1/2-RbAp46/48核心复合物.在此基础上,利用电子显微镜单颗粒分析方法对该去乙酰化酶核心复合物的三维结构进行了初步解析.结果表明,HDAC1、HDAC2、RbAp46和RbAp48可以形成一个较为稳定均一的复合物,但该复合物中各个亚基并不是以单拷贝、等比例形式存在的.该核心复合物呈现一个非对称的鞍型结构,其背部隆起,大致形成一个三角形,两边分别有一大一小的两翼,两翼中间有个凹槽,直径大约为6 nm,推测为该核心复合物与核小体的结合位置.本研究结果为了解HDAC1/2-RbAp46/48去乙酰化酶复合物各亚基的空间结构组成、与核小体和染色质的可能相互作用以及研究去乙酰化酶活性的作用机理等提供了有益的信息.

Architecture of Human HDAC1/2-RbAp46/48 Core Protein Complex Revealed by Electron Microscopy

HDAC1, HDAC2 and RbAp46, RbAp48 are core subunits of several important functional molecular complexes, such as NuRD, Sin3. The four subunits interact with each other, forming a complex which has enzyme activity of deacetylation. However, little is known about the overall structure of this core complex and the influences of its structure to the chromatin deacetylation and remodeling activities. Here, we purified the HDAC1/2-RbAp46/48 core complex from the Sf9 cells infected with baculoviruses containing the genes of HDAC1, HDAC2, RbAp46, and RbAp48, and reconstructed the three dimensional architecture of the core complex using negative stain electron microscopic single particle analysis. It is found that the four subunits (HDAC1, HDAC2, RbAp46 RbAp48) can form a stable and uniform complex, but not all of the subunits exist in the form of a single copy or a proportion way in the the complex. It is shown that HDAC1/2-RbAp46/48 core complex presents an asymmetric saddle shape with a triangle shape back bulging. There is a groove, approximately 6 nm in width, in the middle of the wings of the saddle. We hypothesize that the groove is the binding site of the nucleosome, although further analysis is needed. The work reported here sheds a light on the overall structure of the HDAC1/2-RbAp46/48 complex and its interaction with nucleosome and chromatin, and the mechanism of deactylation enzyme activity of this core complex.