RING型E3酶泛素化核小体组蛋白的化学机制

Chemical mechanisms of nucleosomal histone ubiquitination by RING-type E3 enzymes

细胞内存在多种E3酶对核小体上不同赖氨酸位点进行选择性的泛素化,继而招募下游效应蛋白参与调控不同的细胞进程,如转录激活、基因沉默、DNA损伤修复等.近年来,复杂翻译后修饰蛋白质与其复合体化学合成技术的发展,及冷冻电子显微镜、核磁共振、交联质谱等生物物理技术的进步,促进了E3对核小体进行泛素化反应的化学机制的解析.本文综述了四种E3酶(PRC1、BRCA1/BARD1、RNF168和Bre1)对核小体底物进行特异性泛素化修饰的相关化学生物学、生物化学和结构生物学机制研究进展.这些E3酶均通过经典的“精氨酸锚”结合核小体酸性口袋进行定位,再借助E3酶与其他核心组蛋白以及E2酶与DNA等多价互作方式,控制E2酶的活性半胱氨酸朝向底物的特定泛素化位点,诱导泛素从E2酶向底物的位点特异性转移.这些研究揭示了E3酶选择性泛素化核小体的化学原理,阐明了核小体上位点特异性泛素化的生成机制,为设计药物小分子干预细胞内核小体泛素化水平及治疗相关疾病提供了结构基础.

Various E3 enzymes present in cells selectively ubiquitinate different lysine sites on the nucleosomes,recruiting downstream effector proteins to participate in the regulation of a variety of cellular processes,such as transcription activation,gene silencing,and DNA damage repair.Recently,the continuous development of chemical synthesis of complex post-translationally modified proteins and their complexes,as well as the advances in biophysical techniques such as cryo-electron microscopy,nuclear magnetic resonance and cross-linked mass spectrometry have promoted the elucidation of the chemical mechanism of nucleosome ubiquitination by E3 enzymes.This paper reviews the recent chemical,biochemical,and structural biological studies of four E3 enzymes for specific ubiquitination of nucleosome substrates,including PRC1,BRCA1/BARD1,RNF168,and Bre1.These E3 enzymes bind to acidic patch of nucleosome through the classical“arginine anchor”for localization.By multivalent interactions between E3 enzyme with other core histones and E2 enzyme with DNA,the active cysteine of E2 enzyme is oriented towards specific ubiquitinated sites of substrates,inducing the site-specific transfer of ubiquitin from E2 enzyme to the substrate lysine.These studies reveal the chemical basis of selective ubiquitination of nucleosomes by E3 enzymes,clarify the mechanism of site-specific ubiquitination on nucleosomes,and provide structural basis for the design of small drug molecules to intervene in the ubiquitination level of nucleosomes in cells to treat related diseases.