Mechanisms for Histone H2B Deubiquitination

 描述(由申请人提供)：组蛋白蛋白的翻译后修饰调节所有需要获得DNA的过程。小蛋白泛素与组蛋白H2B的结合是活跃转录基因的普遍特征，已被认为在染色质结构的动态变化中发挥作用。然而，对于酶如何调节这种修饰，以及泛素的附着和移除如何与核小体动力学相耦合，还缺乏机械上的理解。在阐明H2B泛素化如何调控转录的许多障碍中，缺乏对调节这一修饰的酶与其核小体底物结合的方式的分子洞察力。酵母中的H2B泛素化水平受两种去泛素化酶的调节：四蛋白SAGA DUB模块，它是1.9 MDA SAGA转录共激活复合体的一部分，以及Ubp10，一种单体酶。尽管DUB模块和Ubp10表面上都针对相同的底物进行泛素化，但任一enyzme的缺失在体内都有不同的影响，这表明这些酶要么针对不同的基因组位置，要么与染色质相互作用的方式不同。在过去的资助期间，我们成功地结晶了与泛素化核小体结合的SAGA Dub模块-Ubp8/Sgf11/Sus1/Sgf73。我们将在这一成就的基础上，解决H_2B泛素化是如何受到调控的，以及H_2B去泛素化如何与核小体动力学相耦合。在目标1中，我们将通过确定与泛素化核小体结合的Ubp8/Sgf11/Sus1/Sgf73的原子分辨结构来解决SAGA dub模块如何识别泛素化核小体。这些结果也将为探索与组蛋白H2A-Y58磷酸化的串扰如何调节酵母和人类细胞中的DuB模块活性提供基础。在目标2中，我们将确定Ubp10与染色质特异结合的机制，以及SAGA DUB模块和Ubp10与H2B结合的差异如何奠定它们不同的生物学功能。在目标3中，我们将探索组蛋白伴侣蛋白在调控Ubp10和其组蛋白底物的DUB模块的特异性中所起的作用。

 DESCRIPTION (provided by applicant): Post-translational modification of histone proteins regulates all processes requiring access to DNA. Attachment of the small protein, ubiquitin, to histone H2B is a universal feature of actively transcribed genes and has been proposed to play a role in dynamic changes in chromatin structure. However, a mechanistic understanding of how enzymes regulate this modification, and how attachment and removal of ubiquitin may be coupled to nucleosome dynamics, is lacking. Among many barriers to elucidating how H2B ubiquitination regulates transcription has been the lack of molecular insights into the way that enzymes that regulate this modification engage their nucleosome substrates. Levels of H2B ubiquitination in yeast are regulated by two deubiquitinating enzymes: the four-protein SAGA DUB module, which is part of the 1.9 MDa SAGA transcriptional coactivator complex, and Ubp10, a monomeric enzyme. Although both the DUB module and Ubp10 ostensibly target the same substrate for ubiquitination, deletion of either enyzme has a distinct effect in vivo, suggesting that these enzyme are either targeted to different genomic locations or interact differently with chromatin. In the past funding period, we succeeded in crystallizing the SAGA DUB module - Ubp8/Sgf11/Sus1/Sgf73 - bound to ubiquitinated nucleosomes. We will build upon this accomplishment to address how H2B ubiquitination is regulated and how H2B deubiquitination is coupled to nucleosome dynamics. In Aim 1, we will address how the SAGA DUB module recognizes ubiquitinated nucleosomes by determining the atomic resolution structure of Ubp8/Sgf11/Sus1/Sgf73 bound to ubiquitinated nucleosomes. These results will also provide a foundation for probing how cross-talk with phosphorylation of histone H2A-Y58 regulates DUB module activity in yeast and human cells. In Aim 2, we will determine the mechanism by which Ubp10 specifically engages chromatin and how differences between SAGA DUB module and Ubp10 binding to H2B might underlie their distinct biological functions. In Aim 3, we will explore the role that histone chaperones play in governing the specificity of both Ubp10 and the DUB module for their histone substrates.