Structure and Mechanism of Pathogen SET Domain HKMTs

描述（由申请人提供）：组蛋白的位点特异性翻译后修饰，包括甲基化、乙酰化、磷酸化和泛素化，作为组蛋白指导的染色质生物学中的基本表观遗传机制单独和/或组合发挥作用，其控制真核生物中的所有核DNA模板化过程。组蛋白赖氨酸甲基化几乎完全由SET结构域组蛋白赖氨酸甲基转移酶（HKMT）的大家族催化，其中一些与包括癌症和白血病在内的人类疾病有关。组蛋白赖氨酸甲基化通常比赖氨酸乙酰化更复杂，因为赖氨酸可以经历单甲基化、二甲基化或三甲基化，这在生物学背景下与不同的功能结果有着明显的联系。然而，这些组蛋白修饰酶的催化机制和底物特异性仍然没有得到很好的理解。值得注意的是，在这个广泛的蛋白质家族中，有一个由病毒和细菌编码的SET结构域蛋白质的亚类，包括炭疽芽孢杆菌，其是人类炭疽的已知病原体，但对其细胞功能知之甚少。我们目前的研究表明，从西氏杆菌病毒的SET结构域蛋白可能发挥作用，沉默宿主基因转录甲基化宿主组蛋白H3在赖氨酸27，一个修饰已知触发长期基因沉默在真核细胞。这些病原体SET结构域HKMT提供了极好的模型系统来表征SET结构域HKMT大家族的催化和底物特异性，以及研究病毒或细菌用于抑制宿主基因转录的可能的新机制。在本项目中，我们计划对一组来自炭疽芽孢杆菌和炭疽芽孢杆菌的SET结构域蛋白进行基于结构的分子和细胞生物学分析。我们的具体目标是解决这组病原体SET域HKMT的催化机制，甲基化多重性和位点特异性的分子基础的基本问题。虽然已知病毒募集细胞蛋白用于病毒基因组维持和复制，但病毒是否以及如何直接修饰宿主组蛋白以干扰宿主基因转录尚不清楚。因此，这些计划中的研究为我们提供了一个独特的机会，在宿主染色质水平上研究宿主-病原体相互作用，并获得这些病原体的生命周期，可能在相关人类疾病的分子发病机制中产生影响的新见解。

DESCRIPTION (provided by applicant): Site-specific post-translational modifications of histones that include methylation, acetylation, phosphorylation and ubiquitination function individually and/or combinatorially as fundamental epigenetic mechanisms in histone-directed chromatin biology that governs all nuclear DNA-templated processes in eukaryotic organisms. Histone lysine methylation is almost exclusively catalyzed by a large family of the SET domain histone lysine methyltransferases (HKMTs), some of which have been implicated in human diseases including cancers and leukemia. Histone lysine methylation is generally more complex than lysine acetylation, as a lysine can be subjected to mono-, di- or tri-methylation, which have been distinctively linked to different functional consequences in the biological context. However, the catalytic mechanism and substrate specificity of these histone modifying enzymes are still not well understood. Notably, within this extensive protein family there is a subclass of SET domain proteins that are encoded by viruses as well as bacteria, including Bacillus anthraces that are a known causative agent for anthrax in humans, but little is known about their cellular functions. Our current study suggests that the SET domain proteins from the chlorella viruses possibly play a role in silencing host gene transcription by methylating host histone H3 at lysine 27, a modification known to trigger long-term gene silencing in eukaryotic cells. These pathogen SET domain HKMTs offer excellent model systems to characterize the catalysis and substrate specificity for the large family of SET domain HKMTs, as well as to investigate possibly novel mechanisms by which viruses or bacteria use to suppress host gene transcription. In this Project, we plan to perform structure-based molecular and cellular biology analyses of a group of SET domain proteins from chlorella viruses and Bacillus anthracis. We specifically aim to address the fundamental questions of the molecular underpinnings concerning the catalytic mechanism, methylation multiplicity and site specificity of this group of pathogen SET domain HKMTs. While viruses are known to recruit cellular proteins for viral genome maintenance and replication, whether and how viruses directly modify host histones to interfere host gene transcription is not known. Therefore, these planned studies offer us with a unique opportunity to investigate host-pathogen interactions at host chromatin level, and to gain new insights into the life cycle of these pathogens that may have implications in the molecular pathogenesis in the related human diseases.