新型泛素化修饰系统SidE及MavC催化和调控的分子机制研究

经典泛素化修饰依赖于E1-E2-E3级联反应。然而，来源于嗜肺军团菌的蛋白SidE和MavC却以全新的方式进行泛素化修饰。SidE以NAD为辅因子，将磷酸核糖化的泛素连接到底物丝氨酸上。MavC则通过对泛素40位的谷氨酰胺脱氨，将其连接到E2结合酶UBE2N的92位或94位的赖氨酸上。SidE和MavC的活性还受到嗜肺军团菌自身严密的调控。SidJ可拮抗SidE的活性，DupA和DupB可将SidE介导的泛素化修饰去泛素化；Lpg2149可抑制MavC的酶活，MvcA可将MavC介导的泛素化修饰去泛素化。然而，SidE和MavC催化和调控的分子机制尚不完全清楚。本项目将在前期工作的基础上，通过结构生物学并结合生物化学和细胞生物学等手段阐明SidE和MavC催化底物修饰及动态调控的分子基础。对这两种新型泛素化修饰系统的研究，不仅有助于拓宽对泛素化修饰的理解，还将对开发抗感染药物提供帮助。

Conventional ubiquitination is achieved by the E1-E2-E3 cascade reaction. Unexpectedly and interestingly, effector proteins SidE and MavC secreted by Legionella pneumophila can ubiquitinated substrates via novel reaction pattern. With NAD as the cofactor, SidE can conjugate phosphoribosylated ubiquitin to serine residues of substrates through a phosphodiester bond. MavC could catalyze ubiquitin covalently attached to the Lys92 or Lys94 of UBE2N via deaminizing Gln40 of ubiquitin molecule. Meanwhile, the activity of SidE and MavC are precisely and temporally regulated by Legionella pneumophila itself. SidJ from Legionella pneumophila could antagonize the activity of SidE, and DupA or DupB could deubiquitinate SidE-mediated ubiquitination. Lpg2149 can suppress MavC’s enzyme activity, and MvcA could remove ubiquitin from the ubiquitinated UBE2N modified by MavC. However, the molecular mechanisms of SidE’s and MavC’s catalysis and regulation are still not totally clear. Based on the preliminary data, this research program will combine approaches of structure biology, biochemical and cell biology to study the molecular basis and regulation network of these two kinds of novel ubiquitination system. The foreseeable progress on the novel ubiquitination systems will not only help to broaden the understanding of ubiquitination, but also provide a prompt for developing new anti-infectious drugs.