肺炎链球菌PsrP及其糖基化和分泌转运途径中蛋白的结构与功能研究

The major human pathogen Streptococcus pneumoniae is responsible for many infectious diseases, leading to approximately 1.6 million deaths annually in the world.Owing to the abuse of the antibiotics,S. pneumoniae showed resistance to penicillium,as well as the multiple resistances to other antibiotics.The current vaccines could not efficiently prevent the S. pneumoniae infection.Thus it is urgent to develop new antibiotics and/or vaccines.The surface proteins,espceilly the glycoprotians on capsule of S. pneumoniae are essential for their pathogenesis either during colonization or the spread/invasion stages, and most are virulence factors. Thus much effort has been made for developing new drugs and vaccines based on these molecules.However, the effort was restrained for little knowledge of the structures and functions of these proteins.Serine-rich repeat glycoproteins (SRRPs) are a family of bacterial surface adhesins found in numerous Gram-positive pathogens. They have been shown to be important for bacterial colonization, biofilm formation and pathogenesis.The serine-rich repeat protein PsrP of S. pneumoniae is heavily O-glycosylated within the serine-rich repeat regions with a molecular weight of 2300 kDa. Glycosylation and biogenesis of this protein are mediated by a gene cluster of 17 genes located downstream of psrP, among which 10 genes are responsible for the glycosylation and the other 7 for the secretion of PsrP. To elucidate the mechanism of PsrP glycosylation and secretion, we will systematically solve the structures of all proteins encoded by this gene cluster, in addition to the structure of their protein-protein complexes.The findings will enable us to regulate the biogenesis process of PsrP and may provide structural inisghts for the development of new antibiotics and vaccines.

肺炎球菌是人类主要的致病菌之一，导致全世界每年约160万人死亡。由于抗生素的大量使用，肺炎球菌出现抗生素的多重耐药,而现有疫苗本身的缺陷也不能解决肺炎球菌性疾病的预防，因此开发新的抗生素和疫苗迫在眉睫。肺炎链球菌中的表面蛋白, 尤其是荚膜上的糖蛋白是细菌毒力和逃脱免疫系统的主要作用分子，因而成为药物靶标设计和疫苗研发的重点。但对它们的三维结构和功能知之甚少，大大限制了新药和疫苗的开发。富含丝氨酸的糖蛋白PsrP是一个定位在荚膜上的高度糖基化蛋白,它参与肺炎链球菌的定植和生物膜形成，是重要的毒力因子。位于同一基因簇上的17个基因参与其糖基化及转运分泌。我们系统研究该基因簇编码的每个蛋白以及其相互作用蛋白复合物的结构和功能，以理解PsrP糖基化和分泌转运的分子机制，并设计合适的抑制剂来调节PsrP的生物合成过程，以期最终阐明肺炎链球菌的致病机理。研究结果将为新型抗生素和疫苗的研发提供理论指导。

本研究以病原菌富含丝氨酸糖蛋白SRRP及其合成通路为研究目标，系统研究了SRRP的结构和功能以及糖基化通路。解析了金葡菌SRRP蛋白SraP的配体结合区的晶体结构，发现 SraP 对通过识别唾液酸化的受体，帮助金葡菌粘附宿主。解析了参与肺炎链球菌SRRP蛋白PsrP糖基化的糖基转移酶GtfA和GlyE的结构，发现各自具有一个新颖的结构域，参与识别底物蛋白PsrP。另外通过体内和体外糖基化实验，系统阐述了PsrP的糖基化通路，鉴定了基因簇上所有糖基转移酶的功能，阐明了PsrP糖基化多态性的分子机制。本课题的成果为研究糖蛋白的结构和功能提供了新的方法和思路，也为研发针对SRRP糖基化的药物提供了结构基础。