MapZ调控肺炎链球菌分裂环精确定位的分子机制

The human pathogen Streptococcus pneumoniae is responsible for many infectious diseases, such as pneumonia, otitis media and meningitis, leading to over 1.6 million deaths annually in the world. Its pathogenesisis strongly correlated with the process of cell division. Recently, the mid-cell-anchored protein Z (MapZ) was identified as a permanent beacon of division sites. MapZ forms ring structures at the cell equator and moves apart as the cell elongates. In addition, MapZ positions the FtsZ ring through direct protein–protein interactions, which initiates the assembly of divisome. As an exclusively conserved protein in Streptococci, MapZ probably confers a novel mechanism of precise localization of Streptococcal septal ring. In this project we will solve the structures of MapZ and the MapZ-FtsZ complex. We will also identify the target proteins and the specifically MapZ-recognized peptidoglycan fragments at the cell equator. These results will enable us to elucidate the fine molecular functions of MapZ and its ring-forming mechanism. Moreover, these findings will provide the structural insights into pneumococcal cell division and hints for rational design of inhibitors/vaccines against pneumococcal growth.

肺炎链球菌是引起人类肺炎、中耳炎和脑膜炎的主要致病菌，每年导致全球超过160万人死亡，其致病性与细胞分裂过程密切相关。最近发现MapZ蛋白(Mid-cell-anchored protein Z)标记细胞分裂位点，最先定位在分裂隔板上，然后招募FtsZ和其他蛋白组装成分裂体。MapZ作为链球菌中特有的蛋白，使得链球菌采用一种全新的机制识别分裂位点。本研究将利用X射线晶体学手段解析MapZ蛋白及其与FtsZ复合物的三维结构，并鉴定MapZ识别的靶蛋白和分裂隔板的肽聚糖序列，阐明MapZ的分子功能和成环机制，从原子分辨率水平上揭示肺炎链球菌细胞分裂环精确定位的分子机制。本研究将为研发防治肺炎链球菌的药物和疫苗提供结构基础。

根据本项目的任务目标，我们系统研究了肺炎链球菌MapZ对于细胞分裂蛋白FtsZ聚合及原丝纤维束形成的精细调控过程。我们发现MapZ胞内结构域MapZ-N可以与FtsZ形成稳定复合物，利用核磁共振滴定实验鉴定出9个关键残基。FtsZ酶活实验发现MapZ-N可以通过降低FtsZ的临界聚合浓度，缩短原丝纤维活化时间并提高FtsZ多聚体的协同作用来促进FtsZ形成原丝纤维。另外，FtsZ聚合实验表明MapZ-N通过与FtsZ亚基C末端竞争结合FtsZ核心结构域从而破坏FtsZ原丝纤维间的横向作用，进而抑制FtsZ原丝纤维束的形成。同时我们表达得到了稳定的细胞分裂复合体FtsE-FtsX以及肽聚糖水解酶PcsB，解析了PcsB的CHAP结构域的晶体结构。另外我们解析了肺炎链球菌辅助分泌系统SecA2/Y2中Asp1/2/3复合物的三维结构，结合生化实验阐明了Asp1/2/3对于底物蛋白糖基化和转运至关重要。总体来说，本项目完成了任务目标，研究成果进一步加深了对于肺炎链球菌细胞分裂调控的认识。