牙龈卟啉单胞菌第Ⅸ型分泌系统结构与功能研究进展

Research progress on the structure and function of the type IX secretion system of Porphyromonas gingivalis

牙龈卟啉单胞菌第Ⅸ型分泌系统(type Ⅸ secretion system,T9SS)是一种最近被发现的新型蛋白分泌系统,它广泛分布于拟杆菌中。T9SS结构复杂、功能强大,目前已经得到验证的T9SS组分20余种,并且仅在牙龈卟啉单胞菌中即能分泌30余种毒力因子,对牙龈卟啉单胞菌的致病性意义重大。T9SS是一个横跨细胞内膜、细胞周质、细胞外膜的大型蛋白复合体,通过各组分之间结构和功能上的联系,组成了一个包括动力提供、能量转导、内外膜易位、外膜修饰及调节系统的精密功能复合体,对货物蛋白进行识别、转运、剪切、修饰,并将细菌胞内货物蛋白转运至细胞表面。近年来,随着X线衍射及原位冷冻电镜技术的发展,对T9SS的探究也从单一组分的功能研究发展至多蛋白复合体原位结构研究,但是目前对蛋白结构解析仍存在分辨率不高、无法捕捉动态功能结构等问题,未来研究方向应该更集中于探索T9SS如何与货物蛋白相互作用并发挥功能。本文对牙龈卟啉单胞菌T9SS在X线衍射及冷冻电镜结构解析上的研究进展做一综述,以便深入理解T9SS的转运机制。

The Porphyromonas gingivalis type IX secretion system(T9SS)is a recently discovered protein secretion system that is widely distributed in Bacillus cereus.The T9SS is structurally complex and powerful.More than 20 T9SS components have been verified,and more than 30 virulence factors can be secreted by Porphyromonas gingivalis alone,which contributes significant to the pathogenicity of Porphyromonas gingivalis.T9SS is a large protein complex spanning the inner cell membrane,periplasm,and outer cell membrane.Through the structural and functional connections among its components,it forms a sophisticated functional complex that includes power provision,energy transduction,inner and outer membrane translocation,outer membrane modification,and regulatory systems to recognize,translocate,shear,and modify cargo proteins and translocate bacterial intracellular cargo proteins to the cell surface.In recent years,with advancements in X-ray diffraction and in situ cryoelectron microscopy,the exploration of T9SS has evolved from the functional study of single components to the in situ structural study of multiprotein complexes.Still,the structural resolution of the protein still has shortcomings such as low resolution and an inability to capture dynamic functional structures.Future research directions should focus more on exploring how T9SS interacts and functions with cargo proteins.In this paper,we review the research progress on Porphyromonas gingivalis T9SS on X-ray diffraction and cryo-electron microscopy structure resolution in order to gain a deeper understanding of the transport mechanism of T9SS.