Molecular Cryo-Electron Microscopy Unit, Okinawa Institute of Science and Technology Graduate University, Onna-son, Japan.
Department of Microbiology and Oral Infection, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
Nat Microbiol. 2020 Jun;5(6):830-837. doi: 10.1038/s41564-020-0705-1. Epub 2020 Apr 13.
Bacterial adhesion is a general strategy for host-microbe and microbe-microbe interactions. Adhesive pili are essential for colonization, biofilm formation, virulence and pathogenesis of many environmental and pathogenic bacteria. Members of the class Bacteroidia have unique type V pili, assembled by protease-mediated polymerization. Porphyromonas gingivalis is the main contributor to periodontal disease and its type V pili are a key factor for its virulence. However, the structure of the polymerized pilus and its assembly mechanism are unknown. Here we show structures of polymerized and monomeric states of FimA stalk pilin from P. gingivalis, determined by cryo-electron microscopy and crystallography. The atomic model of assembled FimA shows that the C-terminal strand of a donor subunit is inserted into a groove in the β-sheet of an acceptor subunit after N-terminal cleavage by the protease RgpB. The C terminus of the donor strand is essential for polymerization. We propose that type V pili assemble via a sequential polar assembly mechanism at the cell surface, involving protease-mediated strand exchange, employed by various Gram-negative species belonging to the class Bacteroidia. Our results reveal functional surfaces related to pathogenic properties of polymerized FimA. These insights may facilitate development of antibacterial drugs.
细菌黏附是宿主-微生物和微生物-微生物相互作用的一种通用策略。黏附性菌毛对于许多环境和致病性细菌的定植、生物膜形成、毒力和发病机制是必不可少的。拟杆菌门的成员具有独特的 V 型菌毛，由蛋白酶介导的聚合组装而成。牙龈卟啉单胞菌是牙周病的主要病原体，其 V 型菌毛是其毒力的关键因素。然而，聚合菌毛的结构及其组装机制尚不清楚。在这里，我们通过冷冻电子显微镜和晶体学确定了牙龈卟啉单胞菌 FimA 菌毛主干钉蛋白的聚合和单体状态的结构。组装后的 FimA 的原子模型表明，在蛋白酶 RgpB 对 N 端进行切割后，供体亚基的 C 端链被插入到受体亚基的β-折叠中的一个凹槽中。供体链的 C 端对于聚合是必需的。我们提出 V 型菌毛通过在细胞表面的顺序极性组装机制进行组装，涉及蛋白酶介导的链交换，这一机制被属于拟杆菌门的各种革兰氏阴性物种所采用。我们的研究结果揭示了与聚合 FimA 的致病性特性相关的功能表面。这些见解可能有助于开发抗菌药物。
