Department of Microbiology and Oral Infection, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Nagasaki, Japan.
Molecular Cryo-Electron Microscopy Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, Japan.
Microbiol Immunol. 2020 Oct;64(10):643-656. doi: 10.1111/1348-0421.12838. Epub 2020 Sep 9.
Pili or fimbriae, which are filamentous structures present on the surface of bacteria, were purified from a periodontal pathogen, Porphyromonas gingivalis, in 1980s. The protein component of pili (stalk pilin), which is its major component, was named FimA; it has a molecular weight of approximately 41 kDa. Because the molecular weight of the pilin from P. gingivalis is twice that of pilins from other bacterial pili, the P. gingivalis Fim pili were suggested to be formed via a novel mechanism. In earlier studies, we reported that the FimA pilin is secreted on the cell surface as a lipoprotein precursor, and the subsequent N-terminal processing of the FimA precursor by arginine-specific proteases is necessary for Fim pili formation. The crystal structures of FimA and its related proteins were determined recently, which show that Fim pili are formed by a protease-mediated strand-exchange mechanism. The most recent study conducted by us, wherein we performed cryoelectron microscopy of the pilus structure, provided evidence in support of this mechanism. As the P. gingivalis Fim pili are formed through novel transport and assembly mechanisms, such pili are now designated as Type V pili. Surface lipoproteins, including the anchor pilin FimB of Fim pili that are present on the outer membrane, have been detected in certain Gram-negative bacteria. Here, we describe the assembly mechanisms of pili, including those of Type V and other pili, as well as the lipoprotein transport mechanisms.
在 20 世纪 80 年代，从牙周病原体牙龈卟啉单胞菌中纯化了存在于细菌表面的丝状结构——菌毛或纤毛。菌毛的蛋白质成分（主干菌毛蛋白）是其主要成分，它被命名为 FimA；其分子量约为 41 kDa。由于牙龈卟啉单胞菌菌毛的菌毛蛋白分子量是其他细菌菌毛菌毛蛋白的两倍，因此推测牙龈卟啉单胞菌 Fim 菌毛是通过一种新的机制形成的。在早期的研究中，我们报道了 FimA 菌毛蛋白作为脂蛋白前体在细胞表面分泌，随后由精氨酸特异性蛋白酶对 FimA 前体进行 N 端加工是 Fim 菌毛形成所必需的。最近，我们确定了 FimA 及其相关蛋白的晶体结构，表明 Fim 菌毛是通过蛋白酶介导的链交换机制形成的。我们最近进行的一项研究通过对菌毛结构进行低温电子显微镜观察，为该机制提供了证据。由于牙龈卟啉单胞菌 Fim 菌毛是通过新的运输和组装机制形成的，因此这些菌毛现在被指定为 V 型菌毛。某些革兰氏阴性菌的外膜上存在表面脂蛋白，包括 Fim 菌毛的锚定菌毛蛋白 FimB。在这里，我们描述了菌毛的组装机制，包括 V 型菌毛和其他菌毛的组装机制，以及脂蛋白的运输机制。
