Zhang Kai, He Jun, Cantalano Claudio, Guo Youzhong, Liu Jun, Li Chunhao
Philips Institute for Oral Health Research, School of Dentistry, Virginia Commonwealth University, Richmond, VA, USA.
Department of Microbial Pathogenesis, Microbial Sciences Institute, Yale University School of Medicine, New Haven, CT, USA.
Mol Microbiol. 2020 Jun;113(6):1122-1139. doi: 10.1111/mmi.14482. Epub 2020 Feb 21.
The Lyme disease bacterium Borrelia burgdorferi has 7-11 periplasmic flagella (PF) that arise from the cell poles and extend toward the midcell as a flat-ribbon, which is distinct from other bacteria. FlhF, a signal recognition particle (SRP)-like GTPase, has been found to regulate the flagellar number and polarity; however, its role in B. burgdorferi remains unknown. B. burgdorferi has an FlhF homolog (BB0270). Structural and biochemical analyses show that BB0270 has a similar structure and enzymatic activity as its counterparts from other bacteria. Genetics and cryo-electron tomography studies reveal that deletion of BB0270 leads to mutant cells that have less PF (4 ± 2 PF per cell tip) and fail to form a flat-ribbon, indicative of a role of BB0270 in the control of PF number and configuration. Mechanistically, we demonstrate that BB0270 localizes at the cell poles and controls the number and position of PF via regulating the flagellar protein stability and the polar localization of the MS-ring protein FliF. Our study not only provides the detailed characterizations of BB0270 and its profound impacts on flagellar assembly, morphology and motility in B. burgdorferi, but also unveils mechanistic insights into how spirochetes control their unique flagellar patterns.
莱姆病细菌伯氏疏螺旋体有7至11根周质鞭毛（PF），这些鞭毛从细胞两极发出，呈扁平带状向细胞中部延伸，这与其他细菌不同。FlhF是一种信号识别颗粒（SRP）样GTP酶，已被发现可调节鞭毛数量和极性；然而，它在伯氏疏螺旋体中的作用尚不清楚。伯氏疏螺旋体有一个FlhF同源物（BB0270）。结构和生化分析表明，BB0270与其来自其他细菌的对应物具有相似的结构和酶活性。遗传学和冷冻电子断层扫描研究表明，删除BB0270会导致突变细胞的PF减少（每个细胞顶端4±2根PF），且无法形成扁平带状，这表明BB0270在控制PF数量和形态方面发挥作用。从机制上讲，我们证明BB0270定位于细胞两极，并通过调节鞭毛蛋白稳定性和MS环蛋白FliF的极性定位来控制PF的数量和位置。我们的研究不仅详细描述了BB0270及其对伯氏疏螺旋体鞭毛组装、形态和运动性的深远影响，还揭示了螺旋体如何控制其独特鞭毛模式的机制见解。
