Hook John C, Blagotinsek Vitan, Pané-Farré Jan, Mrusek Devid, Altegoer Florian, Dornes Anita, Schwan Meike, Schier Lukas, Thormann Kai M, Bange Gert
Department of Microbiology and Molecular Biology, Justus-Liebig-Universität, Giessen, Germany.
SYNMIKRO Research Center, Department of Chemistry, Philipps-University Marburg, Marburg, Germany.
Front Microbiol. 2020 Dec 15;11:564161. doi: 10.3389/fmicb.2020.564161. eCollection 2020.
Flagella are bacterial organelles of locomotion. Their biogenesis is highly coordinated in time and space and relies on a specialized flagellar type III secretion system (fT3SS) required for the assembly of the extracellular hook, rod, and filament parts of this complex motor device. The fT3SS protein FlhB switches secretion substrate specificity once the growing hook reaches its determined length. Here we present the crystal structure of the cytoplasmic domain of the transmembrane protein FlhB. The structure visualizes a so-far unseen proline-rich region (PRR) at the very C-terminus of the protein. Strains lacking the PRR show a decrease in flagellation as determined by hook- and filament staining, indicating a role of the PRR during assembly of the hook and filament structures. Phylogenetic analysis shows that the PRR is a primary feature of FlhB proteins of flagellated beta- and gamma-proteobacteria. Taken together, our study adds another layer of complexity and organismic diversity to the process of flagella biogenesis.
鞭毛是细菌的运动细胞器。它们的生物合成在时间和空间上高度协调，并依赖于一种特殊的鞭毛III型分泌系统（fT3SS），该系统是组装这种复杂运动装置的细胞外钩、杆和丝状体部分所必需的。一旦生长中的钩达到其确定的长度，fT3SS蛋白FlhB就会切换分泌底物特异性。在这里，我们展示了跨膜蛋白FlhB细胞质结构域的晶体结构。该结构显示了该蛋白C末端一个迄今为止未见的富含脯氨酸的区域（PRR）。通过钩和丝状体染色确定，缺乏PRR的菌株鞭毛形成减少，表明PRR在钩和丝状体结构组装过程中发挥作用。系统发育分析表明，PRR是有鞭毛的β-和γ-变形杆菌FlhB蛋白的一个主要特征。综上所述，我们的研究为鞭毛生物合成过程增加了另一层复杂性和生物多样性。
