Hiraoka Koichi D, Morimoto Yusuke V, Inoue Yumi, Fujii Takashi, Miyata Tomoko, Makino Fumiaki, Minamino Tohru, Namba Keiichi
Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan.
Riken Quantitative Biology Center, 1-3 Yamadoaka, Suita, Osaka 565-0871, Japan.
Sci Rep. 2017 Apr 21;7:46723. doi: 10.1038/srep46723.
The bacterial flagellar hook connects the helical flagellar filament to the rotary motor at its base. Bending flexibility of the hook allows the helical filaments to form a bundle behind the cell body to produce thrust for bacterial motility. The hook protein FlgE shows considerable sequence and structural similarities to the distal rod protein FlgG; however, the hook is supercoiled and flexible as a universal joint whereas the rod is straight and rigid as a drive shaft. A short FlgG specific sequence (GSS) has been postulated to confer the rigidity on the FlgG rod, and insertion of GSS at the position between Phe-42 and Ala-43 of FlgE actually made the hook straight. However, it remains unclear whether inserted GSS confers the rigidity as well. Here, we provide evidence that insertion of GSS makes the hook much more rigid. The GSS insertion inhibited flagellar bundle formation behind the cell body, thereby reducing motility. This indicates that the GSS insertion markedly reduced the bending flexibility of the hook. Therefore, we propose that the inserted GSS makes axial packing interactions of FlgE subunits much tighter in the hook to suppress axial compression and extension of the protofilaments required for bending flexibility.
细菌鞭毛钩将螺旋状的鞭毛丝与其基部的旋转马达相连。钩的弯曲柔韧性使螺旋状丝在细胞体后方形成一束，从而为细菌运动产生推力。钩蛋白FlgE与远端杆蛋白FlgG在序列和结构上有相当大的相似性；然而，钩呈超螺旋状且作为万向节具有柔韧性，而杆则像驱动轴一样笔直且刚性。一个短的FlgG特异性序列（GSS）被假定赋予FlgG杆刚性，并且在FlgE的苯丙氨酸 - 42和丙氨酸 - 43之间的位置插入GSS实际上使钩变直。然而，插入的GSS是否也赋予刚性仍不清楚。在这里，我们提供证据表明插入GSS使钩更具刚性。GSS插入抑制了细胞体后方鞭毛束的形成，从而降低了运动性。这表明GSS插入显著降低了钩的弯曲柔韧性。因此，我们提出插入的GSS使钩中FlgE亚基的轴向堆积相互作用更加紧密，以抑制弯曲柔韧性所需的原丝轴向压缩和伸展。
