Institute of Microbiology, University of Hohenheim (Stuttgart), Stuttgart, Germany.
J Bacteriol. 2013 Nov;195(21):4888-99. doi: 10.1128/JB.00353-13. Epub 2013 Aug 23.
Vibrio cholerae is motile by its polar flagellum, which is driven by a Na(+)-conducting motor. The stators of the motor, composed of four PomA and two PomB subunits, provide access for Na(+) to the torque-generating unit of the motor. To characterize the Na(+) pathway formed by the PomAB complex, we studied the influence of chloride salts (chaotropic, Na(+), and K(+)) and pH on the motility of V. cholerae. Motility decreased at elevated pH but increased if a chaotropic chloride salt was added, which rules out a direct Na(+) and H(+) competition in the process of binding to the conserved PomB D23 residue. Cells expressing the PomB S26A/T or D42N variants lost motility at low Na(+) concentrations but regained motility in the presence of 170 mM chloride. Both PomA and PomB were modified by N,N'-dicyclohexylcarbodiimide (DCCD), indicating the presence of protonated carboxyl groups in the hydrophobic regions of the two proteins. Na(+) did not protect PomA and PomB from this modification. Our study shows that both osmolality and pH have an influence on the function of the flagellum from V. cholerae. We propose that D23, S26, and D42 of PomB are part of an ion-conducting pathway formed by the PomAB stator complex.
霍乱弧菌通过其极性鞭毛运动，该鞭毛由一个 Na(+)传导马达驱动。马达的定子由四个 PomA 和两个 PomB 亚基组成，为 Na(+)进入马达的扭矩产生单元提供通道。为了表征 PomAB 复合物形成的 Na(+)途径，我们研究了氯化物盐（离液盐、Na(+)和 K(+)）和 pH 值对霍乱弧菌运动性的影响。运动性在 pH 值升高时降低，但如果添加离液盐氯化物，则会增加，这排除了在与保守的 PomB D23 残基结合过程中 Na(+)和 H(+)的直接竞争。表达 PomB S26A/T 或 D42N 变体的细胞在低 Na(+)浓度下失去运动性，但在存在 170 mM 氯化物的情况下恢复运动性。PomA 和 PomB 都被 N,N'-二环己基碳二亚胺 (DCCD) 修饰，表明两种蛋白质的疏水区存在质子化的羧基。Na(+)不能保护 PomA 和 PomB 免受这种修饰。我们的研究表明渗透压和 pH 值都对霍乱弧菌鞭毛的功能有影响。我们提出 PomB 的 D23、S26 和 D42 是由 PomAB 定子复合物形成的离子传导途径的一部分。
