Pourjaberi Seyedeh Noorolhoda Shajari, Terahara Naoya, Namba Keiichi, Minamino Tohru
Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan.
RIKEN, Quantitative Biology Center, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan.
Mol Microbiol. 2017 Nov;106(4):646-658. doi: 10.1111/mmi.13843. Epub 2017 Sep 29.
The proton-driven flagellar motor of Salmonella enterica can accommodate a dozen MotA/B stators in a load-dependent manner. The C-terminal periplasmic domain of MotB acts as a structural switch to regulate the number of active stators in the motor in response to load change. The cytoplasmic loop termed MotA is responsible for the interaction with a rotor protein, FliG. Here, to test if MotA is responsible for stator assembly around the rotor in a load-dependent manner, we analyzed the effect of MotA mutations, M76V, L78W, Y83C, Y83H, I126F, R131L, A145E and E155K, on motor performance over a wide range of external load. All these MotA mutations reduced the maximum speed of the motor near zero load, suggesting that they reduce the rate of conformational dynamics of MotA coupled with proton translocation through the MotA/B proton channel. Dissociation of the stators from the rotor by decrease in the load was facilitated by the M76V, Y83H and A145E mutations compared to the wild-type motor. The E155K mutation reduced the number of active stators in the motor from 10 to 6 under extremely high load. We propose that MotA is responsible for load-dependent assembly and disassembly dynamics of the MotA/B stator units.
肠炎沙门氏菌的质子驱动鞭毛马达能够以负载依赖的方式容纳十二个MotA/B定子。MotB的C端周质结构域作为一个结构开关，可根据负载变化调节马达中活性定子的数量。被称为MotA的胞质环负责与转子蛋白FliG相互作用。在此，为了测试MotA是否以负载依赖的方式负责转子周围定子的组装，我们分析了MotA突变体M76V、L78W、Y83C、Y83H、I126F、R131L、A145E和E155K在广泛的外部负载范围内对马达性能的影响。所有这些MotA突变都降低了接近零负载时马达的最大速度，这表明它们降低了MotA的构象动力学速率以及质子通过MotA/B质子通道的转运速率。与野生型马达相比，M76V、Y83H和A145E突变促进了负载降低时定子与转子的解离。在极高负载下，E155K突变将马达中活性定子的数量从10个减少到6个。我们认为MotA负责MotA/B定子单元的负载依赖组装和解离动力学。
