The maximum number of torque-generating units in the flagellar motor of Escherichia coli is at least 11
The maximum number of torque-generating units in the flagellar motor of Escherichia coli is at least 11
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DOI：
10.1073/pnas.0509932103
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发表时间：
2006-05-23
影响因子：
11.1
通讯作者：
Berry, Richard M.
中科院分区：
文献类型：
--
作者：
Reid, Stuart W.;Leake, Mark C.;Berry, Richard M.
细菌鞭毛基部的旋转马达中，扭矩是由锚定在肽聚糖细胞壁上的离子转运定子单元产生的。在质子驱动的马达中，定子单元由MotA和MotB蛋白质组成，而在钠驱动的马达中则由PomA和PomB组成。缺乏功能性定子蛋白质的大肠杆菌菌株所产生的鞭毛不旋转，诱导缺失蛋白质的表达会使马达旋转以离散的速度增量恢复，这一过程被称为“复活”。早期的研究表明最多有八个单元。基于对受损马达的修复，近期有迹象表明野生型（WT）马达可能包含多于八个单元，但结论并不确定。在此我们确凿地证明，一个马达中单元的最大数量至少为11个。通过对附着在鞭毛上的1微米聚苯乙烯珠子进行后焦平面干涉测量，我们在大肠杆菌中观察到，在使用三种不同组合的定子蛋白质进行复活过程中，至少有11个不同的速度增量。单个单元和完全诱导的马达所产生的平均扭矩低于先前的估计值。单元数量多时的速度增量比单元数量少时要小，这表明完全诱导的马达中的所有单元并非完全相同。
Torque is generated in the rotary motor at the base of the bacterial flagellum by ion translocating stator units anchored to the peptidoglycan cell wall. Stator units are composed of the proteins MotA and MotB in proton-driven motors, and they are composed of PomA and PomB in sodium-driven motors. Strains of Escherichia coli lacking functional stator proteins produce flagella that do not rotate, and induced expression of the missing proteins leads to restoration of motor rotation in discrete speed increments, a process known as "resurrection." Early work suggested a maximum of eight units. More recent indications that WT motors may contain more than eight units, based on recovery of disrupted motors, are inconclusive. Here we demonstrate conclusively that the maximum number of units in a motor is at least 11. Using back-focal-plane interferometry of 1-mu m polystyrene beads attached to flagella, we observed at least 11 distinct speed increments during resurrection with three different combinations of stator proteins in E. coli. The average torques generated by a single unit and a fully induced motor were lower than previous estimates. Speed increments at high numbers of units are smaller than those at low numbers, indicating that not all units in a fully induced motor are equivalent.