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首页> 外文期刊>Journal of bacteriology >Function of Protonatable Residues in the Flagellar Motor of Escherichia coli: a Critical Role for Asp 32 of MotB
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Function of Protonatable Residues in the Flagellar Motor of Escherichia coli: a Critical Role for Asp 32 of MotB

机译：质子化残留物在大肠杆菌鞭毛马达中的功能：MotB的Asp 32的关键作用。

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摘要

Rotation of the bacterial flagellar motor is powered by a transmembrane gradient of protons or, in some species, sodium ions. The molecular mechanism of coupling between ion flow and motor rotation is not understood. The proteins most closely involved in motor rotation are MotA, MotB, and FliG. MotA and MotB are transmembrane proteins that function in transmembrane proton conduction and that are believed to form the stator. FliG is a soluble protein located on the cytoplasmic face of the rotor. Two other proteins, FliM and FliN, are known to bind to FliG and have also been suggested to be involved to some extent in torque generation. Proton (or sodium)-binding sites in the motor are likely to be important to its function and might be formed from the side chains of acidic residues. To investigate the role of acidic residues in the function of the flagellar motor, we mutated each of the conserved acidic residues in the five proteins that have been suggested to be involved in torque generation and measured the effects on motility. None of the conserved acidic residues of MotA, FliG, FliM, or FliN proved essential for torque generation. An acidic residue at position 32 of MotB did prove essential. Of 15 different substitutions studied at this position, only the conservative-replacement D32E mutant retained any function. Previous studies, together with additional data presented here, indicate that the proteins involved in motor rotation do not contain any conserved basic residues that are critical for motor rotation per se. We propose that Asp 32 of MotB functions as a proton-binding site in the bacterial flagellar motor and that no other conserved, protonatable residues function in this capacity.
机译：细菌鞭毛马达的旋转由质子或在某些物种中的钠离子的跨膜梯度提供动力。离子流与电机旋转之间耦合的分子机理尚不清楚。与运动旋转最密切相关的蛋白质是MotA，MotB和FliG。 MotA和MotB是在跨膜质子传导中起作用的跨膜蛋白，被认为可以形成定子。 FliG是位于转子细胞质面上的可溶性蛋白。已知其他两种蛋白质FliM和FliN与FliG结合，并且还被认为在一定程度上参与了扭矩的产生。马达中的质子（或钠）结合位点可能对其功能很重要，并且可能是由酸性残基的侧链形成的。为了研究酸性残基在鞭毛运动功能中的作用，我们突变了五个蛋白质中的每个保守的酸性残基，这些蛋白质被认为与扭矩产生有关，并测量了对运动性的影响。 MotA，FliG，FliM或FliN的保守酸性残基均未证明对产生扭矩至关重要。事实证明，MotB第32位的酸性残基至关重要。在该位置研究的15个不同取代中，只有保守置换D32E突变体保留了任何功能。先前的研究以及此处提供的其他数据表明，与电机旋转有关的蛋白质不含任何保守的基本残基，这些残基对于电机本身的旋转至关重要。我们提出MotB的Asp 32作为细菌鞭毛马达中的质子结合位点，并且没有其他保守的可质子化残基以这种能力起作用。

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