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Comparative study of the ion flux pathway in stator units of proton- and sodium-driven flagellar motors

View Article: PubMed Central - PubMed

ABSTRACT

Flagellar motor proteins, MotA/B and PomA/B, are essential for the motility of Escherichia coli and Vibrio alginolyticus, respectively. Those complexes work as a H+ and a Na+ channel, respectively and play important roles in torque generation as the stators of the flagellar motors. Although Asp32 of MotB and Asp24 of PomB are believed to function as ion binding site(s), the ion flux pathway from the periplasm to the cytoplasm is still unclear. Conserved residues, Ala39 of MotB and Cys31 of PomB, are located on the same sides as Asp32 of MotB and Asp24 of PomB, respectively, in a helical wheel diagram. In this study, a series of mutations were introduced into the Ala39 residue of MotB and the Cys31 residue of PomB. The motility of mutant cells were markedly decreased as the volume of the side chain increased. The loss of function due to the MotB(A39V) and PomB(L28A/C31A) mutations was suppressed by mutations of MotA(M206S) and PomA(L183F), respectively, and the increase in the volume caused by the MotB(A39V) mutation was close to the decrease in the volume caused by the MotA(M206S) mutation. These results demonstrate that Ala39 of MotB and Cys31 of PomB form part of the ion flux pathway and pore with Met206 of MotA and Leu183 of PomA in the MotA/B and PomA/B stator units, respectively.

No MeSH data available.


Model of the ion flux pathway. Asp24 of PomB and Asp32 of MotB form Na+ and H+ binding sites, respectively, Cys31(PomB)-Leu183(PomA) and Ala39(MotB)-Met206(MotA) serve as a ion channel wall and a regulator for H+ and Na+ flux, respectively. The ion flux leads to interaction changes and structural change(s) of FliG, and they mediate the flagellar motor rotation.
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f6-5_45: Model of the ion flux pathway. Asp24 of PomB and Asp32 of MotB form Na+ and H+ binding sites, respectively, Cys31(PomB)-Leu183(PomA) and Ala39(MotB)-Met206(MotA) serve as a ion channel wall and a regulator for H+ and Na+ flux, respectively. The ion flux leads to interaction changes and structural change(s) of FliG, and they mediate the flagellar motor rotation.

Mentions: On the basis of our results combined with previous studies, we propose a model of the ion flux pathway through MotA/B and PomA/B ion channels (Figure 6). Asp24 of PomB and Asp32 of MotB form a Na+ and a H+ binding site, respectively. Residues conserved in the Na+-driven flagellar motors include Cys (Cys31 of PomB) and those in the H+-driven ones include Ala (Ala39 of MotB). Those residues are located at the periplasmic side of the membrane spanning domain of each subunit (Figure 1), and are important for ion translocation (Figures 2, 3 and 4). These results support a model in which Cys31 of PomB and Ala39 of MotB face toward the Na+ and H+ flux pathways in the complex, respectively. The loss of function caused by the MotB(A39V) and PomB(L28A/C31A) mutations was suppressed by the MotA(M206S) and PomA(L183F) mutations, respectively, and the increase in the side chain volume caused by MotB(A39V) (50 Å3) was close to the decrease caused by MotA-M206S (72 Å3) (Figure 5), which implies that Met206 of MotA and Leu183 of PomA form the ion channel pore with Ala39 of MotB and Cys31 of PomB, respectively (Figure 6).


Comparative study of the ion flux pathway in stator units of proton- and sodium-driven flagellar motors
Model of the ion flux pathway. Asp24 of PomB and Asp32 of MotB form Na+ and H+ binding sites, respectively, Cys31(PomB)-Leu183(PomA) and Ala39(MotB)-Met206(MotA) serve as a ion channel wall and a regulator for H+ and Na+ flux, respectively. The ion flux leads to interaction changes and structural change(s) of FliG, and they mediate the flagellar motor rotation.
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Related In: Results  -  Collection

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f6-5_45: Model of the ion flux pathway. Asp24 of PomB and Asp32 of MotB form Na+ and H+ binding sites, respectively, Cys31(PomB)-Leu183(PomA) and Ala39(MotB)-Met206(MotA) serve as a ion channel wall and a regulator for H+ and Na+ flux, respectively. The ion flux leads to interaction changes and structural change(s) of FliG, and they mediate the flagellar motor rotation.
Mentions: On the basis of our results combined with previous studies, we propose a model of the ion flux pathway through MotA/B and PomA/B ion channels (Figure 6). Asp24 of PomB and Asp32 of MotB form a Na+ and a H+ binding site, respectively. Residues conserved in the Na+-driven flagellar motors include Cys (Cys31 of PomB) and those in the H+-driven ones include Ala (Ala39 of MotB). Those residues are located at the periplasmic side of the membrane spanning domain of each subunit (Figure 1), and are important for ion translocation (Figures 2, 3 and 4). These results support a model in which Cys31 of PomB and Ala39 of MotB face toward the Na+ and H+ flux pathways in the complex, respectively. The loss of function caused by the MotB(A39V) and PomB(L28A/C31A) mutations was suppressed by the MotA(M206S) and PomA(L183F) mutations, respectively, and the increase in the side chain volume caused by MotB(A39V) (50 Å3) was close to the decrease caused by MotA-M206S (72 Å3) (Figure 5), which implies that Met206 of MotA and Leu183 of PomA form the ion channel pore with Ala39 of MotB and Cys31 of PomB, respectively (Figure 6).

View Article: PubMed Central - PubMed

ABSTRACT

Flagellar motor proteins, MotA/B and PomA/B, are essential for the motility of Escherichia coli and Vibrio alginolyticus, respectively. Those complexes work as a H+ and a Na+ channel, respectively and play important roles in torque generation as the stators of the flagellar motors. Although Asp32 of MotB and Asp24 of PomB are believed to function as ion binding site(s), the ion flux pathway from the periplasm to the cytoplasm is still unclear. Conserved residues, Ala39 of MotB and Cys31 of PomB, are located on the same sides as Asp32 of MotB and Asp24 of PomB, respectively, in a helical wheel diagram. In this study, a series of mutations were introduced into the Ala39 residue of MotB and the Cys31 residue of PomB. The motility of mutant cells were markedly decreased as the volume of the side chain increased. The loss of function due to the MotB(A39V) and PomB(L28A/C31A) mutations was suppressed by mutations of MotA(M206S) and PomA(L183F), respectively, and the increase in the volume caused by the MotB(A39V) mutation was close to the decrease in the volume caused by the MotA(M206S) mutation. These results demonstrate that Ala39 of MotB and Cys31 of PomB form part of the ion flux pathway and pore with Met206 of MotA and Leu183 of PomA in the MotA/B and PomA/B stator units, respectively.

No MeSH data available.