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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.


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Putative membrane topology of stator proteins, PomA/B, MotA and MotB. Amino acid residues marked by a circle in the transmembrane helix of the B subunit are the sites of attention in this study. Abbreviations: VP, Vibrio parahaemolyticus; VC, Vibrio cholera; SWA, Shewanella oneidensis; RSH, Rhodobacter sphaeroides; Pae, Pseudomonas aeruginosa; EC, Escherichia coli.
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f1-5_45: Putative membrane topology of stator proteins, PomA/B, MotA and MotB. Amino acid residues marked by a circle in the transmembrane helix of the B subunit are the sites of attention in this study. Abbreviations: VP, Vibrio parahaemolyticus; VC, Vibrio cholera; SWA, Shewanella oneidensis; RSH, Rhodobacter sphaeroides; Pae, Pseudomonas aeruginosa; EC, Escherichia coli.

Mentions: Blair and coworkers proposed an initial model of MotA4MotB2 (PomA4PomB2) organization8, in which a dimer of MotB transmembrane segments is located at the center of the complex. Transmembrane segments 3 (TM3) and 4 (TM4) of four MotA molecules are arranged in the inner layer around the MotB segments, and TM1 and TM2 are located on the outside. Thus TM3 and TM4 of MotA (PomA) are in close proximity to TM of MotB (PomB) (Figure 1). Only one carboxylic acid residue, Asp32 of MotB and Asp24 of PomB, exists in the predicted transmembrane regions of MotA/B and PomA/B, respectively (Figure 1). Because the D32N mutant of MotB9 and the D24C mutant of PomB10 do not mediate the flagellar motor rotation, those aspartic residues are believed to form a H+ binding site(s) of the MotA/B complex and a Na+ binding site(s) of the PomA/B complex. However, the ion flux pathways from the periplasm to the cytoplasm through these critical aspartate residues are still unclear. The ion flux mechanism of these protein complexes become a focus of great interest, in part because of its importance to the general understanding of the ion flux mechanism in membrane proteins, about which little is known.


Comparative study of the ion flux pathway in stator units of proton- and sodium-driven flagellar motors
Putative membrane topology of stator proteins, PomA/B, MotA and MotB. Amino acid residues marked by a circle in the transmembrane helix of the B subunit are the sites of attention in this study. Abbreviations: VP, Vibrio parahaemolyticus; VC, Vibrio cholera; SWA, Shewanella oneidensis; RSH, Rhodobacter sphaeroides; Pae, Pseudomonas aeruginosa; EC, Escherichia coli.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5036635&req=5

f1-5_45: Putative membrane topology of stator proteins, PomA/B, MotA and MotB. Amino acid residues marked by a circle in the transmembrane helix of the B subunit are the sites of attention in this study. Abbreviations: VP, Vibrio parahaemolyticus; VC, Vibrio cholera; SWA, Shewanella oneidensis; RSH, Rhodobacter sphaeroides; Pae, Pseudomonas aeruginosa; EC, Escherichia coli.
Mentions: Blair and coworkers proposed an initial model of MotA4MotB2 (PomA4PomB2) organization8, in which a dimer of MotB transmembrane segments is located at the center of the complex. Transmembrane segments 3 (TM3) and 4 (TM4) of four MotA molecules are arranged in the inner layer around the MotB segments, and TM1 and TM2 are located on the outside. Thus TM3 and TM4 of MotA (PomA) are in close proximity to TM of MotB (PomB) (Figure 1). Only one carboxylic acid residue, Asp32 of MotB and Asp24 of PomB, exists in the predicted transmembrane regions of MotA/B and PomA/B, respectively (Figure 1). Because the D32N mutant of MotB9 and the D24C mutant of PomB10 do not mediate the flagellar motor rotation, those aspartic residues are believed to form a H+ binding site(s) of the MotA/B complex and a Na+ binding site(s) of the PomA/B complex. However, the ion flux pathways from the periplasm to the cytoplasm through these critical aspartate residues are still unclear. The ion flux mechanism of these protein complexes become a focus of great interest, in part because of its importance to the general understanding of the ion flux mechanism in membrane proteins, about which little is known.

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.


Related in: MedlinePlus