Functional role of a conserved aspartic acid residue in the motor of the Na-driven flagellum from Vibrio cholerae |
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Authors: | Thomas Vorburger Urs Ziegler Julia Steuber |
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Affiliation: | a Biochemisches Institut, Universität Zürich, 8057 Zürich, Switzerland b Zentrum für Mikroskopie und Bildanalyse, Universität Zürich, 8057 Zürich, Switzerland c Gene Analytics, Bahnhofstrasse 16, 86486 Bonstetten, Germany |
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Abstract: | The flagellar motor consists of a rotor and a stator and couples the flux of cations (H+ or Na+) to the generation of the torque necessary to drive flagellum rotation. The inner membrane proteins PomA and PomB are stator components of the Na+-driven flagellar motor from Vibrio cholerae. Affinity-tagged variants of PomA and PomB were co-expressed in trans in the non-motile V. cholerae pomAB deletion strain to study the role of the conserved D23 in the transmembrane helix of PomB. At pH 9, the D23E variant restored motility to 100% of that observed with wild type PomB, whereas the D23N variant resulted in a non-motile phenotype, indicating that a carboxylic group at position 23 in PomB is important for flagellum rotation. Motility tests at decreasing pH revealed a pronounced decline of flagellar function with a motor complex containing the PomB-D23E variant. It is suggested that the protonation state of the glutamate residue at position 23 determines the performance of the flagellar motor by altering the affinity of Na+ to PomB. The conserved aspartate residue in the transmembrane helix of PomB and its H+-dependent homologs might act as a ligand for the coupling cation in the flagellar motor. |
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Keywords: | Flagellar motor Motility PomB Sodium motive force Vibrio cholerae |
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