A slow-motility phenotype caused by substitutions at residue Asp31 in the PomA channel component of a sodium-driven flagellar motor.
PomA is thought to be a component of the ion channel in the sodium-driven polar-flagellar motor of Vibrio alginolyticus. We have found that some cysteine substitutions in the periplasmic region of PomA result in a slow-motility phenotype, in which swarming and swimming speeds are reduced even in the presence of high concentrations of NaCl. Most of the mutants showed a sodium ion dependence similar to that of the wild type but with significantly reduced motility at all sodium ion concentrations. By contrast, motility of the D31C mutant showed a sharp dependence on NaCl concentration, with a threshold at 38 mM. The motor of the D31C mutant rotates stably, as monitored by laser dark-field microscopy, suggesting that the mutant PomA protein is assembled normally into the motor complex. Mutational studies of Asp31 suggest that, although this residue is not essential for motor rotation, a negative charge at this position contributes to optimal speed and/or efficiency of the motor.
Kojima
S
S
Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan.
Shoji
T
T
Asai
Y
Y
Kawagishi
I
I
Homma
M
M
D000595:Amino Acid Sequence; D001224:Aspartic Acid; D001426:Bacterial Proteins; D005407:Flagella / Q000235:genetics*; D008958:Models, Molecular; D020409:Molecular Motor Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D009068:Movement / Q000502:physiology*; D016297:Mutagenesis, Site-Directed; D010641:Phenotype; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000235:genetics*; D012965:Sodium Chloride / Q000378:metabolism; D014733:Vibrio / Q000502:physiology*
D001426:Bacterial Proteins; D020409:Molecular Motor Proteins; C107540:PomA protein, Vibrio; D015222:Sodium Channels; D001224:Aspartic Acid; D012965:Sodium Chloride; D012964:Sodium