Mutations in the MotA protein of Escherichia coli reveal domains critical for proton conduction.
The MotA protein of Escherichia coli is an essential component of the torque-generating units that drive the flagellar rotary motor. A variety of evidence indicates that MotA is involved in transmembrane proton conduction. We have now mapped a number of MotA mutants, focusing primarily on those previously shown to be dominant. Fifty-six mutations (all dominant), each causing severe or complete impairment of function, were sequenced and found to correspond to 31 different alleles. All except two of these encoded amino acid substitutions clustered in four hydrophobic, presumably membrane-spanning segments, that together make up only one-third of the length of the polypeptide chain. In contrast, eight mutations (5 dominant), each causing only slight impairment of function (slow alleles), were sequenced and found to specify amino acid substitutions in three hydrophilic domains. The clustering of the mutations provides independent support for the suggestion that MotA is a transmembrane proton channel and places significant constraints on models for the molecular mechanism of ion conduction.
Blair
D F
DF
Department of Cellular and Developmental Biology, Harvard University, Cambridge, MA 02138.
Berg
H C
HC
D000483:Alleles; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004252:DNA Mutational Analysis; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D019286:Endopeptidase K; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D005799:Genes, Dominant / Q000235:genetics; D007473:Ion Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D011522:Protons; D012697:Serine Endopeptidases / Q000378:metabolism; D013104:Spheroplasts / Q000378:metabolism; D014764:Viral Proteins
D001426:Bacterial Proteins; D007473:Ion Channels; D008565:Membrane Proteins; C063010:MotA protein, Bacteria; D011522:Protons; D014764:Viral Proteins; C062210:bacteriophage T7 RNA polymerase; D012321:DNA-Directed RNA Polymerases; D012697:Serine Endopeptidases; D019286:Endopeptidase K