title: Role of cysteine residues in the lac permease of Escherichia coli.
abstract: Oligonucleotide-directed, site-specific mutagenesis has been utilized to replace cysteine residues 117, 333, or 353 and 355 with serine in the lac permease of Escherichia coli. Replacement of Cys-117 or Cys-333 has no significant effect on permease activity, while permease with serine residues in place of Cys-353 and Cys-355 has about 50% of wild-type permease activity. The results provide a clear demonstration that cysteine residues at positions 117, 333, 353, and 355 are not obligatory for lactose/H+ symport. When considered in conjunction with previous findings, the results indicate that, of the eight cysteine residues in the lac permease, only Cys-154 is important for lactose transport. As discussed, the conclusion has important implications for the hypothesis that sulfhydryl-disulfide interconversion plays an important role in the symport mechanism.
mesh_terms: D003545:Cysteine; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins; D005838:Genotype; D007700:Kinetics; D007785:Lactose / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins; D009154:Mutation; D010957:Plasmids; D027981:Symporters
chemical_list: D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D027981:Symporters; C021499:lactose permease; D007785:Lactose; D003545:Cysteine