title: Lactose permease of Escherichia coli: properties of mutants defective in substrate translocation.
abstract: Mutants of lactose permease of Escherichia coli with amino acid changes (Gly-24----Glu; Gly-24----Arg; Pro-28---Ser; Gly-24, Pro-28----Glu-Ser and Gly-24, Pro-28----Arg-Ser) within a putative membrane-spanning alpha-helix (Phe-Gly-Leu-Phe-Phe-Phe-Phe-Tyr-Phe-Phe-Ile-Met-Gly- Ala-Tyr-Phe-Pro-Phe-Phe-Pro-Ile) are incorporated into the cytoplasmic membrane. The mutant proteins retain the ability to bind galactosides, and the affinity for several substrates is actually increased. However, the rate of active transport is decreased to 0.01% of the wild-type rate in the mutants carrying Arg-24 or Arg-24, Ser-28. Kinetic analysis demonstrates that the two mutants require 10 min to cause occupied binding sites for galactoside and H+ to change their exposure from the periplasm to the cytoplasm as compared to 50 ms in the wild type. The effect is less pronounced when these sites are unoccupied.
authors.forename: P
authors.initials: P
authors.lastname: Overath
authors.forename: U
authors.initials: U
authors.lastname: Weigel
authors.forename: J M
authors.initials: JM
authors.lastname: Neuhaus
authors.forename: J
authors.initials: J
authors.lastname: Soppa
authors.forename: R
authors.initials: R
authors.lastname: Seckler
authors.forename: I
authors.initials: I
authors.lastname: Riede
authors.forename: H
authors.initials: H
authors.lastname: Bocklage
authors.forename: B
authors.initials: B
authors.lastname: Müller-Hill
authors.forename: G
authors.initials: G
authors.lastname: Aichele
authors.forename: J K
authors.initials: JK
authors.lastname: Wright
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport; D004269:DNA, Bacterial / Q000032:analysis; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D005697:Galactosides / Q000378:metabolism; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D009004:Monosaccharide Transport Proteins; D009154:Mutation; D027981:Symporters; D014178:Translocation, Genetic
chemical_list: D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D005697:Galactosides; C050221:LacY protein, E coli; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D027981:Symporters; C021499:lactose permease