Genetic evidence for substrate and periplasmic-binding-protein recognition by the MalF and MalG proteins, cytoplasmic membrane components of the Escherichia coli maltose transport system.
We isolated mutants of Escherichia coli in which the maltose-binding protein (MBP) is no longer required for growth on maltose as the sole source of carbon and energy. These mutants were selected as Mal+ revertants of a strain which carries a deletion of the MBP structural gene, malE. In one class of these mutants, maltose is transported into the cell independently of MBP by the remaining components of the maltose system. The mutations in these strains map in either malF or malG. These genes code for two of the cytoplasmic membrane components of the maltose transport system. In some of the mutants, MBP actually inhibits maltose transport. We demonstrate that these mutants still transport maltose actively and in a stereospecific manner. These results suggest that the malF and malG mutations result in exposure of a substrate recognition site that is usually available only to substrates bound to MBP.
D018528:ATP-Binding Cassette Transporters; D000483:Alleles; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D003090:Coliphages / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029968:Escherichia coli Proteins; D005796:Genes; D005798:Genes, Bacterial; D005838:Genotype; D008320:Maltose / Q000378:metabolism; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins / Q000235:genetics*; D009004:Monosaccharide Transport Proteins; D009154:Mutation; D033902:Periplasmic Binding Proteins; D011995:Recombination, Genetic
D018528:ATP-Binding Cassette Transporters; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; C461619:MalE protein, E coli; C079123:MalG protein, E coli; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; C461599:maltose transport system, E coli; D008320:Maltose