Transport properties of Asp-51-->Glu and Asp-120-->Glu mutants of the melibiose carrier of Escherichia coli.
Asp-51-->Glu and Asp-120-->Glu mutants of the melibiose carrier of Escherichia coli were investigated for their cation/sugar cotransport properties. The carrier containing Glu-51 showed proton/melibiose cotransport but was extremely defective in Na+ or Li+ stimulation of sugar accumulation. On the other hand, the carrier containing Glu-120 had lost the ability to couple protons with melibiose uptake while retaining considerable Na+ or Li+ cotransport with melibiose (40-fold accumulation versus 90-fold for the wild type in the presence of Na+). It is concluded that both Asp-51 and Asp-120 are important for cation recognition.
Wilson
D M
DM
Department of Cell Biology, Harvard Medical School, Boston, MA 02115.
Wilson
T H
TH
D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D008094:Lithium / Q000378:metabolism; D008553:Melibiose / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D012964:Sodium / Q000378:metabolism
D002352:Carrier Proteins; D008553:Melibiose; D008094:Lithium; D012964:Sodium