Lactose permease of Escherichia coli catalyzes active β-galactoside transport in a gram-positive bacterium

The following several lines of evidence demonstrate that lactose permease (LacY) of Escherichia coli is assembled into the cytoplasmic membrane of gram-positive Corynebacterium glutamicum, expressing the lacY gene, as a functional carrier protein. (i) LacY was detected immunologically in the cytoplasmic membrane fraction of the heterologous host. (ii) Recombinant C. glutamicum cells bearing the lacY gene displayed an increased influx of o- nitrophenyl-β-D-galactopyranoside, which was inhibited by N-ethylmaleimide. (iii) Washed cells were capable of accumulating methyl-β-D-thiogalactoside about 60-fold. (iv) The uptake of methyl-β-D-thiogalactoside was energy dependent and could be inhibited by the addition of 10 μM carbonyl cyanide- m-chlorophenylhydrazone. LacY of E. coli was active in the recombinant C. glutamicum cells despite the different membrane lipid compositions of these organisms.