Isolation and characterization of a mutation that alters the substrate specificity of the Escherichia coli glucose permease

We isolated 10 mannitol-positive mutants from a mannitol-negative Escherichia coli strain. These mutations mapped within ptsG, encoding the glucose permease (EII(Glc)), and resulted in a G-320-to-V substitution that allows EII(Glc) to transport mannitol. Gly-320 lies within a putative transmembrane helix of EII(Glc) that may be involved in substrate recognition.