PMID:1310984
| Citation |
Buhr, A, Daniels, GA and Erni, B (1992) The glucose transporter of Escherichia coli. Mutants with impaired translocation activity that retain phosphorylation activity. J. Biol. Chem. 267:3847-51 |
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| Abstract |
The glucose transporter of the bacterial phosphotransferase system couples translocation with phosphorylation of the substrate in a 1:1 stoichiometry. It is a complex consisting of a transmembrane subunit (IIGlc) and a hydrophilic subunit (IIIGlc). Both subunits are transiently phosphorylated. IIIGlc is phosphorylated at a histidyl residue by the cytoplasmic phosphoryl carrier protein phospho-heat-stable phosphoryl carrier protein; IIGlc is phosphorylated at a cysteinyl residue by phospho-IIIGlc. The IIGlc subunit consists of two domains. The N-terminal hydrophobic domain is presumed to span the membrane several times; the C-terminal cytoplasmic domain includes the phosphorylation site. IIGlc phosphorylates glucose and methyl-alpha-D-glucopyranoside in transit across the inner membrane but can also phosphorylate intracellular glucose. Ten mutants resistant against extracellular toxic methyl-alpha-D-glucopyranoside yet capable of phosphorylating intracellular glucose were isolated. Strong impairment of transport activity in these mutants was accompanied by only a slight decrease of phosphorylation activity. Amino acid substitutions occurred at six sites that are clustered in three presumably hydrophilic loops in the transmembrane domain of IIGlc: M17T, M17I, G149S, K150E, S157F, H339Y, and D343G. We presume that the three polypeptide segments are directly involved in sugar translocation and/or binding but are of little importance for phosphorylation activity, folding, and membrane localization of IIGlc. |
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| Keywords |
Amino Acid Sequence; DNA, Bacterial/genetics; Escherichia coli/enzymology; Escherichia coli/metabolism; Glucose/metabolism; Methylglucosides/metabolism; Molecular Sequence Data; Monosaccharide Transport Proteins/genetics; Monosaccharide Transport Proteins/metabolism; Mutation; Phosphorylation; Phosphotransferases/metabolism; Plasmids; Sequence Homology, Nucleic Acid |
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