The ascorbate transporter of Escherichia coli.
The sgaTBA genes of Escherichia coli encode a putative 12-transmembrane alpha-helical segment (12 TMS) transporter, an enzyme IIB-like protein and an enzyme IIA-like protein of the phosphotransferase system (PTS), respectively. We show that all three proteins as well as the energy-coupling PTS proteins, enzyme I and HPr, are required for the anaerobic utilization and uptake of L-ascorbate in vivo and its phosphoenolpyruvate-dependent phosphorylation in vitro. The transporter exhibits an apparent K(m) for L-ascorbate of 9 micro M and is highly specific. The sgaTBA genes are regulated at the transcriptional level by the yjfQ gene product, as well as by Crp and Fnr. The yjfR gene product is essential for L-ascorbate utilization and probably encodes a cytoplasmic L-ascorbate 6-phosphate lactonase. We conclude that SgaT represents a novel prototypical enzyme IIC that functions with SgaA and SgaB to allow phosphoryl transfer from HPr(his-P) to L-ascorbate via the phosphoryl transfer pathway: [pathway: see text].
Zhang
Zhongge
Z
Division of Biological Sciences, University of California at San Diego, La Jolla, California 92093-0116, USA.
Aboulwafa
Mohammad
M
Smith
Meghan H
MH
Saier
Milton H
MH
D000693:Anaerobiosis; D001205:Ascorbic Acid / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D002455:Cell Division / Q000235:genetics; D002373:Cyclic AMP Receptor Protein / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D007506:Iron-Sulfur Proteins / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics*; D009154:Mutation; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D010766:Phosphorylation; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D002352:Carrier Proteins; D002373:Cyclic AMP Receptor Protein; D029968:Escherichia coli Proteins; C060704:FNR protein, E coli; D007506:Iron-Sulfur Proteins; D026901:Membrane Transport Proteins; D012097:Repressor Proteins; C473320:SgaT protein, E coli; C467899:YifQ protein, E coli; C068477:ferric uptake regulating proteins, bacterial; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C473322:SgaA protein, E coli; C473321:SgaB protein, E coli; D001205:Ascorbic Acid