The ascorbate transporter of Escherichia coli

J Bacteriol. 2003 Apr;185(7):2243-50. doi: 10.1128/JB.185.7.2243-2250.2003.


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].

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Anaerobiosis
  • Ascorbic Acid / analogs & derivatives
  • Ascorbic Acid / metabolism*
  • Ascorbic Acid / pharmacology
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Biological Transport, Active
  • Carrier Proteins / drug effects
  • Carrier Proteins / genetics*
  • Carrier Proteins / metabolism*
  • Cell Division / genetics
  • Cyclic AMP Receptor Protein / genetics
  • Cyclic AMP Receptor Protein / metabolism
  • Escherichia coli / drug effects
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Escherichia coli Proteins / chemistry*
  • Escherichia coli Proteins / drug effects
  • Escherichia coli Proteins / genetics*
  • Escherichia coli Proteins / metabolism*
  • Gene Expression Regulation, Bacterial
  • Iron-Sulfur Proteins / genetics
  • Iron-Sulfur Proteins / metabolism
  • Membrane Transport Proteins / chemistry*
  • Membrane Transport Proteins / drug effects
  • Membrane Transport Proteins / genetics*
  • Mutation
  • Phosphoenolpyruvate Sugar Phosphotransferase System / drug effects
  • Phosphoenolpyruvate Sugar Phosphotransferase System / genetics*
  • Phosphoenolpyruvate Sugar Phosphotransferase System / metabolism*
  • Phosphorylation
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism
  • Transcription, Genetic


  • Bacterial Proteins
  • Carrier Proteins
  • Cyclic AMP Receptor Protein
  • Escherichia coli Proteins
  • FNR protein, E coli
  • Iron-Sulfur Proteins
  • Membrane Transport Proteins
  • Repressor Proteins
  • SgaT protein, E coli
  • YifQ protein, E coli
  • ferric uptake regulating proteins, bacterial
  • Phosphoenolpyruvate Sugar Phosphotransferase System
  • SgaA protein, E coli
  • SgaB protein, E coli
  • Ascorbic Acid