Crystal structure of a phosphorylation-coupled vitamin C transporter

Nat Struct Mol Biol. 2015 Mar;22(3):238-41. doi: 10.1038/nsmb.2975. Epub 2015 Feb 16.


Bacteria use vitamin C (L-ascorbic acid) as a carbon source under anaerobic conditions. The phosphoenolpyruvate-dependent phosphotransferase system (PTS), comprising a transporter (UlaA), a IIB-like enzyme (UlaB) and a IIA-like enzyme (UlaC), is required for the anaerobic uptake of vitamin C and its phosphorylation to L-ascorbate 6-phosphate. Here, we present the crystal structures of vitamin C-bound UlaA from Escherichia coli in two conformations at 1.65-Å and 2.35-Å resolution. UlaA forms a homodimer and exhibits a new fold. Each UlaA protomer consists of 11 transmembrane segments arranged into a 'V-motif' domain and a 'core' domain. The V motifs form the interface between the two protomers, and the core-domain residues coordinate vitamin C. The alternating access of the substrate from the opposite side of the cell membrane may be achieved through rigid-body rotation of the core relative to the V motif.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ascorbic Acid / chemistry*
  • Ascorbic Acid / metabolism
  • Binding Sites
  • Biological Transport
  • Crystallography, X-Ray
  • Escherichia coli Proteins / chemistry*
  • Escherichia coli Proteins / metabolism
  • Membrane Transport Proteins / chemistry*
  • Membrane Transport Proteins / metabolism
  • Models, Molecular
  • Phosphorylation
  • Protein Structure, Tertiary


  • Escherichia coli Proteins
  • Membrane Transport Proteins
  • SgaT protein, E coli
  • Ascorbic Acid

Associated data

  • PDB/4RP8
  • PDB/4RP9