Bacteria use vitaminC (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 ofvitaminC and its phosphorylation to L-ascorbate 6-phosphate. Here, we present the crystal structures of vitaminC-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 vitaminC. 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.

Luo P, Yu XZ, Wang WG, Fan SL, Li XC*, Wang JW*. (2015) Crystal structure of a phosphorylation-coupled vitamin C transporter. Nature Structural & Molecular Biology, 22(3):238-241.