Publications

• Bioinformatic analyses of the bacterial L-ascorbate phosphotransferase system permease family.

  Hvorup R., Chang A.B., Saier M.H. Jr.

  The tripartite L-ascorbate permease of Escherichia coli is the first functionally characterized member of a large family of enzyme II complexes (SgaTBA, encoding enzymes IIC, IIB and IIA) of the bacterial phosphotransferase system (PTS). We here report bioinformatic analyses of these proteins. For ... >> More

  The tripartite L-ascorbate permease of Escherichia coli is the first functionally characterized member of a large family of enzyme II complexes (SgaTBA, encoding enzymes IIC, IIB and IIA) of the bacterial phosphotransferase system (PTS). We here report bioinformatic analyses of these proteins. Forty-five homologous systems from a wide variety of bacteria were identified, but no homologues were found in archaea or eukaryotes. These systems fell into five structural types: (1) IIC, IIB and IIA are encoded by distinct genes; (2) IIC and IIB are encoded by distinct genes, but the IIA-encoding gene is absent; (3) IIC and IIB are encoded by a fused gene, but IIA is a distinct gene product; (4) IIA and IIB are fused, but IIC is encoded by a distinct gene, and (5) IIC and IIB are encoded by distinct genes, but IIA is fused to a transcriptional regulator. Phylogenetic analyses revealed that gene fusion/splicing events have occurred repeatedly during the evolutionary divergence of family members, although no evidence for shuffling of constituents between systems was obtained. The SgaTBA family proved to be distantly related to the GatCBA family of PTS permeases, and this family was also analyzed. In contrast to the SgaTBA family, no gene splicing/fusion has occurred during the evolutionary divergence of GatCBA family members as each domain is always encoded by a distinct gene. However, GatC homologues were identified in organisms that lack other PTS proteins, suggesting a transport mechanism not coupled to substrate phosphorylation. Topological analyses suggest that in contrast to all other PTS permeases, IIC proteins of the Sga and Gat families exhibit 12 transmembrane alpha-helical segments and are distantly related to secondary carriers. Like many secondary carriers, GatC (IIC) homologues could be shown to have arisen by an ancient intragenic duplication event. These results suggest that the Sga and Gat families of PTS permeases comprise a small superfamily in which the transmembrane IIC domains evolved independently of all other known PTS permeases. << Less

  J Mol Microbiol Biotechnol 6:191-205(2003) [PubMed] [EuropePMC]

• The ascorbate transporter of Escherichia coli.

  Zhang Z., Aboulwafa M., Smith M.H., Saier M.H. Jr.

  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 pro ... >> More

  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]. << Less

  J. Bacteriol. 185:2243-2250(2003) [PubMed] [EuropePMC]

• Crystal structure of a phosphorylation-coupled vitamin C transporter.

  Luo P., Yu X., Wang W., Fan S., Li X., Wang J.

  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 i ... >> More

  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. << Less

  Nat. Struct. Mol. Biol. 22:238-241(2015) [PubMed] [EuropePMC]