title: Functional characterization and membrane topology of Escherichia coli WecA, a sugar-phosphate transferase initiating the biosynthesis of enterobacterial common antigen and O-antigen lipopolysaccharide.
abstract: WecA is an integral membrane protein that initiates the biosynthesis of enterobacterial common antigen and O-antigen lipopolysaccharide (LPS) by catalyzing the transfer of N-acetylglucosamine (GlcNAc)-1-phosphate onto undecaprenyl phosphate (Und-P) to form Und-P-P-GlcNAc. WecA belongs to a large family of eukaryotic and prokaryotic prenyl sugar transferases. Conserved aspartic acids in putative cytoplasmic loops 2 (Asp90 and Asp91) and 3 (Asp156 and Asp159) were targeted for replacement mutagenesis with either glutamic acid or asparagine. We examined the ability of each mutant protein to complement O-antigen LPS synthesis in a wecA-deficient strain and also determined the steady-state kinetic parameters of the mutant proteins in an in vitro transfer assay. Apparent K(m) and V(max) values for UDP-GlcNAc, Mg(2+), and Mn(2+) suggest that Asp156 is required for catalysis, while Asp91 appears to interact preferentially with Mg(2+), possibly playing a role in orienting the substrates. Topological analysis using the substituted cysteine accessibility method demonstrated the cytosolic location of Asp90, Asp91, and Asp156 and provided a more refined overall topological map of WecA. Also, we show that cells expressing a WecA derivative C terminally fused with the green fluorescent protein exhibited a punctate distribution of fluorescence on the bacterial surface, suggesting that WecA localizes to discrete regions in the bacterial plasma membrane.
authors.affiliation: Department of Microbiology and Immunology, University of Western Ontario, London, ON N6A 5C1, Canada.
authors.forename: Jason
authors.initials: J
authors.lastname: Lehrer
authors.forename: Karen A
authors.initials: KA
authors.lastname: Vigeant
authors.forename: Laura D
authors.initials: LD
authors.lastname: Tatar
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Valvano
mesh_terms: D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000201:enzymology; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019081:O Antigens / Q000096:biosynthesis*; D010957:Plasmids; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D014166:Transferases / Q000737:chemistry / Q000378:metabolism*; D017855:Transferases (Other Substituted Phosphate Groups) / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D019081:O Antigens; D011994:Recombinant Proteins; D014166:Transferases; D017855:Transferases (Other Substituted Phosphate Groups); C083617:wecA protein, E coli