RESUMEN
Escherichia coli displays O antigens on the outer membrane that play an important role in bacterial interactions with the environment. The O antigens of enterohemorrhagic E. coli O104 and O5 contain a Galß1-3GalNAc disaccharide at the reducing end of the repeating unit. Several other O antigens contain this disaccharide, which is identical to the mammalian O-glycan core 1 or the cancer-associated Thomsen-Friedenreich (TF) antigen. We identified the wbwC genes responsible for the synthesis of the disaccharide in E. coli serotypes O104 and O5. To functionally characterize WbwC, an acceptor substrate analog, GalNAcα-diphosphate-phenylundecyl, was synthesized. WbwC reaction products were isolated by high-pressure liquid chromatography and analyzed by mass spectrometry, nuclear magnetic resonance, galactosidase and O-glycanase digestion, and anti-TF antibody. The results clearly showed that the Galß1-3GalNAcα linkage was synthesized, confirming WbwCECO104 and WbwCECO5 as UDP-Gal:GalNAcα-diphosphate-lipid ß1,3-Gal-transferases. Sequence analysis revealed a conserved DxDD motif, and mutagenesis showed the importance of these Asp residues in catalysis. The purified enzymes require divalent cations (Mn(2+)) for activity and are specific for UDP-Gal and GalNAc-diphosphate lipid substrates. WbwC was inhibited by bis-imidazolium salts having aliphatic chains of 18 to 22 carbons. This work will help to elucidate mechanisms of polysaccharide synthesis in pathogenic bacteria and provide technology for vaccine synthesis.
Asunto(s)
Escherichia coli Enterohemorrágica/enzimología , Proteínas de Escherichia coli/metabolismo , Galactosiltransferasas/metabolismo , Secuencia de Aminoácidos , Escherichia coli Enterohemorrágica/clasificación , Escherichia coli Enterohemorrágica/genética , Escherichia coli Enterohemorrágica/metabolismo , Proteínas de Escherichia coli/genética , Galactosiltransferasas/genética , Regulación Bacteriana de la Expresión Génica/fisiología , Regulación Enzimológica de la Expresión Génica , SerotipificaciónRESUMEN
The assembly of the repeating units of O-antigens in Gram negative bacteria is catalyzed by specific glycosyltransferases. Previously we used GlcNAc/GalNAcα-diphosphate-phenoxyundecyl as natural acceptor substrate analogs in assays of the transfer of radioactive sugars by bacterial glycosyltransferases. In order to develop new, fluorescence based assays we have synthesized a fluorescent acceptor P¹-[11-(anthracen-9-ylmethoxy)undecyl]-P²-(2-acetamido-2-deoxy-α-D-galactopyranosyl) diphosphate and have shown that the compound was an excellent acceptor for glucosyltransferase WbdN from Escherichia coli (E. coli) O157 and for galactosyltransferase WbwC from E. coli O5. This is the first report of the Gal-transferase activity of the wbwC gene product of E.coli O5. The presence of the fluorescent label in the acceptor molecule allows the detection of glycosyltransferase reaction products with high sensitivity, eliminating the need for radioactive nucleotide sugars.