title: Substrate specificities of glycosyltransferases involved in formation of heparin precursor and E. coli K5 capsular polysaccharides.
abstract: The E. coli K5 capsular polysaccharide is composed of 4)GlcpA(beta 1-4)GlcpNAc(alpha 1-disaccharide units. A partially N-deacetylated/N-sulfated heptasaccharide, derived from this polymer and having a nonreducing terminal GlcNAc unit, was used as acceptor for a mastocytoma microsomal GlcA-transferase involved in heparin biosynthesis. An octasaccharide with nonreducing-terminal GlcA similarly served as acceptor for the microsomal GlcNAc-transferase. Analysis of the labeled octa- and nona-saccharides formed by transfer of monosaccharide units from UDP-[14C]GlcA and UDP-[3H]GlcNAc, respectively, showed that both glycosyltransferases could utilize partially N-sulfated acceptors. The GlcA-transferase showed a marked preference for a terminal GlcNAc-GlcA-GlcNSO3-sequence, particularly when this sequence was followed by an additional N-sulfated disaccharide unit. Enzymes catalyzing the same GlcA and GlcNAc transfer reactions were solubilized from E. coli K5 membranes. The K5 capsular polysaccharide, like the heparin/heparan sulfate precursor polysaccharide, thus probably grows by stepwise, alternating addition of the two constituent monosaccharide units, from the corresponding UDP-sugars, to the nonreducing ends of the chains. Moreover, the bacterial glycosyltransferases utilized the same partially N-sulfated oligosaccharide substrates as the mammalian enzymes, and with similar preference for N-sulfate groups in certain positions.
authors.affiliation: Department of Medical and Physiological Chemistry, University of Uppsala, Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Lidholt
authors.forename: M
authors.initials: M
authors.lastname: Fjelstad
authors.forename: K
authors.initials: K
authors.lastname: Jann
authors.forename: U
authors.initials: U
authors.lastname: Lindahl
mesh_terms: D000818:Animals; D016667:Bacterial Capsules; D002240:Carbohydrate Sequence; D004926:Escherichia coli / Q000737:chemistry; D016695:Glycosyltransferases / Q000378:metabolism*; D006493:Heparin / Q000096:biosynthesis*; D012515:Mast-Cell Sarcoma / Q000201:enzymology*; D051379:Mice; D008861:Microsomes / Q000201:enzymology*; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000378:metabolism*; D011135:Polysaccharides, Bacterial / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D009844:Oligosaccharides; D011135:Polysaccharides, Bacterial; C050673:capsular polysaccharide K5; D006493:Heparin; D016695:Glycosyltransferases