title: In vitro characterization of IroB, a pathogen-associated C-glycosyltransferase.
abstract: Pathogenic strains of Escherichia coli and Salmonella enterica modify the tricatecholic siderophore enterobactin (Ent) by glucosylation of three aryl carbon atoms, a process controlled by the iroA locus [Hantke, K., Nicholson, G., Rabsch, W. & Winkelmann, G. (2003) Proc. Natl. Acad. Sci. USA 100, 3677-3682]. Here, we report the purification of the IroB protein and its characterization as the Ent C-glucosyltransferase. IroB transfers glucosyl groups from uridine-5'-diphosphoglucose to C5 of one, two, or three of the 2,3-dihydroxybenzoyl units of Ent to yield monoglucosyl-C-Ent (MGE), diglucosyl-C-Ent (DGE), and triglucosyl-C-Ent (TGE). DGE, also known as salmochelin S4, and macrolactone-opened derivatives have been isolated from the culture broths of S. enterica and uropathogenic E. coli [Bister, B., Bischoff, D., Nicholson, G. J., Valdebenito, M., Schneider, K., Winkelmann, G., Hantke, K. & Sussmuth, R. D. (2004) Biometals 17, 471-481], but MGE and TGE have not been reported previously. IroB has a k(cat) of approximately 10 min(-1) for the first C-glucosylation and is distributive, with sequential conversion and buildup of MGE and then DGE. The C5 to C1' regio-selectivity of the 2,3-dihydroxybenzoyl-glucose linkage at all three rings of TGE suggests a C5 carbanion, para to the C2 phenolate oxygen, as the carbon nucleophile in this novel enzymatic C-glucosylation.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Fischbach
authors.forename: Hening
authors.initials: H
authors.lastname: Lin
authors.forename: David R
authors.initials: DR
authors.lastname: Liu
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Walsh
mesh_terms: D003001:Cloning, Molecular / Q000379:methods; D004758:Enterobactin / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005964:Glucosyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006031:Glycosylation; D016695:Glycosyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D014532:Uridine Diphosphate Glucose / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D004758:Enterobactin; D016695:Glycosyltransferases; D005964:Glucosyltransferases; C497513:IroB protein, E coli; D014532:Uridine Diphosphate Glucose