title: X-ray crystal structure of rabbit N-acetylglucosaminyltransferase I: catalytic mechanism and a new protein superfamily.
abstract: N:-acetylglucosaminyltransferase I (GnT I) serves as the gateway from oligomannose to hybrid and complex N:-glycans and plays a critical role in mammalian development and possibly all metazoans. We have determined the X-ray crystal structure of the catalytic fragment of GnT I in the absence and presence of bound UDP-GlcNAc/Mn(2+) at 1.5 and 1.8 A resolution, respectively. The structures identify residues critical for substrate binding and catalysis and provide evidence for similarity, at the mechanistic level, to the deglycosylation step of retaining beta-glycosidases. The structuring of a 13 residue loop, resulting from UDP-GlcNAc/Mn(2+) binding, provides an explanation for the ordered sequential 'Bi Bi' kinetics shown by GnT I. Analysis reveals a domain shared with Bacillus subtilis glycosyltransferase SpsA, bovine beta-1,4-galactosyl transferase 1 and Escherichia coli N:-acetylglucosamine-1-phosphate uridyltransferase. The low sequence identity, conserved fold and related functional features shown by this domain define a superfamily whose members probably share a common ancestor. Sequence analysis and protein threading show that the domain is represented in proteins from several glycosyltransferase families.
authors.affiliation: Department of Medical Genetics and Microbiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
authors.forename: U M
authors.initials: UM
authors.lastname: Unligil
authors.forename: S
authors.initials: S
authors.lastname: Zhou
authors.forename: S
authors.initials: S
authors.lastname: Yuwaraj
authors.forename: M
authors.initials: M
authors.lastname: Sarkar
authors.forename: H
authors.initials: H
authors.lastname: Schachter
authors.forename: J M
authors.initials: JM
authors.lastname: Rini
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D019295:Computational Biology; D018360:Crystallography, X-Ray; D019143:Evolution, Molecular; D006031:Glycosylation; D006860:Hydrogen Bonding; D007700:Kinetics; D008345:Manganese / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017351:N-Acetylglucosaminyltransferases / Q000737:chemistry* / Q000378:metabolism*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011817:Rabbits; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D014537:Uridine Diphosphate N-Acetylglucosamine / Q000378:metabolism
chemical_list: D011994:Recombinant Proteins; D008345:Manganese; D014537:Uridine Diphosphate N-Acetylglucosamine; D017351:N-Acetylglucosaminyltransferases; C024850:alpha-1,3-mannosyl-glycoprotein beta-1,2-N-acetylglucosaminyltransferase I