title: Cloning and characterization of mammalian UDP-glucose glycoprotein: glucosyltransferase and the development of a specific substrate for this enzyme.
abstract: The endoplasmic reticulum enzyme UDP-glucose glycoprotein:glucosyltransferase (UGGT) has the unique property of recognizing incompletely folded glycoproteins and, if they carry an N -linked Man(9)GlcNAc(2)oligosaccharide, of catalyzing the addition of a glucose residue from UDP-glucose. Using peptide sequence information, we have isolated the complete cDNA of rat liver UGGT and expressed it in insect cells. The cDNA specifies an open reading frame which codes for a protein of 1527 residues including an 18 amino acid signal peptide. The protein has a C-terminal tetrapeptide (HEEL) characteristic of endoplasmic reticulum luminal proteins. The purified recombinant enzyme shows the same preference for unfolded polypeptides with N -linked Man(9)GlcNAc(2)glycans as the enzyme purified from rat liver. A genetically engineered Saccharomyces cerevisiae strain capable of producing glyco-proteins with Man(9)GlcNAc(2)core oligosaccharides was constructed and secreted acid phosphatase (G0-AcP) was purified. G0-AcP was used as an acceptor glycoprotein for UGGT and found to be a better substrate than the previously used soybean agglutinin and thyroglobulin. Recombinant rat UGGT has a K (m) of 44 microM for UDP-glucose. A proteolytic fragment of UGGT was found to retain enzymatic activity thus localizing the catalytic site of the enzyme to the C-terminal 37 kDa of the protein. Using site-directed mutagenesis and photoaffinity labeling, we have identified residues D1334, D1336, Q1429, and N1433 to be necessary for the catalytic activity of the enzyme.
authors.affiliation: Genetics Group, Biotechnology Research Institute, National Research Council of Canada, Montréal, Québec H4P 2R2, Canada.
authors.forename: D C
authors.initials: DC
authors.lastname: Tessier
authors.forename: D
authors.initials: D
authors.lastname: Dignard
authors.forename: A
authors.initials: A
authors.lastname: Zapun
authors.forename: A
authors.initials: A
authors.lastname: Radominska-Pandya
authors.forename: A J
authors.initials: AJ
authors.lastname: Parodi
authors.forename: J J
authors.initials: JJ
authors.lastname: Bergeron
authors.forename: D Y
authors.initials: DY
authors.lastname: Thomas
mesh_terms: D000135:Acid Phosphatase / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D016367:Baculoviridae / Q000235:genetics; D001665:Binding Sites; D002236:Carbohydrate Conformation; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D015870:Gene Expression; D005964:Glucosyltransferases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism; D008099:Liver / Q000201:enzymology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D019920:Photoaffinity Labels; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D018411:Spodoptera / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D018076:DNA, Complementary; D006023:Glycoproteins; D019920:Photoaffinity Labels; D011994:Recombinant Proteins; D005964:Glucosyltransferases; C072423:mannosylglycoprotein 1,3-glucosyltransferase; D000135:Acid Phosphatase