title: Location of the glucuronosyltransferase domain in the heparan sulfate copolymerase EXT1 by analysis of Chinese hamster ovary cell mutants.
abstract: Heparan sulfate formation occurs by the copolymerization of glucuronic acid (GlcA) and N-acetylglucosamine (GlcNAc) residues. Recent studies have shown that these reactions are catalyzed by a copolymerase encoded by EXT1 and EXT2, members of the exostosin family of putative tumor suppressors linked to hereditary multiple exostoses. Previously, we identified a collection of Chinese hamster ovary cell mutants (pgsD) that failed to make heparan sulfate (Lidholt, K., Weinke, J. L., Kiser, C. S., Lugemwa, F. N., Bame, K. J., Cheifetz, S., Massagué, J., Lindahl, U., and Esko, J. D. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 2267-2271). Here, we show that pgsD mutants contain mutations that either alter GlcA transferase activity selectively or that affect both GlcNAc and GlcA transferase activities. Expression of EXT1 corrects the deficiencies in the mutants, whereas EXT2 and the related EXT-like cDNAs do not. Analysis of the EXT1 mutant alleles revealed clustered missense mutations in a domain that included a (D/E)X(D/E) motif thought to bind the nucleotide sugar from studies of other transferases. These findings provide insight into the location of the GlcA transferase subdomain of the enzyme and indicate that loss of the GlcA transferase domain may be sufficient to cause hereditary multiple exostoses.
authors.affiliation: Department of Cellular and Molecular Medicine, Glycobiology Research and Training Program, University of California, San Diego, La Jolla, California, 92093-0687, USA.
authors.forename: G
authors.initials: G
authors.lastname: Wei
authors.forename: X
authors.initials: X
authors.lastname: Bai
authors.forename: M M
authors.initials: MM
authors.lastname: Gabb
authors.forename: K J
authors.initials: KJ
authors.lastname: Bame
authors.forename: T I
authors.initials: TI
authors.lastname: Koshy
authors.forename: P G
authors.initials: PG
authors.lastname: Spear
authors.forename: J D
authors.initials: JD
authors.lastname: Esko
mesh_terms: D000117:Acetylglucosamine / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D003001:Cloning, Molecular; D006224:Cricetinae; D005097:Exostoses, Multiple Hereditary; D014453:Glucuronosyltransferase / Q000378:metabolism*; D006497:Heparan Sulfate / Q000235:genetics*; D006801:Humans; D007700:Kinetics; D051379:Mice; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D017351:N-Acetylglucosaminyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D000099065:Exostosin 2; D000099058:Exostosin 1
chemical_list: D000117:Acetylglucosamine; D014453:Glucuronosyltransferase; D006497:Heparan Sulfate; D017351:N-Acetylglucosaminyltransferases; D011506:Proteins; D011994:Recombinant Proteins; D000099065:Exostosin 2; D000099058:Exostosin 1