Location of N-unsubstituted glucosamine residues in heparan sulfate.
Functional properties of heparan sulfate (HS) are generally ascribed to the sulfation pattern of the polysaccharide. However, recently reported functional implications of rare N-unsubstituted glucosamine (GlcNH(2)) residues in native HS prompted our structural characterization of sequences around such residues. HS preparations were cleaved with nitrous acid at either N-sulfated or N-unsubstituted glucosamine units followed by reduction with NaB(3)H(4). The labeled products were characterized following complementary deamination steps. The proportion of GlcNH(2) units varied from 0.7-4% of total glucosamine in different HS preparations. The GlcNH(2) units occurred largely clustered at the polysaccharide-protein linkage region in intestinal HS, also more peripherally in aortic HS. They were preferentially located within N-acetylated domains, or in transition sequences between N-acetylated and N-sulfated domains, only 20-30% of the adjacent upstream and downstream disaccharide units being N-sulfated. The nearest downstream (toward the polysaccharide-protein linkage) hexuronic acid was invariably GlcUA, whereas the upstream neighbor could be either GlcUA or IdoUA. The highly sulfated but N-unsubstituted disaccharide unit, -IdoUA2S-GlcNH(2)6S-, was detected in human renal and porcine intestinal HS, but not in HS from human aorta. These results are interpreted in terms of a biosynthetic mechanism, whereby GlcNH(2) residues are formed through regulated, incomplete action of an N-deacetylase/N-sulfotransferase enzyme.
Westling
Camilla
C
Department of Medical Biochemistry and Microbiology, The Biomedical Center, Uppsala University, P. O. Box 582, SE-75123 Uppsala, Sweden.
Lindahl
Ulf
U
D000818:Animals; D001011:Aorta / Q000378:metabolism; D002240:Carbohydrate Sequence; D002850:Chromatography, Gel; D004187:Disaccharides / Q000737:chemistry; D005944:Glucosamine / Q000737:chemistry*; D006497:Heparan Sulfate / Q000737:chemistry* / Q000378:metabolism; D006603:Hexuronic Acids / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007668:Kidney; D009608:Nitrous Acid / Q000737:chemistry; D009844:Oligosaccharides / Q000737:chemistry; D011134:Polysaccharides / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013552:Swine
D004187:Disaccharides; D005944:Glucosamine; D006497:Heparan Sulfate; D006603:Hexuronic Acids; D009608:Nitrous Acid; D009844:Oligosaccharides; D011134:Polysaccharides