Branching and elongation with lactosaminoglycan chains of N-linked oligosaccharides result in a shift toward termination with alpha 2-->3-linked rather than with alpha 2-->6-linked sialic acid residues.
The activity of bovine colostrum CMP-NeuAc:Gal beta 1-->4GlcNAc beta-R alpha 2-->6-sialyltransferase (alpha 6-NeuAcT) toward oligosaccharides that form part of complex-type, N-linked glycans appears significantly reduced when a bisecting GlcNAc residue or additional branches are present, or when core GlcNAc residues are absent. By contrast human placenta CMP-NeuAc:Gal beta 1-->4GlcNAc beta-R alpha 2-->3-sialyltransferase (alpha 3-NeuAcT) is much less sensitive to structural variations in these acceptors. Furthermore the alpha 3-NeuAcT shows a much higher activity than the alpha 6-NeuAcT with oligosaccharides that form part of linear and branched lactosaminoglycan extensions. These results indicate that, in tissues that express both enzymes, branching and lactosaminoglycan formation of N-linked glycans will cause a shift from termination with alpha 2-->6-linked sialic acid to termination with alpha 2-->3-linked sialic acid residues. These findings provide an enzymatic basis for the sialic acid linkage-type patterns found on the oligosaccharide chains of N-glycoproteins.
Nemansky
M
M
Department of Medical Chemistry, Vrije Universiteit, Amsterdam, The Netherlands.
Schiphorst
W E
WE
Van den Eijnden
D H
DH
D000606:Amino Sugars / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D002240:Carbohydrate Sequence; D002417:Cattle; D003126:Colostrum / Q000737:chemistry*; D006801:Humans; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000378:metabolism; D010920:Placenta / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry* / Q000378:metabolism; D012799:Sialyltransferases / Q000378:metabolism*; D013379:Substrate Specificity
D000606:Amino Sugars; D009844:Oligosaccharides; D011134:Polysaccharides; C039448:lactosaminoglycan; D012799:Sialyltransferases