Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 278, Issue 44, Pages 43102-43109Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M308255200
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A novel beta1,6-N-acetylglucosaminyltransferase (beta1, 6GnT) cDNA was identified by a BLAST search using the amino acid sequence of human GnT-V as a query. The full-length sequence was determined by a combination of 5'-rapid amplification of cDNA end analysis and a further data base search. The open reading frame encodes a 792 amino acid protein with a type II membrane protein structure typical of glycosyltransferases. The entire sequence identity to human GnT-V is 42%. When pyridylaminated (PA) agalacto biantennary N-linked oligosaccharide was used as an acceptor substrate, the recombinant enzyme generated a novel product other than the expected GnT-V product, (GlcNAc beta1,2-Manalpha1,3-)[GlcNAcbeta1,2-(GlcNAcbeta1,6-)Manalpha1,6-] Manbeta1,4-GlcNAcbeta1,4-GlcNAc-PA. This new product was identified as [GlcNAcbeta1,2-(GlcNAcbeta1,6-)Manalpha1,3-][GlcNAcbeta1,2-(GlcNAcbeta1,6-)Manalpha1,6-]Manbeta1,4-GlcNAcbeta1,4-GlcNAc-PA by mass spectrometry and H-1 NMR. Namely, the new GnT (designated as GnT-IX) has beta1,6GnT activity not only to the alpha1,6-linked mannose arm but also to the alpha1,3-linked mannose arm of N-glycan, forming a unique structure that has not been reported to date. Northern blot analysis showed that the GnT-IX gene is exclusively expressed in the brain, whereas the GnT-V gene is expressed ubiquitously. These results suggest that GnT-IX is responsible for the synthesis of a unique oligosaccharide structure in the brain.
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