Glycobiology Advance Access originally published online on August 12, 2008
Glycobiology 2008 18(11):882-890; doi:10.1093/glycob/cwn077
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Caenorhabditis elegans N-glycans containing a Gal-Fuc disaccharide unit linked to the innermost GlcNAc residue are recognized by C. elegans galectin LEC-6
2 Department of Biological Chemistry, School of Pharmaceutical Science, Teikyo University, 1091-1 Suarashi, Sagamiko, Sagamihara, Kanagawa 229-0195, Japan
3 Lectin Application and Analysis Team, Research Center for Medical Glycoscience, AIST, Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
1 To whom correspondence should be addressed: Tel: +81-42-685-3741; Fax: +81-42-685-3742; e-mail: t-take{at}pharm.teikyo-u.ac.jp
Received on July 9, 2008; revised on August 4, 2008; accepted on August 5, 2008
We report a detailed structural analysis of the N-glycans of Caenorhabditis elegans recognized by C. elegans galectin LEC-6. Glycoproteins of C. elegans captured by an immobilized LEC-6 affinity adsorbent were isolated. The N-glycans of these glycoproteins were then liberated by hydrazinolysis and labeled with the fluorophore 2-aminopyridine (PA). The derived pyridylaminated (PA)-sugars were further fractionated by rechromatography on immobilized LEC-6 adsorbent and by reversed-phase high-performance liquid chromatography (HPLC). The structures of the PA-sugars thus obtained were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS/MS) in conjunction with glycosidase digestion. We confirmed that all PA-sugars having affinity for LEC-6 contain a Gal-Fuc disaccharide unit, and that this unit is bound to the innermost GlcNAc residue of the N-glycan chain. The dissociation constants of LEC-6 for these glycans were measured by frontal affinity chromatography. LEC-6 exhibited higher affinity for oligosaccharides having a Gal-Fuc unit linked to position 6 of the innermost GlcNAc residue than for those having Galβ1-4GlcNAc units. Affinity for the former disappeared, however, following treatment with β-galactosidase. If the glycan contained a Hex-Fuc disaccharide linked to the penultimate GlcNAc residue, the affinity would be diminished. We propose, therefore, that the galectins of C. elegans utilize the Gal-Fuc disaccharide unit for recognition instead of the Gal-GlcNAc unit that is common in vertebrates.
Key words: Caenorhabditis elegans / core chitobiose modifications / frontal affinity chromatography / galectin / N-glycan
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