Occurrence of GalNAcβ1-4GlcNAc Unit in N-Glycan of Royal Jelly Glycoprotein

Elsewhere, we characterized the structure of twelve N-glycans purified from royal jelly glycoproteins (Kimura, Y. et al., Biosci. Biotechnol. Biochem., 64, 2109-2120 (2000)). Structural analysis showed that the typical high-mannose type structure (Man9-4GlcNAc2) accounts for about 72% of total N-glycans, a biantennary-type structure (GlcNAc2Man3GlcNAc2) about 8%, and a hybrid-type structure (GlcNAc1Man4GlcNAc2) about 3%. During structural analysis of minor N-glycans of royal jelly glycoproteins, we found that one had an N-acetyl-galactosaminyl residue at the non reducing end; most of such residues have been found in N-glycans of mammalian glycoproteins. By exoglycosidase digestion, methylation analysis, ion-spray (IS)-MS analysis, and ¹H NMR spectroscopy, we identified the structure of the N-glycan containing GalNAc as; GlcNAcβ1-2Manα1-6(GalNAcβ1-4GlcNAcβ1-2Manα1-3)Manβ1-4GlcNAcβ1- 4GlcNAc. This result suggested that a β1-4 GalNAc transferase is present in hypopharyngeal and mandibular glands of honeybees.