First evidence for occurrence of Galbeta1-3glcNAcbeta1-4Man unit in N-glycans of insect glycoprotein: Beta1-3gal and beta1-4glcNAc transferases are involved in N-glycan processing of royal jelly glycoproteins

On a way of structural analysis of total N-glycans linked to glycoproteins in royal jelly (Kimura, Y. et al., Biosci. Biotechnol. Biochem., 64, 2109-2120 (2000), Kimura, M. et al., Biosci. Biotechnol. Biochem., 66, 1985-1989 (2002)), we found that some complex type N-glycans containing a v1-3galactose residue occur on the insect glycoproteins. Up to date, it has been considered that naturally occurring insect glycoproteins do not bear the galactose-containing N-glycans, therefore, in this report we describe the structural analysis of the complex type N-glycans of royal jelly glycoproteins. By a combination of endo- and exo-glycosidase digestions, IS-MS analysis, and sup(1)H-NMR spectroscopy, the structures of the v1-3 galactose-containing N-glycan were identified as the following; GlcNAcv1-2Manalpha1-6[GlcNAcv1-2(Galv1-3GlcNAcv1-4)Manv1-3]Manv1-4GlcNAcv1-4GlcNAc,Manalpha1-3Manalpha1-6[GlcNAcv1-2(Galv1-3GlcNAcv1-4)Manalpha1-3]Manv1-4GlcNAcv1-4GlcNAc, and Manalpha1-6(Manalpha1-3)Manalpha1-6[GlcNAcv1-2(Galv1-3GlcNAcv1-4)Manalpha1-3]Manv1-4GlcNAcv1-4GlcNAc. To our knowledge, this is the first report showing that the Galv1-3GlcNAcv1-4Man unit occurs in N-glycans of insect glycoproteins, indicating a v1-3 galactosyl transferase and v1-4GlCNAC transferase (GNT-4) are expressed in the honeybee cells.