First evidence for occurrence of galβ1-3GlcNAcβ1-4man unit in N-glycans of insect glycoprotein: β1-3gal and β1-4GlcNAc 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 β1-3galactose 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 ¹H-NMR spectroscopy, the structures of the β1-3 galactose-containing N-glycan were identified as the following; GlcNAcβ1-2Manα1-6[GlcNAcβ1-2(Galβ1-3GlcNAcβ1-4)Manα1-3]Manβ1-4GlcNAcβ1-4GlcNAc, Manα1-3Manα1-6[GlcNAcβ1-2(Galβ1-3GlcNAcβ1-4)Manα1-3]Manβ1-4GlcNAcβ1-4GlcNAc, and Manα1-6(Manα1-3)Manα1-6[GlcNAcβ1-2(Galβ1-3GlcNAcβ1-4)Manα1-3]Manβ1-4GlcNAcβ1-4GlcNAc. To our knowledge, this is the first report showing that the Galβ1-3GlcNAcβ1-4Man unit occurs in N-glycans of insect glycoproteins, indicating a β1-3 galactosyl transferase and β1-4GlcNAc transferase (GNT-IV) are expressed in the honeybee cells.