350-kDa Royal Jelly Glycoprotein (Apisin), Which Stimulates Proliferation of Human Monocytes, Bears the β1-3Galactosylated N-Glycan: Analysis of the N-Glycosylation Site

While doing a structural analysis of minor component N-glycans linked to 350-kDa royal jelly glycoprotein (RJGP), which stimulates the proliferation of human monocytes, we found that a Galβ1-3GlcNAcβ1-4Man unit occurs on the insect glycoprotein. The structure of the fluorescence-labeled N-glycan was analyzed by sugar component analysis, IS-MS, and 1 H-NMR. The structural analysis showed that the 350-kDa RJGP bears Galβ1-3GlcNAcβ1-4(GlcNAcβ1-2)Manα1-3 (Manα1-3Manα1-6)Manβ1-4GlcNAcβ1-4GlcNAc, suggesting this insect glycoprotein is one of the substrates for both β1-3 galactosyl and β1-4 N-acetylglucosamininyl transferases. To our knowledge, this is the first report that succeeded in identifing an insect glycoprotein bearing the β1-3 galactosylated N-glycan.