Structural studies of a novel type of pentaantennary large glycan unit in the fertilization-associated carbohydrate-rich glycopeptide isolated from the fertilized eggs of Oryzias latipes

In a previous report (Kitajima, K., Inoue, S., and Inoue, Y. (1989) Dev. Biol. 132, 544-553), we found the presence of a heavily glycosylated polyprotein, 'H-hyosophorin,' isolated from the unfertilized eggs of Oryzias latipes. We now report our detailed analysis of the structure of the N- glycan chain in L-hyosophorin, the smallest repeating unit of H-hyosophorin, which was isolated from the fertilized eggs of O. latipes and formed from H- hyosophorin upon fertilization. The N-glycan structures were defined by a combination of compositional analysis, methylation analysis, selective chemical degradation (i.e. mild methanolysis, periodate-Smith degradation, and hydrazinolysis-nitrous acid deamination), enzymatic (endo-β- galactosidase, peptide:N-glycanase, and Newcastle disease virus sialidase) digestion, and instrumental analyses (one- and two-dimensional proton nuclear magnetic resonance spectroscopy and fast atom bombardment mass spectrometry) which revealed novel and unique features: (a) the presence of highly branched poly-N-acetyllactosamino pentaantennary structures; (b) the presence of a β- galactosylated Lewis X antigenic epitope, Galβ1→4 Galβ1→4 (Fucα1→3)GlcNAcβ1→; (c) the presence of a β-galactosylated sialyl Lewis X structure, Galβ1→4(Neu5Acα2→3)Galβ1→4(Fucα1→3)GlcNAcβ1→; (d) the presence of Galβ1→4Galβ1→ and Galβ1→ 4Galβ1→4Galβ1→ as the major and minor groupings, respectively; and (e) the presence of the branched Gal residues, →4GlcNAcβ1→3(Galβ1→4) Galβ1→. This study represents the first detailed investigation regarding the nature of highly branched complex asparagine-linked pentaantennary glycans in glycoproteins. The unique expression of such bulky multiantennary glycan units on proteins could be essential during early embryogenesis.