A precise structural analysis of a fertilization-associated carbohydrate-rich glycopeptide isolated from the fertilized eggs of euryhaline killi fish (Fundulus heteroclitus). Novel penta-antennary N-glycan chains with a bisecting N-acetylglucosaminyl residue

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Abstract
A novel carbohydrate-rich sialoglycopeptide of apparent molecular mass $$$6 kDa was isolated from the fertilized eggs of Fundulus heteroclitus (euryhaline killi fish). This glycopeptide is a member of the L-hyosophorin family, characterized by its high content of carbohydrate (80–90% by weight) and formed by depolymerization of the precursor glycopolyprotein (H-hyosophorin) upon fertilization. The structures of the N-glycan chains were unambiguously established by a combination of compositional analysis, methylation analysis, selective chemical degradation (periodate oxidation-Smith degradation and hydrazinolysis-nitrous acid deamination), enzymatic (peptide:N-g]ycosidase F, several β-galactosidases, (β-hexosaminidase and α-galactosidase) digestions and instrumental analyses (1H-NMR and fast atom bombardment mass spectrometry) to have the novel and unique carbohydrate sequences, Galα1→3(Galβ1→4)Ga1β1→4GlcNAcβ1→ and Galα1→3(±GalNAcβ1→4GlcNAcβ1→3Galβ1→4)Gal-β1→4GlcNAcβ1→. This study represents the first detailed investigation of the nature of bulky complex asparagine-linked penta-antennary glycans with a bisecting GlcNAc residue in glycoproteins. Expression of such bulky multiantennary glycan units on proteins may be essential during early embryogenesis.

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