A major flagellum sialoglycoprotein in sea urchin sperm contains a novel polysialic acid, an alpha2,9-linked poly-N-acetylneuraminic acid chain, capped by an 8-O-sulfated sialic acid residue.

A new type of polysialic acid (polySia) structure was demonstrated to occur in a major unknown sialoglycoprotein with a diverse molecular mass of 40-80 kDa in sea urchin sperm. The polySia-containing glycan structure was determined to be HSO(3)-->8Neu5Acalpha2-->9(Neu5Acalpha2-->9)(n-2) Neu5Acalpha2-->6GalNAcalpha1-->Ser/Thr (n, on average 15), based on carbohydrate analysis of the sialoglycopeptide obtained by an exhaustive protease digestion of whole sperm, fluorometric anion-exchange high-performance liquid chromatography, and methylation analysis. The sulfate group was predominantly localized to the nonreducing terminus of the polySia chain. This is the first example of an alpha2,9-linked polySia structure in animal sperm. The polySia-containing sialoglycoprotein was present in sperm flagellum but not in the head. Furthermore, this sialoglycoprotein localized in the sperm lipid raft, which contains an enriched ganglioside (Neu5Acalpha2-->8Neu5Acalpha2-->6GlcCer), a receptor for sperm-activating peptide (speract), and its associated guanylate cyclase.