Identification of polysialic acid-containing glycoprotein in the jelly coat of sea urchin eggs. Occurrence of a novel type of polysialic acid structure.

Sea urchin eggs are surrounded by a gelatinous layer (called the jelly coat) that consists of mixture of fucoserich polysaccharides and sialic acid-rich glycoproteins. Chemical and 500 MHz 1H NMR spectroscopic studies revealed for the first time the presence of a novel polysialic acid (polySia) structure in the jelly coat glycoproteins isolated from Hemicentrotus pulcherrimus (designated polySia-gp(H)). The structure of the polySia chains was thoroughly characterized as (-->5-Oglycolyl-Neu5Gc alpha 2-->)n, where n ranges from 4 to more than 40 Neu5Gc residues. The polyNeu5Gc chains were attached to core oligosaccharides that were O-glycosidically linked to threonine residues on a core polypeptide. Each polypeptide contained about 17 O-linked polysialylglycan chains. The apparent molecular weight of polySia-gp(H) was 180,000. The expression of this new polySia structure in place of alpha 2-->8-linked polySia is the main structural feature that distinguishes polySia-gp from other known polysialylated glycoproteins. The (-->5-Ogly-colyl-Neu5Gc alpha 2-->)n chains were resistant to exo- and endosialidases from Arthrobacter ureafaciens and bacteriophage K1F, respectively. Discovery of these (-->5-Ogly-colyl-Neu5Gc alpha 2-->)n chains adds a new class of naturally occurring polySia to the structurally diverse family of polysialylated glycoproteins. The structure of a poly-Sia-gp from a different sea urchin species, Stronglyocentrotus purpuratus (designated polySia-gp(S)), was also determined to ascertain if there were any species-specific differences. The 500 MHz 1H NMR spectra of the two polySia-gps were identical, indicating that at this level of molecular detail the structures were the same. The molecular weight of polySiagp(S) was larger, however (250,000), and it contained about 25 polySia chains O-glycosidically linked to both threonine (two-thirds) and serine (one-third) residues.