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 fucose-rich polysaccharides and sia lic acid-rich glycoproteins. Chemical and 500 MHz H-1 NMR spectroscopi c studies revealed for the first time the presence of a novel polysial ic acid (polySia) structure in the jelly coat glycoproteins isolated f rom Hemicentrotus pulcherrimus (designated polySia-gp(H)). The structu re of the polySia chains was thoroughly characterized as (-->5-O-glyco lyl-Neu5Gc alpha 2-->)(n), where n ranges from 4 to more than 40 Neu5G c residues. The polyNeu5Gc chains were attached to core oligosaccharid es that were O-glycosidically linked to threonine residues on a core p olypeptide. Each polypeptide contained about 17 O-linked polysialylgly can 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 poly Sia-gp from other known polysialylated glycoproteins. The (-->5-O-glyc olyl-Neu5Gc alpha 2-->)(n), chains were resistant to exo- and endosial idases from Arthrobacter ureafaciens and bacteriophage K1F, respective ly. Discovery of these (-->5-O-glycolyl-Neu5Gc alpha 2-->)(n) chains a dds a new class of naturally occurring polySia to the structurally div erse family of polysialylated glycoproteins. The structure of a polySi a-gp hom a different sea urchin species, Strongylocentrotus purpuratus (designated polySia-gp(S)), was also determined to ascertain if there were any species-specific differences. The 500 MHz H-1 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 polySia-gp(S) was larger, however (250,000), and it contained about 2 5 polySia chains O-glycosidically linked to both threonine (two-thirds ) and serine (one-third) residues.