Sulfated α-L-galactans from the sea urchin ovary: Selective 6-desulfation as eggs are spawned

Abstract

The sea urchin eggs are surrounded by a jelly coat, which contains sulfated polysaccharides with unique structures. These molecules are responsible for inducing the species-specific acrosome reaction, an obligatory event for the binding of sperm and fusion with the egg. The mechanism of biosynthesis of these sulfated polysaccharides is virtually unknown. The egg jelly of the sea urchin Echinometra lucunter contains a simple 2-sulfated, 3-linked α-L-galactan. Here, we pulse labeled the sea urchin ovary in vitro with 35S-sulfate to follow the biosynthesis of the sulfated α-L-galactan. We found that the ovary contains a 2,6-disulfated, 3-linked α-L-galactan, which incorporates 35S-sulfate more avidly than the 2-sulfated isoform. The 2,6-disulfated α-L-galactan was purified by anion exchange chromatography, analyzed by electrophoresis and characterized by 1D and 2D nuclear magnetic resonance spectra. We also investigated the location of the sulfated polysaccharides on the oocytes using histochemical procedures. The stain revealed high amounts of sulfated polysaccharide in mature oocytes and accessory cells. The amount of intracellular sulfated polysaccharides decreased as oocytes are spawned. We speculate that 2,6-disulfated galactan is initially synthesized in the ovary and that 6-sulfate ester is removed when the polysaccharide is secreted into the egg jelly. Similar events related to remodeling of sulfated polysaccharides have been reported in other biological systems. © The Author 2010. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org.