Isolation and characterization of proteolytic fragments of the sea urchin sperm receptor that retain species specificity.

The sea urchin sperm receptor isolated from the eggs of Strongylocentrotus purpuratus is a high molecular weight proteoglycan-like molecule. Previous studies in our laboratory suggested that the sperm receptor has two functional components, glycosaminoglycan chains that are responsible for sperm binding and polypeptide chains that control species specificity in the binding process. We have investigated this idea further by generating fragments of the receptor by limited proteolytic digestion of the egg cell surface. The results of experiments with these receptor preparations support the hypothesis that the species specificity of inhibition of fertilization observed in a competitive bioassay is conferred by the polypeptide portion of the receptor molecule. Studies with various receptor preparations reveal that the presence of at least 30% of the polypeptide by weight is required to inhibit fertilization species specifically. Receptor preparations containing less than 10% protein lack species specificity and inhibit fertilization in both S. purpuratus and Arbacia punctulata.