Charge interactions in sperm-egg recognition

A novel method using derivatized agarose beads for investigating the types of molecules, when isolated from all others, that can form stable adhesive bonds, was recently described by Roque et al. (1996). The findings from this study were extended to living sea urchin cell systems. Both the bead results and the experiments with sea urchin cells suggested that phosphorylated amino acids can form stable adhesive bonds with positively charged peptides (Roque et al., 1996). As these experiments only examined phosphorylated amino acids, the validity of the hypotheses developed in the earlier study was dependent on extending the experiments to additional phosphorylated molecules. In this study, effects of D-mannose, D-mannose-1-phosphate, D-fructose, D-fructose-1-phosphate, maltose and maltose-1-phosphate on embryo cell reaggregation and sperm-egg interaction using untreated, jelly coat-free and vitelline layer disrupted Strongylocentrotus purpuratus sea urchin eggs were examined. The phosphorylated sugars (50 mM), and not their non-phosphorylated counterparts, strongly inhibited fertilization of the 3 types of eggs. ATP, at concentrations as low as 0.8 mM also completely inhibited fertilization. The phosphorylated sugars had little or no effect on reaggregating sea urchin blastula cells. A likely explanation of these results is that sperm-egg interaction in the sea urchin involves positively and negatively charged receptors; the positively charged receptors are blocked by exogenously added phosphorylated molecules. These and earlier studies indicate that by extending results from bead modeling studies to living systems, interesting information can be obtained regarding bonding mechanisms that may modulate adhesive interactions.