The quest for the sea urchin egg receptor for sperm

This review discusses identification, isolation and characterization of proteins mediating species-selective sperm-to-egg adhesion during sea urchin fertilization. Bindin is the only sea urchin sperm protein known to mediate species-selective sperm attachment to eggs. Two completely different egg surface proteins, 350-kDa and EBR1, have affinity for bindin and each one meets all the criteria to be a species-selective sperm receptor. Experiments suggest that sperm bindin recognizes both the sulfated O-linked oligosaccharides on the egg 350-kDa glycoprotein, and also the repeated protein sequence modules of EBR1.