Bindin,a multifunctional sperm ligand and the evolution of new species

Sea urchin sperm species-specifically adhere to the egg surface during fertilization. The protein which mediates this adhesion is known as bindin and cDNAs have recently been cloned and sequenced from several different species. Bindin proteins contain a highly conserved central domain flanked by much more highly divergent amino- and carboxyl-terminal domains. Investigations of the structure and function relationships indicate that the conserved domains may participate in membrane fusion and sulfated fucan binding activities, which may be conserved functions of bindin. The species-specific adhesion activity appears to be duplicated in both the amino- and carboxyl-terminal domain and may correspond to repeated sequence motifs found in these domains. The duplication of these sequence motifs and the redundancy of the adhesive domains may be important for the molecular mechanism of bindin evolution during speciation.