Species-specific sea urchin sperm protein required for adhesion of sperm to the egg surface during fertilization. Bindin coats the acrosomal process after it is externalized by the acrosome reaction. It binds to sulfated, fucose-containing polysaccharides on the vitelline layer receptor proteoglycans which cover the egg plasma membrane. A.punctulata bindin forms multilamellar structures reminiscent of lipid bilayers. Belongs to the bindin family.