Bindin receptors in sea urchins are located on the:
Species-specific sperm binding occurs on vitelline envelope where Egg Bindin Receptor glycoprotein complex is concentrated. Biochemical isolation shows EBR1 is 350 kDa transmembrane protein with large extracellular domain containing sulfated oligosaccharides recognized by bindin lectin domain. Immunofluorescence localizes EBR1 to vitelline envelope before fertilization, not soluble jelly, internal cortical granules, or deep plasma membrane domains. After cortical granule serine protease cleaves EBR1 extracellular domain, binding sites are lost, contributing to permanent block. Egg plasma membrane contains fusogenic lipids and integrins mediating final membrane merger after initial vitelline anchoring, but primary bindin receptor resides in envelope.
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Localization of bindin receptor EBR1 on vitelline envelope.