Practice question

Bindin represents classic example of rapidly evolving reproductive protein under positive selection driving speciation. It is insoluble acrosomal protein retained on acrosomal process after exocytosis, contacting vitelline envelope receptor EBR1. Sequence analysis reveals lectin domains mediating species-specific adhesion plus amphipathic helical regions destabilizing membranes promoting fusion, qualifying as fusogenic. It is not jelly component dissolving in seawater, not cortical granule enzyme released by egg, nor constituent of hardened fertilization envelope that consists of crosslinked vitelline glycoproteins. Its localization strictly on sperm ensures sperm side contributes adhesive and fusogenic activity essential for membrane merger and reproductive isolation.