Practice question

Bindin is a thirty-five kilodalton insoluble protein sequestered within sperm acrosomal vesicle and exposed at tip of acrosomal process after calcium-dependent exocytosis. It contains lectin-like domains recognizing sulfated polysaccharides on Egg Bindin Receptor EBR1 glycoprotein embedded in vitelline envelope. Interaction confers species-specific binding, constituting major barrier to heterospecific fertilization and reproductive isolation. Beyond adhesion, bindin exhibits amphipathic fusogenic activity promoting mixing of sperm and egg lipid bilayers facilitating membrane fusion. It does not power dynein-driven motility, regulate intracellular alkalization, or mediate chromatin condensation occurring during spermiogenesis.