β₁ integrin is an adhesion protein for sperm binding to eggs

We investigated the role of β₁ integrin in mammalian fertilization and the mode of inhibition of fertilinβ-derived polymers. We determined that polymers displaying the Glu-Cys-Asp peptide from the fertilinβ disintegrin domain mediate inhibition of mammalian fertilization through a β₁ integrin receptor on the egg surface. Inhibition of fertilization is a consequence of competition with sperm binding to the cell surface, not activation of an egg-signaling pathway. The presence of the β₁ integrin on the egg surface increases the rate of sperm attachment but does not alter the total number of sperm that can attach or fuse to the egg. We conclude that the presence of β₁ integrin enhances the initial adhesion of sperm to the egg plasma membrane and that subsequent attachment and fusion are mediated by additional egg and sperm proteins present in the β₁ integrin complex. Therefore, the mechanisms by which sperm fertilize wild-type and β₁ knockout eggs are different.