The sperm protein fertilinbeta, a member of the ADAM family of proteins, is implicated in sperm-egg binding in all mammals studied to date. Multivalent inhibitors containing the three amino acid binding sequence of fertilinbeta, ECD, have been shown previously to be more effective inhibitors of fertilization than their monovalent counterparts. Here, we probed sperm-egg interactions with ruthenium-catalyzed ring-opening metathesis polymers that contained from 3 to 70 ECD pharmacophores in densities ranging from 10% to 100%. Evaluation of the polymer potencies, and synthesis of a triblock copolymer from two building blocks, revealed that two multivalent contacts are sufficient for maximal inhibition, and that the distance between ECD pharmacophores required is 7-9 monomers spanning 4-5 nm. We conclude that inhibition requires recruitment of two receptors on the egg surface into an inhibitory complex.

We investigated the role of β 1 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 β 1 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 β 1 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 β 1 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 β 1 integrin complex. Therefore, the mechanisms by which sperm fertilize wild-type and β 1 knockout eggs are different.

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