Multivalent Fertilinβ Oligopeptides: The Dependence of Fertilization Inhibition on Length and Density

The sperm protein fertilinβ, 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 fertilinβ, 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.