Fertilinβ peptidic liposomes inhibit fertilization by steric blockage

Liposomes presenting fertilinβ peptides are inhibitors of mouse in vitro fertilization. We undertook a study of the relationship between IC50 and mole fraction of fertilinβ in the liposome, and the size dependence of inhibition of fertilization to understand the mechanism of their inhibition. Our results indicate that a small number of multivalent contacts are required for efficient attachment of inhibitor to receptor on the target membrane, and that, as designed, the liposomes target the egg membrane but not the sperm membrane. The size dependence of the liposome inhibition demonstrates that the liposomes physically block access of the sperm to the egg membrane thereby preventing sperm binding to all egg receptors not just the fertilinβ receptor.