The present invention provides compositions and methods useful for regulating fertilization and for use as a contraceptive based on the discovery herein of an oocyte specific protein, SAS1R (Sperm Acrosomal SLLP1 Receptor), which is a sperm protein receptor. Six SAS1R variants, including the full length SAS1R, were identified. mSLLP1 and SAS1R co-localized to oocytes and to acrosomes of acrosome-reacted sperm. Interactions between mSLLP1 and SAS1R were demonstrated by far-western analysis, in a yeast two-hybrid system under stringent selection conditions, and by immunoprecipitation of SAS1R by anti-mSLLP1 as well as the converse. Purified recombinant SAS1R was found to have protease activity, to inhibit fertilization in-vitro, and to induce an immune response in females. Together, the results suggest SAS1R is a proteolytically active, oocyte and early embryo specific oolemmal metalloprotease receptor for the sperm intra-acrosomal ligand SLLP1 and is a target for regulating fertilization and as a contraceptive.
