The long term objective of the research is to provide a molecular mechanism for the block to polyspermy reaction at fertilization. This reaction is a fundamental step in the fertilization process insuring that the diploid state of the chromosomes, one restored by fusion of sperm and egg nuclei, is maintained. Knowledge of the molecular mechanisms of the polyspermy reaction will permit its control. Infertility caused by defects in this reaction may be overcome and prevention of fertilization (contraception) can potentially use this mechanism based on a fundamental understanding of the process. A lectin-ligand hypothesis for blocking sperm penetration has been proposed. The egg cortical granule lectin released in the sperm triggered cortical reaction has been isolated, cloned and characterized as a glycoprotein binding molecule. However, the oviductally secreted glycoprotein ligand has not been structurally and functionally characterized. The specific aims of this application are: 1) determine the structural relation of two forms of the isolated ligand using immunological, amino acid sequencing, and cloning methods. 2) characterize the functional properties of the isolated ligand by: a) reproducing the ultrastructure of the in situ lectin-ligand reaction (the so-called fertilization layer) using isolated lectin and ligand, b) establish the extracellular matrix location of the ligand using immunocytochemical methods, and c) determine if the ligand binds to sperm via its carbohydrate moieties and functions as a ligand for a sperm surface receptor. Results from the proposed research will provide a structural understanding for the cortical granule lectin ligand and test the hypothesis that the ligand also plays a fertilization role in binding to sperm.