Fertilin is a member of the ADAM super family of extracellular matrix proteins containing disintegrin and metalloprotease domains that are known to function in fertilization, myoblast fusion, neurogenesis, and shedding of receptor ectodomains. Fertilin is present on the extracellular surface of sperm, and binds to the alpha6beta1 integrin on the egg. The goal of these studies is to explore the role of other ADAM proteins present on the sperm surface, as well as to investigate the fertilinbeta- alpha6beta1 integrin ligand-receptor pair. Specific questions that will be addressed are: 1) What are the functions of other ADAM proteins on the sperm surface, and do they have their own adhesion partners? Photoaffinity labeling experiments will be used to address this question. 2) What is the required density of sperm ADAM ligands for maximal inhibition of sperm-egg adhesion? Polyvalent molecules and membrane mimics will be synthesized and tested as inhibitors of in vitro fertilization. 3) Does binding of sperm ADAMs to egg integrins cause egg activation? The polyvalent probes prepared in aim number 2 will be tested to see if they initiate cortical granule exocytosis, Ca2+ oscillations or second polar body formation. 4) What controls the function of alpha6beta1 integrin? The binding affinity and avidity of fertilinbeta for alpha6beta1 on the egg will be determined as a function of three stimuli: divalent cations, activating beta1 antibody, and an EGF-like peptide from fertilinbeta. These studies will investigate what regulates the binding of alpha6beta1 to its two known ligands, fertilinbeta and laminin. The significance of the work proposed is 2-fold. (i) To understand at the molecular level the affinities and specificities of ADAM proteins for their receptors and hence their function. (ii) To elucidate what initiates signaling pathways in fertilization and egg activation. These results will give insight into the functions of ADAM disintegrins in many physiological processes such as myoblast fusion and neurogenesis, in addition to fertilization. In addition, they will contribute to understanding the reasons for infertility and to the development of new approaches to contraception.
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