MAMMALIAN SPERM SURFACE MANNOSIDASE

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This project focuses on the biochemical characterization of sperm surface mannosidase, a glycohydrolase believed to have a receptor-like role in sperm-egg interaction and on its complimentary glycan units on rat zona pellucida. The enzyme is an intrinsic plasma membrane (PM) protein with its catalytic domain oriented towards the outer surface of the intact spermatozoa. Since the enzyme is optimally active near neutral pH, it would be functionally active in physiological settings during in vitro and in vivo fertilization. The PI has demonstrated: a) the presence of the precursor and mature forms of alpha-D-mannosidase in PMs from the testis and on spermatozoa from the caput and corpus. Only the mature form is present in the cauda sperm PM; b) that the enzyme is synthesized and partially processed to the mature form in rat testicular germ cells; c) the role of protein-conjugated sugar residues in the induction of the acrosome reaction of spermatozoa; d) the cloning and characterization of rat ZP glycoconjugates; and e) the functional significance of the rat sperm surface mannosidase. The aims of this application are a continuation of ongoing studies. The first aim is designed to examine biosynthesis, proteolytic processing, intracellular trafficking, and cell surface expression of the sperm mannosidase in spermatogenic cells in culture. The second aim is to obtain evidence for the presence of complementary bioactive glycan units on rat ZP glycoproteins. The third aim is to examine the functional significance of the glycans in the sperm-egg interaction and in sperm activation. The proposed studies are part of the investigators' long-term goal to identify and chemically characterize the complementary molecules from the surface of opposite gametes which initiate sperm-egg interaction. This project will examine one of the receptor and ligand moieties believed to be involved in fertilization. Data from these studies will provide information on the role of the sperm surface mannosidase in egg adhesion and sperm activation during fertilization in the rat and will provide insight into mechanisms underlying the high degree of species-specificity observed during the fertilization process.