To establish a systematic strategy for characterizing fertilization proteins of sperm cells, we prepared alloantisera by immunizing gilts with salt-washed membranes from boar spermatozoa. The antisera recognized a unique subset of sperm membrane proteins that migrated with Mr 7500–66 000 in SDS-PAGE under nonreducing conditions. The antisera did not recognize proteins of erythrocyte membranes, and tissue absorption experiments further confirmed that the alloantigens were sperm-specific proteins. Each of these sperm-specific membrane proteins (SSMPs) possessed one or more disulfide bonds that were essential for its interaction with alloantibody. Enzymatic deglycosylation revealed that most of the SSMPs were glycoproteins, and their alloantigenicity was not dependent on the presence of N-linked oligosaccharides. The presence of disulfide bonds and glycosylation indicated that the SSMPs identified each comprise at least one extracellular domain. Two-dimensional electrophoresis resolved at least 14 distinct SSMPs, 13 of which possessed acidic pIs (range 4.2–4.8). By indirect immunofluorescence, the SSMPs localized to the cell surface overlying all major regions of the sperm cell. We conclude that the repertoire of immunodominant SSMPs in the pig is relatively small, which makes feasible the systematic elucidation of their functions in fertilization.
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