Basic studies on sperm-egg binding and applications to contraception

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We founs a novel sperm protein sp38 with zona pellucida (ZP)-binding activity located at the anterior portion of many mammalian species. It was originally purified from boar epididymal sperm as a 38 kDa glycoprotein. The cDNA clones encoding sp38 was isolated from boar testis cDNA library based on the results of partial amino acid sequences of purified protein. The cDNA encoded a 350-residue amino acid precursor protein which was posttranslationally modified into a mature protein of 299 amino acid residues. Northern blot analysis demonstrated that the transcript of sp38 was expressed only in the testis. Mouse and human homologues of boar sp38 was obtained from testis sDNA libraries of respective species and showed highly homologous sequences. Boar sp38 bound to 90kDa-ZP glycoprotein species in a calcium-dependent manner. The binding characteristics of sp38 to the ZP were similar to those of proacrosin. Antibodies against sp38 inhibited the binding of sperm to the ZP in vitro egg-sperm binding assay.