Fertilization antigen-1: cDNA cloning, testis-specific expression, and immunocontraceptive effects

cDNA encoding for a sperm antigen, designated fertilization antigen (FA-1), was cloned and sequenced from murine testis cDNA-λgt11 expression library using FA-1 mAb. Computer-generated translation analysis of 649-bp cDNA yielded an ORF of 164 amino acids with the first ATG Met start codon at nucleotide 81 and the stop codon TAA at nucleotide 577 and a polyadenylylation tail following the stop codon. The translated protein has a calculated molecular mass of 18.2 kDa and a potential N-linked glycosylation site at amino acids 158–160, besides at least two O-linked glycosylation sites. The hydropathy plot generated from the deduced amino acid sequence indicated it to be a membrane-anchored peptide. Extensive computer search in the GenBank, National Biomedical Research Foundation, and Swiss sequence banks did not identify any known nucleotide/amino acid sequence having homology with FA-1 cDNA or deduced amino acids, indicating it to be a novel protein. Northern blot analysis and reverse transcription–PCR indicated testis-specific expression of FA-1 antigen. The FA-1 cDNA was subcloned into pGEX-2T vector and expressed in glutathione S-transferase gene fusion system to obtain the recombinant protein. The recombinant protein specifically reacted with ZP3 of oocyte zona pellucida and its affinity-purified antibodies completely blocked sperm–zona pellucida interaction in mice. These findings suggest that the sperm-specific recombinant FA-1 antigen is an attractive candidate for the development of a contraceptive vaccine.