Isolation and sequencing of the cDNA encoding the 75-kD human sperm protein related to infertility.

Serum was obtained from an infertile woman (IS) inducing head-to-head agglutination of human sperm and was used to screen a human testis lambda gt11 cDNA library. A plaque producing the interacting antigen was located. The recombinant lambda gt11 was isolated and cut with EcoRI releasing a 0.7-kb cDNA. Using the 0.7-kb cDNA as a probe, a larger cDNA of 2.4 kb was isolated and its nucleotide sequence determined. It was composed of 2 427 nucleotides with an open reading frame of 1584 nucleotides encoding 528 amino acid residues. The specific antisperm antibody was isolated from IS by epitope selection, using positive plaques of E. coli Y1090. The epitope-selected antibodies interacted with a 75-kD human sperm protein and with a polypeptide in the form of a beta-galactosidase fusion protein in the recombinant lysate of E. coli Y1089, determined by immunoblot. The fusion protein was purified by affinity chromatography on an anti-beta-galactosidase-Sepharose column. It is proposed that production of anti-75-kD antibodies may be the underlying cause of the infertility.