Cloning of a glucose phosphate isomerase/neuroleukin-like sperm antigen involved in sperm agglutination

The mouse monoclonal antibody (mAb) A36 produced by us and shown to induce extensive, "tangled" sperm agglutination rues used to isolate cDNAs encodin g its cognate antigen. Three overlapping cDNA clones specifically recognize d by the mAb were isolated from a human testis cDNA expression library in l ambda gt11. Sequencing of these cDNAs yielded the complete nucleotide seque nce of a 3-kilobase cDNA that encodes the mAb-related polypeptide, designat ed sperm antigen-36 (SA-36), composed of 558 deduced amino acids. SA-36 cDN A contained a 5' untranslated region of 234 nucleotides (nt), an open readi ng frame of 1674 nt, and a 3' untranslated region of 1138 nt, SA-36 cDNA di splayed > 99% homology to glucose phosphate isomerase (GPI)/neuroleukin (NL K) mRNA, This surprising homology was confirmed in Western blots demonstrat ing that mAb A36 reacted specifically with GPI obtained from rabbit muscle and from baker's yeast. Moreover, polyclonal, monospecific antibodies produ ced against beta-galactosidase/SA-36-3 fusion protein stained human spermat ozoa and caused intensive agglutination of these cells in a manner similar to that with the mAb. Taken together, the data presented here demonstrated that mAb A36 cognate s perm surface antigen, encoded by SA-36 cDNA, is a GPI/NLK-like protein invo lved in sperm agglutination.