Hamster sperm protein, P26h: A member of the short-chain dehydrogenase reductase superfamily

For successful fertilization to occur,mammalian spermatozoa must undergo a series of modifications in order to reach and penetrate the oocyte. Some of these modifications occur during passage through the epididymis, the site where spermatozoa acquire their fertilizing ability. We have previously des cribed hamster sperm protein, P26h, which is acquired by spermatozoa during epididymal transit, and have proposed that this protein is involved in spe rm-egg binding. In the present study, we report the cloning and characteriz ation of the full-length cDNA encoding hamster P26h. A database search usin g the predicted hamster P26h amino acid sequence revealed 85% identity with mouse AP27 protein and porcine carbonyl reductase, members of the short-ch ain dehydrogenase/reductase (SDR) family of proteins. Northern blot analysi s revealed a major P26h 1-kilobase transcript in the testis. No signal was detected in other somatic tissues of the hamster. In situ hybridization exp eriments revealed that the P26h gene was predominantly transcribed in semin iferous tubules of the testis and at a lower level in the corpus epididymid is. The identity of the cloned P26h was confirmed by immunoprecipitating in vitro-translated P26h using polyclonal antiserum raised against purified h amster sperm P26h. Taken together, these results identify P26h as a new mem ber of the SDR family of proteins involved in the processes of mammalian ga mete interactions.