A mammalian epididymal protein with remarkable sequence similarity to snake venom haemorrhagic peptides

Following spermatogenesis in the testis, mammalian spermatozoa pass into the epididymis, where they undergo changes which confer on them forward motility and the ability to recognize and penetrate the egg. Many of these maturation events involve androgen-regulated epididymal proteins which become associated with the sperm membrane, and/or effect changes to integral sperm membrane proteins. Here we report the sequence of an 89 kDa androgen-regulated protein from rat (Rattus norvegicus) and monkey (Macaca fascicularis) epididymis that is synthesized exclusively in the caput region and is localized on the apical surface of its principal epithelial cells. This protein shows remarkable similarity to a variety of proteases and disintegrins found in snake venoms and is similar to, but distinct from, the guinea-pig sperm surface PH-30 alpha/beta complex recently implicated in sperm-egg recognition and fusion.