Required for normal acrosome reaction and for normal male fertility (By similarity). Can bind Cu(2+) (PubMed:15218028, PubMed:20411530). Expressed in testis, in Sertoli cells, ejaculated spermatozoa and in seminal fluid (at protein level). A short helical region is required and sufficient for Cu(2+) binding. N-glycosylated. N-glycosylated at two distinct sites. O-glycosylated. Belongs to the prion family.