Secreted proximal epididymal protein required for post-testicular sperm maturation and male fertility. May be involved in sperm adhesion to the egg zona pellucida. Does not have ribonuclease activity (By similarity). Male-specific expression in proximal caput of the epididymis. The N-terminus is blocked. Glycosylated (By similarity). Belongs to the pancreatic ribonuclease family.