Serine protease inhibitor that plays an essential role in male reproduction and fertility. Modulates the hydrolysis of SEMG1 by KLK3/PSA (a serine protease), provides antimicrobial protection for spermatozoa in the ejaculate coagulum, and binds SEMG1 thereby inhibiting sperm motility (By similarity).
Subcellular locations: Secreted
Bound to the surface of testicular and on the head and tail of ejaculate spermatozoa.