Probably inhibits protein phosphatase 1 (PP1) in sperm via binding to catalytic subunit PPP1CC. Interacts (via RVxF motif) with PPP1CC. Expressed in testis, epididymis and spermatozoa (at protein level). Not expressed in brain, heart, lung, liver, spleen, kidney and skeletal muscle. Detected in testis 25 days after birth and thereafter. This protein is not related to the claudin family.