CatSper (CATionic channel of SPERm), a pH regulated, principal flagellar calcium ion channel. CatSper is a core regulator of sperm tail calcium entry and sperm motility. All CatSper subunits are sperm specific proteins and are located in the principal piece of the sperm flagellum. The sperm specific CatSper channel controls the intracellular Ca(2+) concentration. Progesterone activates human CatSper, but not mouse, at low nanomolar concentrations by shifting the voltage dependency of the human CatSper channel into the physiological range. The pore of the CatSper channel is formed by four different CATSPER proteins (CATSPER 1, 2, 3, and -4) and all four are required for formation of the functional channel. In addition, three auxiliary subunits (CATSPERB, CATSPERG and CATSPERD) make this complex to be the one of the most sophisticated mammalian ion channels known. Only CATSPER1 is believed to be regulated by pH. The absence of any of the pore-forming CATSPER proteins, or gamma or beta auxiliary subunits- leads to disappearance of the whole CatSper channel. Syndromic male infertility (SMI) in association with CATSPER mutations is described in a number of human gene mutation studies. The absence of CatSper channel leads to male infertility both in mice and humans.
calcium ion transmembrane transporter activity of Activated CatSper Channel [plasma membrane]