CatSper4, is a protein which in humans is encoded by the CATSPER4 gene.   CatSper1 is a member of the  cation channels of sperm family of protein. The four proteins in this family together form a Ca-permeant 2+ ion channel specific essential for the correct function of sperm cells.
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"CatSper and Two-Pore Channels: Introduction". IUPHAR Database of Receptors and Ion Channels. International Union of Basic and Clinical Pharmacology.