Auxiliary component of the CatSper complex, a complex involved in sperm cell hyperactivation. Sperm cell hyperactivation is needed for sperm motility which is essential late in the preparation of sperm for fertilization. Required for a distribution of the CatSper complex in linear quadrilateral nanodomains along the flagellum, maximizing fertilization inside the mammalian female reproductive tract. Together with EFCAB9, associates with the CatSper channel pore and is required for the two-row structure of each single CatSper channel. . This is the function of Ensembl gene identifier ENSG00000219435 (CATSPERZ, catsper channel auxiliary subunit zeta).