The function of CATSPERT (catsper channel auxiliary subunit tau, Ensembl gene identifier ENSG00000155754) is as follows. 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 CatSper complex targeting and trafficking into the quadrilinear nanodomains. Targets the preassembled CatSper complexes to elongating flagella, where it links the channel- carrying vesicles and motor proteins. .