Function
pH-dependent Ca(2+) sensor required to activate the CatSper channel, a complex involved in sperm cell hyperactivation (PubMed:31056283). Sperm cell hyperactivation is needed for sperm motility which is essential late in the preparation of sperm for fertilization (PubMed:31056283). Associates with the CatSper complex via direct interaction with CATSPERZ, and senses intracellular Ca(2+) (PubMed:31056283). Together with CATSPERZ, associates with the CatSper channel pore and is required for the two-row structure of each single CatSper channel (PubMed:31056283).