Auxiliary component of the CatSper complex, a complex involved in sperm cell hyperactivation (PubMed:28226241, PubMed:31056283, PubMed:34225353). Sperm cell hyperactivation is needed for sperm motility which is essential late in the preparation of sperm for fertilization (PubMed:28226241, PubMed:31056283). Required for a distribution of the CatSper complex in linear quadrilateral nanodomains along the flagellum, maximizing fertilization inside the mammalian female reproductive tract (PubMed:28226241). Together with EFCAB9, associates with the CatSper channel pore and is required for the two-row structure of each single CatSper channel (PubMed:31056283). Component of the CatSper complex or CatSpermasome composed of the core pore-forming members CATSPER1, CATSPER2, CATSPER3 and CATSPER4 as well as auxiliary members CATSPERB, CATSPERG2, CATSPERD, CATSPERE, CATSPERZ, C2CD6/CATSPERT, SLCO6C1, TMEM249, TMEM262 and EFCAB9 (PubMed:34225353, PubMed:28226241). HSPA1 may be an additional auxiliary complex member (By similarity). The core complex members CATSPER1, CATSPER2, CATSPER3 and CATSPER4 form a heterotetrameric channel (PubMed:34225353). The auxiliary CATSPERB, CATSPERG2, CATSPERD and CATSPERE subunits form a pavilion-like structure over the pore which stabilizes the complex through interactions with CATSPER4, CATSPER3, CATSPER1 and CATSPER2 respectively (PubMed:34225353). SLCO6C1 interacts with CATSPERE and TMEM262/CATSPERH interacts with CATSPERB, further stabilizing the complex (PubMed:34225353). C2CD6/CATSPERT interacts at least with CATSPERD and is required for targeting the CatSper complex in the flagellar membrane (Probable). Interacts with EFCAB9; the interaction is direct, Ca(2+)-dependent and connects EFCAB9 with the CatSper complex (PubMed:31056283). Dissociates from EFCAB9 at elevated pH (PubMed:31056283). Specifically located in the principal piece of sperm tail (PubMed:28226241). Although it does not contain a transmembrane domain, localizes with the CatSper complex at the flagellum membrane (PubMed:28226241). Testis-specific (PubMed:20339383, PubMed:28226241). Expressed in adult but not in fetal testis (PubMed:20339383). Not expressed in ovary. Within testis, expression is restricted to spermatids (PubMed:20339383). Mice are normal but males show severe male subfertility. Mutant males display fragmented patterns of CatSper complex stripes in the tails of their sperm, leading to a reduction of calcium ions that pass through the channels to enter the cell. As consequence, the sperm tail is more rigid, preventing it from moving efficiently within the female. Mutant sperm are less able to penetrate the egg than normal sperm.