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. 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, CATSPERG, CATSPERD, CATSPERE, CATSPERZ, C2CD6/CATSPERT, SLCO6C1, TMEM249, TMEM262 and EFCAB9. HSPA1 may be an additional auxiliary complex member. The core complex members CATSPER1, CATSPER2, CATSPER3 and CATSPER4 form a heterotetrameric channel. The auxiliary CATSPERB, CATSPERG, 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. SLCO6C1 interacts with CATSPERE and TMEM262/CATSPERH interacts with CATSPERB, further stabilizing the complex. C2CD6/CATSPERT interacts at least with CATSPERD and is required for targeting the CatSper complex in the flagellar membrane. Specifically located in the principal piece of the sperm tail. Expressed in cauda sperm (at protein level). Expressed in cauda sperm (at protein level). Mutant mice have no gross abnormality in survival, appearance or behavior. Males are infertile with defective sperm hyperactivation. Females have normal reproductive ability and give birth with no difference in litter size.