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 CATSPER1 stability before intraflagellar transport and/or incorporation of the CatSper complex channel into the flagellar membrane. 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, TMEM249, TMEM262 and EFCAB9 (By similarity). HSPA1 may be an additional auxiliary complex member (By similarity). 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. 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 (By similarity). Specifically located in the principal piece of sperm tail. Belongs to the CATSPERD family. It is uncertain whether Met-1 or Met-5 is the initiator. In mouse, Slco6c1 is an additional auxiliary subunit of the CatSper complex. It is unclear if the related SLCO6A1 protein performs the same role in non-rodent species.