Auxiliary component of the CatSper complex, a complex involved in sperm cell hyperactivation (PubMed:28226241, PubMed:34225353). Sperm cell hyperactivation is needed for sperm motility which is essential late in the preparation of sperm for fertilization (PubMed:28226241). 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, PubMed:34998468). 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 (PubMed:34998468). Specifically located in the principal piece of sperm tail. Testis-specific. Belongs to the CATSPERD family.