Subunit of the V0 complex of vacuolar(H+)-ATPase (V-ATPase), a multisubunit enzyme composed of a peripheral complex (V1) that hydrolyzes ATP and a membrane integral complex (V0) that translocates protons (PubMed:12963731). V-ATPase is responsible for acidifying a variety of intracellular compartments in eukaryotic cells, thus providing most of the energy required for transport processes in the vacuolar system (By similarity). May play a role in coupling of proton transport and ATP hydrolysis (PubMed:12963731). In aerobic conditions, involved in intracellular iron homeostasis, thus triggering the activity of Fe(2+) prolyl hydroxylase (PHD) enzymes, and leading to HIF1A hydroxylation and subsequent proteasomal degradation (By similarity). May play a role in cilium biogenesis through regulation of the transport and the localization of proteins to the cilium (By similarity). V-ATPase is a heteromultimeric enzyme made up of two complexes: the ATP-hydrolytic V1 complex and the proton translocation V0 complex (By similarity). The V1 complex consists of three catalytic AB heterodimers that form a heterohexamer, three peripheral stalks each consisting of EG heterodimers, one central rotor including subunits D and F, and the regulatory subunits C and H (By similarity). The proton translocation complex V0 consists of the proton transport subunit a, a ring of proteolipid subunits c9c'', rotary subunit d, subunits e and f, and the accessory subunits ATP6AP1/Ac45 and ATP6AP2/PRR (By similarity). Interacts with ATP6AP2; ATP6AP2 is a V-ATPase accessory protein and the interaction promotes v-ATPase complex assembly (By similarity). Interacts with TMEM9; TMEM9 is a v-ATPase assembly regulator and the interaction induces the interaction with ATP6AP2 (By similarity). Interacts with PIP4P1 (PubMed:29644770). Localizes to centrosome and the base of the cilium. Ubiquitous. Expressed throughout early development. Belongs to the V-ATPase V0D/AC39 subunit family.