part of proton-transporting V-type ATPase complex proton-transporting two-sector ATPase complex, proton-transporting domain proton-transporting V-type ATPase, V0 domain GO:0033179 cellular_component A protein complex that forms part of a proton-transporting V-type ATPase and mediates proton transport across a membrane. The V0 complex consists of at least four different subunits (a,c,d and e); six or more c subunits form a proton-binding rotor ring.