ATPase, subunit C of Fo/Vo complex is the main transmembrane subunit of V-type, A-type and F-type ATP synthases. ATPases are membrane-bound enzyme complexes/ion transporters that combine ATP synthesis and/or hydrolysis with the transport of protons across a membrane. ATPases can harness the energy from a proton gradient, using the flux of ions across the membrane via the ATPase proton channel to drive the synthesis of ATP. Some ATPases work in reverse, using the energy from the hydrolysis of ATP to create a proton gradient. There are different types of ATPases, which can differ in function, structure and in the type of ions they transport.
V-ATPase are primarily found in eukaryotic vacuoles, catalysing ATP hydrolysis to transport solutes and lower pH in organelles.
A-ATPases are found in Archaea and function like F-ATPases.
P-ATPases are found in bacteria and in eukaryotic plasma membranes and organelles, and function to transport a variety of different ions across membranes.
E-ATPases are cell-surface enzymes that hydrolyse a range of NTPs, including extracellular ATP.
The F-ATPases and V-ATPases are each composed of two linked complexes: the F1 or V1 complex contains the catalytic core that synthesizes/hydrolyses ATP, and the Fo or Vo complex that forms the membrane-spanning pore. The F- and V-ATPases all contain rotary motors, one that drives proton translocation across the membrane and one that drives ATP synthesis/hydrolysis. Subunit C was found in the Fo or Vo complex of F- and V-ATPases, respectively. In F-ATPases, ten C subunits form an oligomeric ring that makes up the Fo rotor. The flux of protons through the ATPase channel drives the rotation of the C subunit ring, which in turn is coupled to the rotation of the F1 complex gamma subunit rotor due to the permanent binding between the gamma and epsilon subunits of F1 and the C subunit ring of Fo. The sequential protonation and deprotonation of Asp61 of subunit C is coupled to the stepwise movement of the rotor. In V-ATPases, there are three proteolipid subunits that form part of the proton-conducting pore, each containing a buried glutamic acid residue that is essential for proton transport, and together they form a hexameric ring spanning the membrane. In a recent study c-subunit has been indicated as a critical component of the mitochondrial permeability transition pore.
