Rotary ATPases (F- and V-ATPases) are at the very centre of the energy metabolism of all life forms on our planet. They make use of a Mitchell proton motive force (pmf) generated by oxidative phosphorylation, photosynthetic light reactions or other processes to make ATP, or, in the reverse process, produce a pmf across the coupling membrane at the expense of ATP hydrolysis. Animal F-ATP synthase resides at the inner mitochondrial membrane, where it is synthesizing the majority of all ATP involved in physiological processes via the recycling of ATP from ADP and Pi. The structure of detergent solubilized, intact bovine F-ATP synthase has been studied by single particle electron cryo-microscopy to the resolution of ~20Å1 and numerous X-ray crystal structures of subcomplexes, which include the water soluble F1 domain2 , F1 in complex with a partial peripheral stalk3 and F1-c84 , have been reported. However, ways to examine the molecular structure of intact F-ATP synthase in its physiological environment of the lipid bilayer have thus far been limited.
We have succeeded to produce highly stable, crystalline tubes of intact mitochondrial F-ATP synthase isolated from bovine heart muscle. This made it possible to use electron cryo-tomography in combination with sub-tomogram averaging for the in vitro examination of the bovine F-ATP synthase's molecular structure in the membrane for the first time.