Snapshots of a rotary pump Vesicular- or vacuolar-type adenosine triphosphatases (V-ATPases) are ATP-hydrolysis–driven proton pumps. In neurons, V-ATPase activity generates a proton gradient across the membrane of synaptic vesicles so that neurotransmitters can be loaded into the vesicles. Abbas et al. developed a method to purify V-ATPase from rat brain and determined the structure of the entire complex by cryo–electron microscopy. Native mass spectrometry showed that the preparation was homogeneous and complemented structural studies by confirming the subunit composition. Three rotational states were resolved at better than 4-angstrom resolution, providing insight into the conformational changes that couple ATP hydrolysis to proton pumping. Science , this issue p. 1240