In situ structure and rotary states of mitochondrial ATP synthase in whole <i>Polytomella</i> cells

Cells depend on a continuous supply of adenosine triphosphate (ATP), the universal energy currency. In mitochondria, ATP is produced by a series of redox reactions, whereby an electrochemical gradient is established across the inner mitochondrial membrane. The ATP synthase harnesses the energy of the gradient to generate ATP from adenosine diphosphate (ADP) and inorganic phosphate. We determined the structure of ATP synthase within mitochondria of the unicellular flagellate <i>Polytomella</i> by electron cryo-tomography and subtomogram averaging at up to 4.2-angstrom resolution, revealing six rotary positions of the central stalk, subclassified into 21 substates of the F₁ head. The <i>Polytomella</i> ATP synthase forms helical arrays with multiple adjacent rows defining the cristae ridges. The structure of ATP synthase under native operating conditions in the presence of a membrane potential represents a pivotal step toward the analysis of membrane protein complexes in situ.