Molecular imaging of Escherichia coli F₀F₁-ATPase in reconstituted membranes using atomic force microscopy

The structure of Escherichia coli F₀F₁-ATPase (ATP synthase), and its F₀ sector reconstituted in lipid membranes was analyzed using atomic force microscopy (AFM) by tapping-mode operation. The majority of F₀F₁-ATPases were visualized as spheres with a calculated diameter of ~90 Å, and a height of ~ 100 Å from the membrane surface. F₀ sectors were visualized as two different ring-like structures (one with a central mass and the other with a central hollow of ≤18 Å depth) with a calculated outer diameter of ~ 130 Å. The two different images possibly represent the opposite orientations of the complex in the membranes. The ring-like projections of both images suggest inherently asymmetric assemblies of the subunits in the F₀ sector. Considering the stoichiometry of F₀ subunits, the area of the image observed is large enough to accommodate all three F₀ subunits in an asymmetric manner.