3D reconstruction and flexibility of the hybrid engine Acetobacterium woodii F-ATP synthase.

The Na-translocating FF ATP synthase from Acetobacterium woodii (AwF-ATP synthase) with a subunit stoichiometry of α:β:γ:δ:ε:a:b:(c):c represents an evolutionary path between ATP-synthases and vacuolar ATPases, by containing a heteromeric rotor c-ring, composed of subunits c, c and c, and an extra loop (γ) within the rotary γ subunit. Here, the recombinant AwF-ATP synthase was subjected to negative stain electron microscopy and single particle analysis. The reference free 2D class averages revealed high flexibility of the enzyme, wherein the F and F domains distinctively bended to adopt multiple conformations. Moreover, both the F and F domains tilted relative to each other to a maximum extent of 28° and 30°, respectively. The first 3D reconstruction of the AwF-ATP synthase was determined which accommodates well the modelled structure of the AwF-ATP synthase as well as the γ-loop. Molecular simulations of the enzyme underlined the bending features and flexibility observed in the electron micrographs, and enabled assessment of the dynamics of the extra γ-loop.