Fig. 2. Structural details in the F₁ complex.

(A) Close-up views of the catalytic nucleotide binding sites in the β-subunits in cartoon representation. The maps for the nucleotide and phosphate are shown in mesh. (B) Structure of the F₁ complex in surface representation including the central stalk; subunits α_DP, β_DP*, and α_E removed to reveal how subunits γ and ε insert into the head. Inset: Close-up of the C-terminal extension of ε-subunit inserting between β_TP and α_DP* (not shown) showing the unwound turn of ε ¹²⁶AQL¹²⁸ (yellow) and the A. baumannii–specific C-terminal extension of ε. (C) Horizontal section of F₁ as indicated by the dashed line in (B) reveals mechanism of unidirectional inhibition. Steric clashes between ε and β_TP prevent rotation of the central stalk in the ATP hydrolysis direction (red cross) but permit unlocking and rotation in the ATP synthesis direction (yellow arrow).