FIGURE 1.

Chloroplast ATP synthase. A, current model using the x-ray structures of α₃β₃ (PDB code 1KMH) (67) and c₁₄-ring (PDB code 2W5J) (7). Protons flow from the p-side (lumen) through subunit a to the n-side (stroma) and drive the rotation of subunits c₁₄γϵ. This rotation induces ATP synthesis in the β subunits. Subunits b and b′ provide a stator stalk between subunits a and α₃β₃δ. B, top view; C, front view; D, side view depicting the water channel found in the MD simulation of the 13protonated system. Blue, water density at a contour level of 50 waters/ų during the course of the simulation. Green, backbone of c₁₄-ring. Red, oxygen atoms of conserved Glu⁶¹. The lipid bilayer is omitted for clarity. A, C, and D, top, n-side, and bottom, p-side.