Fig. 3.
Torque generation. (a) Residues involved in the γ-subunit, shown as colored spheres. (b) Torque distribution over the residues (residue number on the y axis) of the γ-stalk. Torque profiles during the 85° (Left) and 35° (Right) substep rotations, respectively (see text). To focus on the mechanical coupling mechanism, only the internetwork repulsion (Eq. 2) is included in determining the torque; torques that act in the opposite direction are not shown. The productive torque is scaled to lie between 0 and 1 on each map; the maximum torque on each map is scaled to 1. The torque (τ) is then colored based on a relative scale, τ < 0.1 (black), 0.1 ≤ τ < 0.2 (green), 0.2 ≤ τ < 0.3 (yellow), and τ ≥ 0.3 (red). Residue numbers (bMF1 numbering is used, and the corresponding yMF1 number is given below in parenthesis) of four torque generation “hot spot” clusters on the γ-stalk are labeled by using the same color scheme for identifying residues in a: γ:20–25 (20–25) (red), γ:75–79 (81–85) (dark blue), γ:232–238 (237–243) (green), and γ:252–258 (257–263) (cyan). A region on the β-subunit that is tightly coupled to the torque generation, in particular βE:390–391 (390–391), is shown as yellow spheres in a. The torque generation for the 85° substep rotation displays a relaying pattern, where the first set of torques is generated primarily on the N-terminal helix of the coiled-coil (γ:20–25) and the second set of torques is generated on the C-terminal helix (γ:232–238). The illustrations were made with the program VMD.