Figure 2.

Model of the kinesin mechanochemical cycle. (A Left) A schematic diagram illustrating how force affects the transition rates involving motion. The application of load tilts the energy landscape (shown as a contour plot) along the direction of loading, changing the passage rate over the barrier according to the relation shown, where F⃗ ⋅ δ⃗_i is the dot product of the force vector, F⃗, and the vector from the starting to the transition state, δ⃗_i, pointing along the reaction coordinate. (A Right) Rate constants derived from a global fit of this reaction scheme to the data of Figs. 3 and 4 (see Materials and Methods). (B) A hypothetical five-state reaction scheme in which the transitions from 1→4 (blue rectangle) contribute to the MM parameter k_b, whereas the transitions from 2→1 (red rectangle) contribute to k_cat. The transition from 2↔3 involves a relatively large motion along the microtubule, whereas transitions from 4→5 and 5→1 involve smaller motions perpendicular to the microtubule that are equal in magnitude and opposite in direction.