Figure 6. Schematic of conformational and chemical states of dimeric kinesins.
(A) Model for the conformational and chemical states of dimeric kinesins with ADP•AlFx in our sample. State 1 corresponds to kinesin dimer in the two-head-bound state. State 2 corresponds to a highly transient state where the leading head detaches from the microtubule but the neck linker of the trailing head remains docked. This state transitions into state 3, driven by the entropy gain from a bigger space that the tethered head can explore once neck linker of the trailing head is undocked. State 3 corresponds to the singly-bound head. (B) Model for three key states in the regular motility cycle of dimeric kinesin with ATP. In state 1, after Pi releases, the trailing head (bound with ADP) has low affinity for the microtubule. After ATP binding in the leading head, the kinesin dimer enters a transitional state 2, where the nucleotide cleft is closed in the microtubule-bound head, but its neck linker is undocked. This state can be modeled by the singly-bound head. After ATP hydrolysis, the tethered head completes forward stepping, as seen in state 3. This state can be modeled by our two-head-bound kinesin dimer.