Nucleotide-dependent displacement and dynamics of the α-1 helix in kinesin revealed by site-directed spin labeling EPR

- Dipolar EPR detects the distance between the spin-labeled kinesin α-1 and α-2 helices.
- The distance has at least two populations: 1.5 nm (in crystal form: 20%) and >2.5 nm.
- The short distance conformer was populated 40% in the apo state with microtubules.
- ATP analog or ADP binding caused the 1.5 nm distance to be less populated (∼20%).
- The α-1 helix moves closer to the neck-linker (away from α-2) to facilitate docking.