Closing of the Nucleotide Pocket of Kinesin-Family Motors upon Binding to Microtubules

Abstract
We have used adenosine diphosphate analogs containing electron paramagnetic resonance (EPR) spin moieties and EPR spectroscopy to show that the nucleotide-binding site of kinesin-family motors closes when the motor·diphosphate complex binds to microtubules. Structural analyses demonstrate that a domain movement in the switch 1 region at the nucleotide site, homologous to domain movements in the switch 1 region in the G proteins [heterotrimeric guanine nucleotide–binding proteins], explains the EPR data. The switch movement primes the motor both for the free energy–yielding nucleotide hydrolysis reaction and for subsequent conformational changes that are crucial for the generation of force and directed motion along the microtubule.