Rat brain kinesin is a conventional kinesin that uses the energy from ATP hydrolysis to walk along the microtubule progressively. Studying how the chemical energy in ATP is utilized for mechanical movement is important to understand this moving function. The monomeric motor domain, rK354, was crystallized. An ATP analog, AMPPNP, was soaked in the active site. Comparing the complex structure of rK354×AMPPNP and that of rK354×ADP, a hypothesis is proposed that Glu237 in the Switch Ⅱ region sensors the presence of g-phosphate and transfers the signal to the microtubule binding region.