The structure of an ATP-bound kinesin motor domain is predicted and conformational differences relative to the known ADP-bound form of the protein are identified. The differences should be attributed to force- producing ATP hydrolysis. Candidate ATP-kinesin structures were obtained by simulated annealing, by placement of the ATP γ-phosphate in the crystal structure of ADP-kinesin, and by interatomic distance constraints. The choice of such constraints was based on mutagenesis experiments, which identified Gly-234 as one of the γ-phosphate sensing residues, as well as on structural comparison of kinesin with the homologous nonclaret disjunctional (ncd) motor and with G-proteins. The prediction of nucleotide-dependent conformational differences reveals an allosteric coupling between the nucleotide pocket and the microtubule binding site of kinesin. Interactions of ATP with Gly-234 and Ser-202 trigger structural changes in the motor domain, the nucleotide acting as an allosteric modifier of kinesin's microtubule-binding state. We suggest that in the presence of ATP kinesin's putative microtubule binding regions L8, L12, L11, α4, α5, and α6 form a face complementary in shape to the microtubule surface; in the presence of ADP, the microtubule binding face adopts a more convex shape relative to the ATP-bound form, reducing kinesin's affinity to the microtubule.
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