title: The beginning of kinesin's force-generating cycle visualized at 9-A resolution.
abstract: We have used cryo-electron microscopy of kinesin-decorated microtubules to resolve the structure of the motor protein kinesin's crucial nucleotide response elements, switch I and the switch II helix, in kinesin's poorly understood nucleotide-free state. Both of the switch elements undergo conformational change relative to the microtubule-free state. The changes in switch I suggest a role for it in "ejecting" adenosine diphosphate when kinesin initially binds to the microtubule. The switch II helix has an N-terminal extension, apparently stabilized by conserved microtubule contacts, implying a microtubule activation mechanism that could convey the state of the bound nucleotide to kinesin's putative force-delivering element (the "neck linker"). In deriving this structure, we have adapted an image-processing technique, single-particle reconstruction, for analyzing decorated microtubules. The resulting reconstruction visualizes the asymmetric seam present in native, 13-protofilament microtubules, and this method will provide an avenue to higher-resolution characterization of a variety of microtubule- binding proteins, as well as the microtubule itself.
authors.affiliation: Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Charles V
authors.initials: CV
authors.lastname: Sindelar
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Downing
mesh_terms: D000244:Adenosine Diphosphate / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D020285:Cryoelectron Microscopy; D006801:Humans; D007091:Image Processing, Computer-Assisted; D016547:Kinesins / Q000737:chemistry* / Q000378:metabolism; D008870:Microtubules / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D011485:Protein Binding / Q000502:physiology; D017433:Protein Structure, Secondary
chemical_list: D046912:Multiprotein Complexes; D000244:Adenosine Diphosphate; D016547:Kinesins