title: Orientation and structure of the Ndc80 complex on the microtubule lattice.
abstract: The four-subunit Ndc80 complex, comprised of Ndc80/Nuf2 and Spc24/Spc25 dimers, directly connects kinetochores to spindle microtubules. The complex is anchored to the kinetochore at the Spc24/25 end, and the Ndc80/Nuf2 dimer projects outward to bind to microtubules. Here, we use cryoelectron microscopy and helical image analysis to visualize the interaction of the Ndc80/Nuf2 dimer with microtubules. Our results, when combined with crystallography data, suggest that the globular domain of the Ndc80 subunit binds strongly at the interface between tubulin dimers and weakly at the adjacent intradimer interface along the protofilament axis. Such a binding mode, in which the Ndc80 complex interacts with sequential alpha/beta-tubulin heterodimers, may be important for stabilizing kinetochore-bound microtubules. Additionally, we define the binding of the Ndc80 complex relative to microtubule polarity, which reveals that the microtubule interaction surface is at a considerable distance from the opposite kinetochore-anchored end; this binding geometry may facilitate polymerization and depolymerization at kinetochore-attached microtubule ends.
authors.affiliation: Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Wilson-Kubalek
authors.forename: Iain M
authors.initials: IM
authors.lastname: Cheeseman
authors.forename: Craig
authors.initials: C
authors.lastname: Yoshioka
authors.forename: Arshad
authors.initials: A
authors.lastname: Desai
authors.forename: Ronald A
authors.initials: RA
authors.lastname: Milligan
mesh_terms: D018797:Cell Cycle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020285:Cryoelectron Microscopy; D018360:Crystallography, X-Ray; D003598:Cytoskeletal Proteins; D019281:Dimerization; D006801:Humans; D018386:Kinetochores / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism* / Q000648:ultrastructure; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D008941:Spindle Apparatus / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; C120529:NDC80 protein, human; C490197:NUF2 protein, human; D009687:Nuclear Proteins; D021122:Protein Subunits
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