title: A nonmotor microtubule binding site in kinesin-5 is required for filament crosslinking and sliding.
abstract: Kinesin-5, a widely conserved motor protein required for assembly of the bipolar mitotic spindle in eukaryotes, forms homotetramers with two pairs of motor domains positioned at opposite ends of a dumbbell-shaped molecule [1-3]. It has long been assumed that this configuration of motor domains is the basis of kinesin-5's ability to drive relative sliding of microtubules [2, 4, 5]. Recently, it was suggested that in addition to the N-terminal motor domain, kinesin-5 also has a nonmotor microtubule binding site in its C terminus [6]. However, it is not known how the nonmotor domain contributes to motor activity, or how a kinesin-5 tetramer utilizes a combination of four motor and four nonmotor microtubule binding sites for its microtubule organizing functions. Here we show, in single molecule assays, that kinesin-5 homotetramers require the nonmotor C terminus for crosslinking and relative sliding of two microtubules. Remarkably, this domain enhances kinesin-5's microtubule binding without substantially reducing motor activity. Our results suggest that tetramerization of kinesin-5's low-processivity motor domains is not sufficient for microtubule sliding because the motor domains alone are unlikely to maintain persistent microtubule crosslinks. Rather, kinesin-5 utilizes nonmotor microtubule binding sites to tune its microtubule attachment dynamics, enabling it to efficiently align and sort microtubules during metaphase spindle assembly and function.
authors.affiliation: Laboratory of Chemistry and Cell Biology, The Rockefeller University, New York, NY 10065, USA.
authors.forename: Joshua S
authors.initials: JS
authors.lastname: Weinger
authors.forename: Minhua
authors.initials: M
authors.lastname: Qiu
authors.forename: Ge
authors.initials: G
authors.lastname: Yang
authors.forename: Tarun M
authors.initials: TM
authors.lastname: Kapoor
mesh_terms: D000818:Animals; D001665:Binding Sites; D016547:Kinesins / Q000737:chemistry* / Q000378:metabolism*; D008870:Microtubules / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D029867:Xenopus Proteins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: C088335:KIF11 protein, Xenopus; D029867:Xenopus Proteins; D016547:Kinesins