Microtubule cross-linking triggers the directional motility of kinesin-5.
Although assembly of the mitotic spindle is known to be a precisely controlled process, regulation of the key motor proteins involved remains poorly understood. In eukaryotes, homotetrameric kinesin-5 motors are required for bipolar spindle formation. Eg5, the vertebrate kinesin-5, has two modes of motion: an adenosine triphosphate (ATP)-dependent directional mode and a diffusive mode that does not require ATP hydrolysis. We use single-molecule experiments to examine how the switching between these modes is controlled. We find that Eg5 diffuses along individual microtubules without detectable directional bias at close to physiological ionic strength. Eg5's motility becomes directional when bound between two microtubules. Such activation through binding cargo, which, for Eg5, is a second microtubule, is analogous to known mechanisms for other kinesins. In the spindle, this might allow Eg5 to diffuse on single microtubules without hydrolyzing ATP until the motor is activated by binding to another microtubule. This mechanism would increase energy and filament cross-linking efficiency.
Kapitein
Lukas C
LC
Department of Physics and Astronomy, Vrije Universiteit, 1081 HV Amsterdam, Netherlands.
Kwok
Benjamin H
BH
Weinger
Joshua S
JS
Schmidt
Christoph F
CF
Kapoor
Tarun M
TM
Peterman
Erwin J G
EJ
D000818:Animals; D004058:Diffusion; D019281:Dimerization; D049452:Green Fluorescent Proteins / Q000378:metabolism; D016547:Kinesins / Q000737:chemistry / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism*; D009994:Osmolar Concentration; D020836:Protein Structure, Quaternary; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013552:Swine; D014981:Xenopus; D029867:Xenopus Proteins / Q000737:chemistry / Q000378:metabolism*
C088335:KIF11 protein, Xenopus; D011993:Recombinant Fusion Proteins; D029867:Xenopus Proteins; D049452:Green Fluorescent Proteins; D016547:Kinesins