title: Force and premature binding of ADP can regulate the processivity of individual Eg5 dimers.
abstract: Using a high-resolution optical trapping instrument, we directly observed the processive motions of individual Eg5 dimers over a range of external loads and ATP, ADP, and phosphate concentrations. To constrain possible models for dissociation from the microtubule, we measured Eg5 run lengths and also compared the duration of the last step of a processive run to all previous step durations. We found that the application of large longitudinal forces in either hindering or assisting directions could induce Eg5-microtubule dissociation. At a constant moderate force, maintained with a force clamp, the premature binding of ADP strongly promoted microtubule release by Eg5, whereas the addition of ATP or phosphate had little effect on dissociation. These results imply that run length is determined not only by the load, but also by the concentration and type of nucleotides present, and therefore that the biochemical cycles of the two motor domains of the Eg5 dimer are coordinated to promote processive stepping.
authors.affiliation: Department of Mechanical Engineering, University of California, Santa Barbara, California, USA. valentine@engineering.ucsb.edu
authors.forename: Megan T
authors.initials: MT
authors.lastname: Valentine
authors.forename: Steven M
authors.initials: SM
authors.lastname: Block
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism* / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D006801:Humans; D016547:Kinesins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D008870:Microtubules / Q000378:metabolism; D009068:Movement / Q000187:drug effects*; D010710:Phosphates / Q000494:pharmacology; D011336:Probability; D011485:Protein Binding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary
chemical_list: C470243:KIF11 protein, human; D010710:Phosphates; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D016547:Kinesins