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Published online 27 November 2000. doi:10.1083/jcb.151.5.1093
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© The Rockefeller University Press, 0021-9525/2000//1093 $5.00
The Journal of Cell Biology, Volume 151, Number 5, , 2000 1093-1100

Original Article

Engineering the Processive Run Length of the Kinesin Motor



Kurt S. Thorna,b, Jeffrey A. Ubersaxa, and Ronald D. Valea,c

a Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California 94143
b Graduate Group in Biophysics, University of California, San Francisco, California 94143
c The Howard Hughes Medical Institute, University of California, San Francisco, California 94143
Dept. of Cellular and Molecular Pharmacology, 513 Parnassus Ave., University of California, San Francisco, CA 94143.415-502-1391415-476-6380

Conventional kinesin is a highly processive molecular motor that takes several hundred steps per encounter with a microtubule. Processive motility is believed to result from the coordinated, hand-over-hand motion of the two heads of the kinesin dimer, but the specific factors that determine kinesin's run length (distance traveled per microtubule encounter) are not known. Here, we show that the neck coiled-coil, a structure adjacent to the motor domain, plays an important role in governing the run length. By adding positive charge to the neck coiled-coil, we have created ultra-processive kinesin mutants that have fourfold longer run lengths than the wild-type motor, but that have normal ATPase activity and motor velocity. Conversely, adding negative charge on the neck coiled-coil decreases the run length. The gain in processivity can be suppressed by either proteolytic cleavage of tubulin's negatively charged COOH terminus or by high salt concentrations. Therefore, modulation of processivity by the neck coiled-coil appears to involve an electrostatic tethering interaction with the COOH terminus of tubulin. The ability to readily increase kinesin processivity by mutation, taken together with the strong sequence conservation of the neck coiled-coil, suggests that evolutionary pressures may limit kinesin's run length to optimize its in vivo function.

Key Words: kinesin • tubulin • single-molecule motility • processivity • molecular motors

© 2000 The Rockefeller University Press

Abbreviations used in this paper: GFP, green fluorescent protein; QPD, quadrant photodiode.


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