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On the Origin of Kinesin Limping Adrian N. Fehr,

Summary: On the Origin of Kinesin Limping
Adrian N. Fehr,
Braulio Gutie´rrez-Medina,
Charles L. Asbury,§
and Steven M. Block

Departments of Applied Physics and
Biology, Stanford University, Stanford, California, and §
Department of Physiology and Biophysics,
University of Washington, Seattle, Washington
ABSTRACT Kinesin is a dimeric motor with twin catalytic heads joined to a common stalk. Kinesin molecules move proces-
sively along microtubules in a hand-over-hand walk, with the two heads advancing alternately. Recombinant kinesin constructs
with short stalks have been found to ``limp'', i.e., exhibit alternation in the dwell times of successive steps. Limping behavior
implies that the molecular rearrangements underlying even- and odd-numbered steps must differ, but the mechanism by which
such rearrangements lead to limping remains unsolved. Here, we used an optical force clamp to measure individual, recombinant
dimers and test candidate explanations for limping. Introducing a covalent cross-link into the stalk region near the heads had no
effect on limping, ruling out possible stalk misregistration during coiled-coil formation as a cause. Limping was equally unaffected
by mutations that produced 50-fold changes in stalk stiffness, ruling out models where limping arises from an asymmetry in
torsional strain. However, limping was enhanced by perturbations that increased the vertical component of load on the motor,


Source: Asbury, Chip - Department of Physiology and Biophysics, University of Washington at Seattle


Collections: Biology and Medicine