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Distinguishing Inchworm and Hand-Over-Hand Processive Kinesin Movement by Neck Rotation Measurements
Wei Hua,1Johnson Chung,2Jeff Gelles12*
The motor enzyme kinesin makes hundreds of unidirectional
8-nanometer steps without detaching from or freely sliding alongthe
microtubule on which it moves. We investigated the kinesinstepping
mechanism by immobilizing a Drosophila kinesin derivativethrough the carboxyl-terminal end of the neck coiled-coil domainand
measuring orientations of microtubules moved by single enzymemolecules
at submicromolar adenosine triphosphate concentrations.The
kinesin-mediated microtubule-surface linkage was sufficientlytorsionally stiff (2.0 ± 0.9 × 1020 Newton
meters per radian2) that stepping by the hypothesized
symmetric hand-over-hand mechanismwould produce 180° rotations of
the microtubule relative to theimmobilized kinesin neck. In fact,
there were no rotations, afinding that is inconsistent with symmetric
hand-over-hand movement.An alternative "inchworm" mechanism is
consistent with our experimentalresults.
1 Biophysics and Structural Biology Program,
2 Biochemistry Department, Brandeis University,
Waltham, MA 02454-9110, USA.
*
To whom correspondence should be addressed. E-mail:
gelles{at}brandeis.edu
2.0 ± 0.9 × 10
20 Newton
meters per radian2) that stepping by the hypothesized
symmetric hand-over-hand mechanism would produce 180° rotations of
the microtubule relative to the immobilized kinesin neck. In fact,
there were no rotations, a finding that is inconsistent with symmetric
hand-over-hand movement. An alternative "inchworm" mechanism is
consistent with our experimental results.
