Distinguishing inchworm and hand-over-hand processive kinesin movement by neck rotation measurements |
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Authors: | Hua Wei Chung Johnson Gelles Jeff |
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Affiliation: | Biophysics and Structural Biology Program, Biochemistry Department, Brandeis University, Waltham, MA 02454-9110, USA. |
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Abstract: | The motor enzyme kinesin makes hundreds of unidirectional 8-nanometer steps without detaching from or freely sliding along the microtubule on which it moves. We investigated the kinesin stepping mechanism by immobilizing a Drosophila kinesin derivative through the carboxyl-terminal end of the neck coiled-coil domain and measuring orientations of microtubules moved by single enzyme molecules at submicromolar adenosine triphosphate concentrations. The kinesin-mediated microtubule-surface linkage was sufficiently torsionally stiff (>/=2.0 +/- 0.9 x 10(-20) Newton meters per radian2) that stepping by the hypothesized symmetric hand-over-hand mechanism would produce 180 degree 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. |
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