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Probing the kinesin reaction cycle with a 2D optical force clamp

Summary: Probing the kinesin reaction cycle with a 2D optical
force clamp
Steven M. Block*
, Charles L. Asbury*, Joshua W. Shaevitz§
, and Matthew J. Lang*¶
Departments of *Biological Sciences, Applied Physics, and §Physics, Stanford University, Stanford, CA 94305
Edited by Charles F. Stevens, Salk Institute for Biological Studies, La Jolla, CA, and approved January 3, 2003 (received for review November 4, 2002)
With every step it takes, the kinesin motor undergoes a mechano-
chemical reaction cycle that includes the hydrolysis of one ATP
molecule, ADP Pi release, plus an unknown number of additional
transitions. Kinesin velocity depends on both the magnitude and
the direction of the applied load. Using specialized apparatus, we
subjected single kinesin molecules to forces in differing directions.
Sideways and forward loads up to 8 pN exert only a weak effect,
whereas comparable forces applied in the backward direction lead
to stall. This strong directional bias suggests that the primary
working stroke is closely aligned with the microtubule axis. Side-
ways loads slow the motor asymmetrically, but only at higher ATP
levels, revealing the presence of additional, load-dependent tran-
sitions late in the cycle. Fluctuation analysis shows that the cycle


Source: Asbury, Chip - Department of Physiology and Biophysics, University of Washington at Seattle
Block, Steven - Departments of Biological Sciences & Applied Physics, Stanford University
Lang, Matthew - Division of Biological Engineering & Department of Mechanical Engineering, Massachusetts Institute of Technology (MIT)


Collections: Biology and Medicine; Biotechnology; Engineering; Physics