Single-molecule measurement of the stiffness of the rigor myosin head

Biophys J. 2008 Mar 15;94(6):2160-9. doi: 10.1529/biophysj.107.119396. Epub 2007 Dec 7.


The force-extension curve of single myosin subfragment-1 molecules, interacting in the rigor state with an actin filament, has been investigated at low [ATP] by applying a slow triangle-wave movement to the optical traps holding a bead-actin-bead dumbbell. In combination with a measurement of the overall stiffness of the dumbbell, this allowed characterization of the three extensible elements, the actin-bead links and the myosin. Simultaneously, another method, based on an analysis of bead position covariance, gave satisfactory agreement. The mean covariance-based estimate for the myosin stiffness was 1.79 pN/nm (SD = 0.7 pN/nm; SE = 0.06 pN/nm (n = 166 myosin molecules)), consistent with a recent report (1.7 pN/nm) from rabbit muscle fibers. In the triangle-wave protocol, the motion of the trapped beads during interactions was linear within experimental error over the physiological range of force applied to myosin (+/-10 pN), consistent with a Hookean model; any nonlinear terms could not be characterized. Bound states subjected to forces that resisted the working stroke (i.e., positive forces) detached at a significantly lower force than when subjected to negative forces, which is indicative of a strain-dependent dissociation rate.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin Cytoskeleton / metabolism
  • Actins / chemistry
  • Actomyosin / chemistry
  • Adenosine Triphosphate / chemistry
  • Animals
  • Biophysics / methods*
  • Muscle Contraction
  • Muscle Fibers, Skeletal / metabolism
  • Muscle Rigidity
  • Muscles / metabolism
  • Myosin Subfragments / chemistry
  • Myosins / chemistry*
  • Protein Conformation
  • Rabbits
  • Thermodynamics


  • Actins
  • Myosin Subfragments
  • Adenosine Triphosphate
  • Actomyosin
  • Myosins