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Biophys. J. BioFAST: First Published January 30, 2008. doi:10.1529/biophysj.107.122028
© 2008 by the Biophysical Society.

A more recent version of this article appeared on May 15, 2008.
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BIOPHYSICAL THEORY AND MODELING

The Elastic Properties of the Structurally Characterized Myosin II S2 Sub-domain: A Molecular Dynamics and Normal Mode Analysis

Ivana Adamovic 1, Srboljub M. Mijailovich 2 and Martin Karplus 1*

1 Harvard University
2 Harvard School of Public Health

* To whom correspondence should be addressed. E-mail: marci{at}tammy.harvard.edu.

Submitted on September 13, 2007
Revised on October 20, 2007
Accepted on 14 December 2007


  Abstract
The elastic properties (stretching and bending moduli) of myosin are expected to play an important role in its function. Of particular interest is the extended {alpha}-helical coiled-coil portion of the molecule. Since there is no high resolution structure for the entire coiled-coil, a study is made of the scallop myosin II S2 subdomain for which an X-ray structure is available (PDB 1nkn). We estimate the stretching and bending moduli of the S2 subdomain with an atomic level model by use of molecular simulations. The results were obtained by non-equilibrium molecular dynamics simulations in the presence of an external force, from the fluctuations in equilibrium molecular dynamics simulations and from normal modes. In addition, a poly-Ala (78 amino acid residues) {alpha}-helix model was examined to test the methodology, and because of its interest as part of the lever arm. As expected, both the {alpha}-helix and coiled-coil S2 subdomain are very stiff for stretching along the main axis, with the stretching stiffness constant in the range 60 - 80 pN/nm (scaled to the 60nm long S2). Both molecules are much more flexible for bending with a lateral stiffness of ~ 0.01pN/nm for S2 and 0.0055pN/nm for {alpha}-helix (scaled to the 60nm). These results are expected to be useful in estimating cross-bridge elasticity, which is required for understanding the strain-dependent transitions in the actomyosin cycle and for the development of three-dimensional models of muscle contraction.

Key Words: S2 subfragment, alpha-helix, coiled-coli, lateral stiffness, stretching stiffness




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Copyright © 2008 by the Biophysical Society.