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 α-​helical coiled-​coil portion of the mol. Since there is no high resoln. 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 (Protein Data Bank 1nkn)​. The authors est. the stretching and bending moduli of the S2 subdomain with an at. level model by use of mol. simulations. Results were obtained from nonequil. mol. dynamics simulations in the presence of an external force, from the fluctuations in equil. mol. dynamics simulations and from normal modes. In addn., a poly-​Ala (78 amino acid residues) α-​helix model was examd. to test the methodol. and because of its interest as part of the lever arm. As expected, both the α-​helix and coiled-​coil S2 subdomain are very stiff for stretching along the main axis, with the stretching stiffness const. in the range 60-​80 pN​/nm (scaled to the 60 nm long S2)​. Both mols. are much more flexible for bending with a lateral stiffness of ∼0.010pN​/nm for the S2 and 0.0055pN​/nm for the α-​helix (scaled to 60 nm)​. These results are expected to be useful in estg. 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.