Mechanical properties of myosin probed with the Photonic Force Microscope

To characterize mechanical properties like elasticity and length of different structural elements of myosin molecules we used a Photonic Force Microscope to observe the three dimensional thermal fluctuations of a microsphere attached to a single myosin molecule. By removing MgATP the myosin molecule was bound to an actin filament immobilized on a glass surface. Elastic properties of the linking molecule were derived from the probability distributions of the bead position using Boltzmann´s law. When freshly extracted full length striated muscle myosin molecules were used we found a molecular elasticity of about 0.03 pN/nm along the axis of the linking myosin molecule. In addition to the linker elasticity we also could determine the length of the linker between the observed microshere and the actin filament on the glass surface. For the full length myosin molecules the linker length was estimated to be about 100 nm. The stiffness observed here is very much lower than that derived for the myosin head domain by other approaches suggesting that it is dominated by a structural element outside the myosin head domain. To identify the structural correlate of the observed flexibility we make use of myosin constructs with a variety of different structural elements.