Force generation by recombinant myosin heads trapped between two functionalized surfaces

Fluorescence resonance energy transfer measurements have revealed that the lever-arm domain of myosin swings when it hydrolyzes Mg-ATP. It is generally accepted that this swing of the lever arm of myosin is the molecular basis of force generation. On the other hand, the possibility that the force might be generated at the interface between actin and myosin cannot be ignored. However, there is a third possibility, namely, that myosin itself generates force without actin. Thus, using recombinant subfragment 1 molecules of Dictyostelium myosin II that were trapped between two functionalized surfaces of a surface-force apparatus, we determined whether myosin itself could actually generate force. Here, we report that, despite the absence of actin, myosin heads themselves have a capacity to generate a force (at least approximately 0.2 pN/molecule) that is coupled to the structural changes. Although the role of actin should not be neglected because muscle physiologically shortens as a result of the interaction between actin and myosin, in this work the focus is on the question of whether the catalytic domain of myosin has the capacity to generate force.