Reconciling the working strokes of a single head of skeletal muscle myosin estimated from laser-trap experiments and crystal structures

• DOI: 10.1073/pnas.0506272103
• Publication Date: 2006-01-21T01:33:19Z
• Authors: John Sleep; Alexandre Lewalle; David Smith
• Keywords: Stroke

Myosin generates force by a rotation of its lever arm. Crystal structures myosin II indicate an unloaded working stroke 10–12 nm, range confirmed recent x-ray interference experiments. However, when actin filament, held between two weakly, optically trapped beads is made to interact with single head skeletal myosin, the bead displacements have often been reported as having mean value 5–6 that commonly interpreted stroke. In general, observed displacement not expected be equal because kinetics necessarily strain-dependent: this effect biases frequency binding events different sites so smaller than are preferentially selected. Our analysis tailored current trap experiments, in which time resolution insufficient detect prerigor states. If preceding transitions equilibrium, zero, contrary observations presence ATP. under ATP-cycling conditions, we find deflated 0.3–0.7 true stroke, depending on equilibrium constant and rate at first product state can detach from actin. The primary processive motors measured optical trapping similarly uncertain.