Coiled-Coil Unwinding at the Smooth Muscle Myosin Head-Rod Junction Is Required for Optimal Mechanical Performance

AbstractMyosin II has two heads that are joined together by an α-helical coiled-coil rod, which can separate in the region adjacent to the head-rod junction (Trybus, K. M. 1994. J. Biol. Chem. 269:20819–20822). To test whether this flexibility at the head-rod junction is important for the mechanical performance of myosin, we used the optical trap to measure the unitary displacements of heavy meromyosin constructs in which a stable coiled-coil sequence derived from the leucine zipper was introduced into the myosin rod. The zipper was positioned either immediately after the heads (0-hep zip) or following 15 heptads of native sequence (15-hep zip). The unitary displacement (d) decreased from d=9.7±0.6nm for wild-type heavy meromyosin (WT HMM) to d=0.1±0.3nm for the 0-hep zip construct (mean±SE). Native values were restored in the 15-hep zip construct (d=7.5±0.7nm). We conclude that flexibility at the myosin head-rod junction, which is provided by an unstable coiled-coil region, is essential for optimal mechanical performance