Biophys J, April 2001, p. 1900-1904, Vol. 80, No. 4

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

Anne-Marie Lauzon,^* Patty M. Fagnant, David M. Warshaw, and Kathleen M. Trybus

 ^*Meakins-Christie Laboratories, McGill University Health Center, Montreal, Quebec H2X 2P2, Canada; and  Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont 05405 USA

Myosin II has two heads that are joined together by an -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 ± 0.6 nm for wild-type heavy meromyosin (WT HMM) to d = 0.1 ± 0.3 nm for the 0-hep zip construct (mean ± SE). Native values were restored in the 15-hep zip construct (d = 7.5 ± 0.7 nm). 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.

Biophys J, April 2001, p. 1900-1904, Vol. 80, No. 4
© 2001 by the Biophysical Society   0006-3495/01/04/1900/05  $2.00

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