Coiled-coil unwinding at the smooth muscle myosin head-rod junction is required for optimal mechanical performance.
Myosin II has two heads that are joined together by an alpha-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.
Lauzon
A M
AM
Meakins-Christie Laboratories, McGill University Health Center, Montreal, Quebec H2X 2P2, Canada.
Fagnant
P M
PM
Warshaw
D M
DM
Trybus
K M
KM
D000818:Animals; D002460:Cell Line; D007313:Insecta; D016350:Leucine Zippers; D009130:Muscle, Smooth / Q000737:chemistry*; D009218:Myosins / Q000737:chemistry*; D011487:Protein Conformation; D013997:Time Factors
D009218:Myosins