Orientation and motion of myosin light chain and troponin in reconstituted muscle fibers as detected by ESR with a new bifunctional spin label.

摘要: Using electron spin resonance, we have studied dynamic structures of myosin neck domain and troponin C by site-directed labeling. We observed two broad but distinct orientations a label attached specifically to single cysteine (cys156) on the regulatoy light chain (RLC) in relaxed skeletal muscle fibers. The probe orientations, separated 25 degrees axial rotation, did not change upon activation, orientational distributions became narrower substantially, indicating that fraction heads undergoes disorder-to-order transition force generation contraction. These results provide insight into mechanism how move their domains translocate an actin filament. Site-directed spin-labeling was achieved residues human cardiac (TnC). Spin dipole-dipole interaction showed free TnC global structural (extended-to-compact) Ca2+ or Mg2+. spectra from labels at N-terminal half were almost identical parallel perpendicular fiber, suggesting molecule is flexible disoriented with respect filament axis. also succeeded, for first time, fixing newly-synthesized bifunctional rigidly solution (either +/- Ca2+), giving promise can determine precise coordinate principal axis protein surface.