Fig. 2. Comparison of the three observed structural conformations of myosin. The structures are weak-binding states, but are modeled as complexed with actin for illustration. Motor domains (gray) and converter domains/lever arms (colored) for the myosin detached state (red) (scallop S1-ADP, PDB 1B7T) (Houdusse et al., 1999), near-rigor state (green) (nucleotide-free scallop S1, PDB 1DFK) (Houdusse et al., 2000) and transition state (cyan) (scallop S1-ADP·VO₄, PDB 1DFL) (Houdusse et al., 2000) are shown bound to a short actin filament of five molecules (yellow). In the detached state, the lever arm and associated light chains (not pictured) would collide with an extended actin filament. Motor domains were aligned using a least-squares alignment of 19 -carbon atoms, including residues 168-186.