Interactions between the tail and heads in 10S myosin. (A) Front view of reconstruction fitted with PDB ID 1I84 shows the interactions between tail segments 2 (magenta) and 3 (cyan) and the blocked head (TB2, TB3, TB4, TB5), between the two heads (BF), and between segment 2 and the other tail segments (the interaction extends upwards from TT1). TB2 is between the SH3 domain (blue) in the blocked head and segment 2, lying underneath. TB3 is between segment 2 and the converter domain (cyan) of the blocked head. TB4 is between segment 2 and the ELC (orange) of the blocked head. TB5 is between segment 3 and the blocked-head RLC. (B) Back view shows the interaction between the free head and the tail (TF1, TF2, TF3), between segments 1 and 3 (unresolved from each other) and the blocked head (TB1), and between tail segments 1 and 3 (starting at TT2). Interaction TF1 is between the actin-binding loop in the free head and the tail, while TF2 is between the free head upper 50K domain and the tail. TF3 may represent merging of tail and blocked head densities and not be a real interaction (see Results). TB1 is an extended interaction between the blocked head and segment 1 and/or segment 3. (C) Magnified view of TB5. Cys108 is represented by a cyan sphere. (D) The view in C is rotated 135° to visualize the geometric relationship between Cys108 and segment 3.