Measurement of electrostatic interaction between actin and tropomyosin along thin filaments. (A and B) Electrostatic interaction energy between individual tropomyosin residues and actin residues 326 and 328 were plotted for atomic models of C- and B-state filaments (A; PDB IDs 7UTI and 7UTL) and for data taken from MD simulations carried out on the models and then energies averaged over 120 ns of the procedure (B). The peaks observed in these plots pinpoint salt bridges between actin and tropomyosin and the magnitude of the peaks indicates the corresponding strength of the interactions. Note that the same set of closely neighboring residues are involved in salt-bridge interactions in the B- and C-state filaments, and that this pattern persists during MD. The residue pairs involved are numbered.