MD-based steering of the 7G myosin mutant from its pre-powerstroke to its target post-powerstroke configuration triggers aberrant tropomyosin C-state to M-state movement. (A) The image illustrates the post-powerstroke position of the 7G model of myosin S1 on actin–tropomyosin following steering over a three-actin filament segment containing tropomyosin pseudorepeat 3. The layout and color scheme in Fig. 4 is the same as that for WT in Fig. 2 B, except that 7G-associated tropomyosin is colored dark green while corresponding WT tropomyosin (lighter green) is overlaid for comparison. The 3–5 Å azimuthal difference between the two tropomyosin strands is evident, namely tropomyosin in the mutant is closer to the tip of myosin Loop-4, and closer to the rest of S1 as well as to the outer domain of actin. (B and C) The proximity of 7G-S1 and tropomyosin results in hydrogen bond formation (solid black lines) between the outstretched 7G-S1 Loop 4 and tropomyosin during the pre- to post-powerstroke steering. For example, after 10 ns of simulation, hydrogen bonds form between tropomyosin Arg 101 and 7G-S1 Gly 369 and Gly 370 (B), while at 60 ns hydrogen bonds characterize tropomyosin Arg 90 connections to 7G-S1 Gly 369 and Gly 371 (C) (cf. Table 1). Such hydrogen bonding is absent in WT (not shown). (D and E) Comparison of transverse sections focused on the WT and 7G-S1-induced translocation of tropomyosin during pre- to post-powerstroke steering (respective pre- and post-powerstroke images overlaid). The sections show that WT tropomyosin movement involves both a rotation and an azimuthal translation on actin (D), while in the 7G case only azimuthal shifting occurs.