Fig. 3: Structural changes during the power stroke.

a,b, Primed actomyosin structure (as shown in Fig. 1a; a) and the corresponding view of the postPS actomyosin structure (b) with lever positions indicated by a black arrow. The lever swings about 93° between structures. c,d, In the end-on view, primed actomyosin is observed to have an open actin-binding cleft (c), whereas postPS actomyosin has a closed cleft (d). e, In the top view, vectors depict the movement of myosin residue Cα atoms between primed and postPS actomyosin states. The biggest motions are attributable to lever swing, U50 rotation and binding to actin, and movement of the N-terminal domain. Schematic representations are shown of primed actomyosin in side view (to the left of f), end-on view towards the barbed end of F-actin (left of h) and end-on view towards the pointed end of F-actin (left of j), with dashed boxes illustrating the area of the structure highlighted in f and g, h and i, and j and k, respectively. f,g, The HCM loop and loop 4 are distant from the actin surface in the primed state (f) but interact with actin in the postPS state (g). The EM density is segmented and coloured by myosin subdomain (contour level 0.008). h,i, N-terminal actin interactions with loop 2 and helix W are changed between primed (h) and postPS (i) states. j,k, Nucleotide-binding site in primed (j) and postPS (k) structures. The EM density is segmented and coloured by myosin subdomain (contour level primed, 0.0085; postPS, 0.18). The backdoor (salt bridge between R219 and E442) is opened through rotation of the U50 and switch 1 and P-loop moving away from switch 2 (see Supplementary Video 3 and EM density maps). A DeepEMhancer post-processed map is depicted in a–d,f,g), and a RELION post-processed map is depicted in h–k.