Figure 1. Single-particle 3D reconstruction of C-zone reveals organization of titin, cMyBP-C, and myosin heads and tails (zoom for detail).

a, Cartoon of half thick filament, defining proximal, cMyBP-C-containing, and distal zones (P-, C- and D-zones, respectively), bare zone (BZ, lacking myosin heads), with central M-line, quasi-helical arrangement of myosin head pairs (colored spheres), with 430 Å repeat, and locations of cMyBP-C (pink) and titin (yellow, orange). b, 3D reconstruction of 5 crowns of heads, longitudinal surface view, showing IHMs forming 3 types of crown (Disordered/mobile, CrD, red; Tilted, CrT, blue; Horizontal, CrH, green—corresponding to crowns 2, 3, 1 of Tamborrini et al.¹⁹, shown in parentheses). One IHM is circled, with its two motor domains shown in different colors (light/dark green). Oriented with M-line at top. c, The 5-crown map in b after post-processing with DeepEMhancer, colored to identify myosin heavy chains (CrD, light/dark red; CrT, light/dark blue; CrH, light/dark green), coiled-coil myosin tails, and longitudinally arranged cMyBP-C molecules (pink) and 2 titin strands (yellow and orange); other colors in heads are light chains. d, Two-crown map (CrT and CrH) yields higher resolution, now revealing α-helices in the heads, better defining them in the tails, and revealing more detail in titin and cMyBP-C. e, Two-crown map viewed transversely at the level of CrH (36.6 Å slice), showing azimuthal and radial positions of components, and resolution of myosin tails into individual α-helices (dark and light color within each tail). f, Five-crown reconstruction (black silhouette) fitted with atomic models of myosin, cMyBP-C, and titin (ribbon depiction). g, Atomic model of portions of two sectors of reconstruction (defined as in ED Fig. 2), oriented to optimize visibility of all components. C (cMyBP-C), TA (titin A) and TB (titin B), with domains numbered; BH, FH, blocked and free heads; RLC, regulatory light chain; ELC, essential light chain. See also Supplementary Video 1.