Extended Data Fig. 4. Tracking myosin tails and their interactions (zoom for detail).

a, Transverse slices of reconstruction (looking towards M-line) showing the tail arrangement at crowns H, T, and D, respectively (colored lines in c) for TaH (green), TaT (blue) and TaD (red). Tails are tracked by showing their positions at different crown levels (numerals), using the convention devised by Squire^21,26, as they travel from their N-terminal origins, at the head-tail junction of each IHM (level 1), to their C-terminal tips (level 11). Black lines in colored sectors replace the numerals, revealing the quite different courses of the 3 tail types as they travel along the filament. For example, TaD lie near the surface while TaT are the most central, forming the filament core. Titins A and B are labeled TAn and TBn, where n is the n^th titin domain in the 430 Å repeat. MyBP-C is pink and labeled Cn (where n is the MyBP-C domain³⁰). The dotted black lines show one sector (colored) at each crown. Rectangles show examples of interactions of tails staggered by 1, 3, 5, and 7 crowns. Note sheets of CrD tails (red) staggered by 3 crowns (430 Å) near surface of backbone, forming a binding platform for cMyBP-C (see text). b, Cross-section at CrH, showing map (left) and corresponding space-filling atomic model (right), revealing clear examples of contact (thus interaction) between myosin tails with various staggers. Similar contacts are seen at other levels. c, longitudinal view of map (M-line at right) showing where slices in a are cut. d-f, Longitudinal views of reconstruction showing interactions of tails staggered by 1, 3, 5 or 7 crowns (~ 143, 430, 715 or 1,001 Å), as predicted by²³, corresponding to differences in tail numbers of 1, 3, 5, and 7 in a. Main sites of contact are inside the rectangular boxes. The most common sites are the distal LMM regions of each tail, including the ACD at the C-terminus (top boxes), consistent with its requirement for filament assembly (see text). The most prevalent stagger (3-crowns, 430 Å) is confined to homologous tails (TaH-TaH, TaT-TaT, TaD-TaD) (e). Heterologous tail combinations are staggered by 5 crowns (TaT-TaD, TaD-TaH) and one (TaH-TaD) by 7 crowns (f). One heterologous pair (TaH-TaT) exhibits a 141 Å stagger between S2s in the same sector (d, right) and between LMMs (including the ACD) from different sectors (d, left). g, Examples of charge interactions between S2’s staggered by 141 Å and LMMs by 430 Å (red, negative; blue, positive). h, Map and model at the 4 skip residues in CrH tails (Supplementary Fig. 3) and comparison of skip 1 in the filament (green) with corresponding crystal structure of skip 1 (PDB 4xa1, pink²⁴). The similarity gives support for the relevance of this X-ray model to the native structure. i, CrH, CrT and CrD tails with skip residues marked. All skips in the 3 tails appear to be associated with a longer coiled-coil pitch (~100–110 Å compared with regular ~75 Å) and with bends in the tail. Interestingly, the bends are not identical for all three tail types. Skip 1 of TaT and TaH shows a slight bend, while the TaD bend is sharper; skip 2 of TaT shows a slight bend, while TaD and TaH bends are sharp; skip 3 of all tails shows a mildly bent structure; and skip 4 bend is stronger in TaT and TaD than TaH. See also Supplementary Videos 2 and 3.