Extended Data Figure 4. Comparisons of IHM pseudo-atomic models, free- and blocked-heads and the SAH-domain character of start of segment-1.

a-f, Comparison of pseudo-atomic models of the IHM with LCs omitted to allow comparison of LCD heavy-chain structure. a, Pseudo-atomic model of SmM from the present study. b, Model (PDB id 1I84) produced from SmM heavy meromyosin IHM 2D crystal 20Å map⁷; tentative assignment of tail omitted. c, Model (PDB id 3JBH) produced from IHM of tarantula thick filament 20Å map⁴⁰, fitted with tarantula sequence. d, Model (PDB id 5TBY) proposed for human cardiac IHM by homology modelling the cardiac amino acid sequences on the tarantula model¹⁴. e, Model (downloaded from Spudich lab website as MS01.pdb) of human cardiac myosin IHM (produced by use of homology models fitted to tarantula IHM model 3DTP¹⁵). f, Model (downloaded as Supplementary Data 2) for cardiac IHM produced by use of a cardiac motor domain-ELC crystal structure (5N69) and homology model of RLC fitted into the tarantula thick filament IHM 20Å map³¹. g, Superposition of free- and blocked-head motors (up until pliant region) showing how the LCD regions differ between the heads (without light chains shown), segmented maps and model for motor domains shown. h, Blocked-head motor, model in map, i morph between blocked-head and free-head model and maps (shown without light chains), j Free-head model in map. Map contour level 0.28 (Supplementary Video 3). k, SmM heavy-chain sequence at the start of the predicted coiled coil. Coiled-coil seam a and d residues marked by grey stripes; acidic residues red, basic residues blue. i, Heptad net projection of sequence ³⁵ in which the dashed line shows the path of the polypeptide backbone as α-helix, circles and squares indicate the a and d positions of the heptad repeat and every seventh residue is repeated (in brackets) to allow all ionic interactions to be mapped.