Supplementary Movie Legends
Supplementary Movie 1
Movie of longitudinal view of reconstruction,including three complete crownsof heads, rotated around longitudinal axis(bare zone direction at top). Compare Fig. 1c of paper. Each crown contains fourJ-motifs separated by 90 degrees. The filament rotates 90 degrees, revealing all unique views,owing to the 4-fold rotational symmetry of the filament.
Supplementary Movie2
This movie helps interpretation of Fig. 2a of the paper. It first shows a longitudinal view of the reconstruction, including only a single crown of heads (see Supplementary Fig. 2). The crown rotates 90 degrees, then becomes truncated to include only a 14.5 nm repeat (slightly shorter than a crown, owing to motif overlap). This segment then rotates 90 degrees towards the viewer to show a transverse view from the direction of the bare zone, as seen in Fig. 2a of the paper. The motif originally located at the front of the reconstruction is now seen to be located at the bottom, whereas the motif originally hidden at the back of the reconstruction is now at the top. The segment now rotates 90 degrees around the filament axis to produce an identical view, illustrating the 4-fold rotational symmetry. Finally, the segment is rotated in three 30 degree steps to simulate the views obtained when moving by 14.5 nm steps along the filament axis away from the bare zone: the helical symmetry of the tarantula filament is such that each segment is rotated 30 degrees relative to the previous one (see Supplementary Movie 3).
Supplementary Movie3
This movie shows how portions of different crowns contribute toatransverse view of thereconstructioncontaining a single 14.5 nm repeat (cf. Fig. 2a of paper and Supplementary Movie 2). The 14.5 nm thick segment is initially positioned and orientedas in Fig. 2a, and then progressively moves away from the bare zone through two more repeats. The filament appears to rotate by 30 degrees for each 14.5 nm of movement along the filament axis (see Supplementary Movie 2). The initial and final positions of the segments are shown in Supplementary Fig. 2.
Supplementary Movie4
This movie provides a three-dimensional perspective on the fitting of the heads of the smooth muscle HMM space-filling atomic model (PDB1i843)into the J-motif of the tarantula thick filament 3D reconstruction (cf.Fig. 3a of paper). The filament is oriented with the bare zone at the top. The view moves from one side of the motif to the other around a vertical axis (cf. Fig. 1 of paper and Supplementary Movie 1). A rod-like region of density can be seen connecting the bottom of the “J” structure to the underlying surface of the filament core (red asterisk in Fig. 3a of paper). This is the proposed location of the initial (N-terminal) portion of the S2 fragment of the myosin tail. A small volume of unfilled density in the light chain domains could accommodate the putative 50% larger volume of the tarantula regulatory light chain (Ref. 26)compared with the vertebrate RLC used in the fitting. Note: while the new model differs from the “splayed heads” structures proposed previously (see Fig. 3 legend of paper), the current and earlier models agree in having interactions between myosin heads that are on the same helical track but in adjacent crowns (see Fig. 5 of paper).
Supplementary Movie5
This movie shows different views of the space filling atomic model of PDB 1i84 after minor modification to fit the J-motif of the reconstruction (cf. Figs 3b and 5a of paper). The bare zone direction is towards the top. The model rotates around a vertical axis through 360 degrees to show views from all sides.
Supplementary Movie6
This movie shows how S2 fits into the reconstruction (cf. Fig. 4 of paper). The initial view shows the J-motif (bare zone at top) fitted with the two heads (Fig. 3a of paper),together with the N-terminal portion of the associated S2 (red; cf. Fig. 5b of paper). The view moves through 90 degrees to expose the S2 and its sloping path towards the subfilaments, and then rotates to produce a horizontal orientation, with bare zone towards the right (cf. Fig. 4a of paper). The view now rotates around a vertical axis, reaching an orientationsimilar to that in Fig. 4bof the paper after 90 degrees, then continuing to complete a 360 degree rotation, showing the two heads and the S2 from all sides in this horizontal plane.