Figure 5.

Thick filament strands. A. Surface rendering of three dimensional reconstruction from electron micrographs of tarantula leg muscle. Note helically ascending “hills” (strands) and “valleys”. Blue overlay shows the two myosin heads that form the repeating ‘J’ (dashed line in overlay) motif that forms the strands and a portion of the molecule’s rod in the thick filament body. B. Ribbon representation of two myosin heads (the ‘J’ in panel A) showing that one is free and the other is blocked by binding of its motor domain to the motor domain and essential light chain of the free head. Blue, pink, beige are motor domain, essential light chain, and regulatory light chain of the free head. Green, orange, and yellow are same domains for the blocked head. C. The free head of a crown below binds to the essential light chain of the bound head of the crown above (yellow ellipse). The motor domain of the bound head may also interact with the rod portion of the heads from the crown below (yellow curly bracket). Same color code as in B. Modified, with permission, from Woodhead et al. (2005)