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3-D tomogram of insect flight muscle slam frozen during an active contraction.
Composite image illustrating a surface view of an unaveraged 3-D tomogram (orange, top two-thirds) and an axial average along each filament (gold, bottom third) that displays the most frequent and ordered crossbridge forms within each 39 nm repeat as 'motifs'. The boxed crossbridge motif is displayed as a wire-net view superimposed with three atomic models of S1. Red is rigor S1 rebuilt to fit the in situ myosin head, cyan is the unmodified Holmes prepower stroke S1 model and yellow is the unmodified Rayment rigor S1. The particular motif illustrated displays three myosin crossbridges that appear to be at the beginning, middle and end of the power stroke. The 'comet-like' figure boxed near the top is the superimposition of all 26 S1 (red motor domain, cyan regulatory domain) rebuilt to fit active crossbridges, all fanned from a single site on actin (green and blue), compared to rigor S1 in yellow. The cloud of density suggests an axial range of motion of the myosin head as it goes through a power stroke, ending near the rigor position (yellow).
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