Figure 4.
The three-dimensional structure of the actin-tropomyosin-myosin S1 complex reconstructed from electron micrographs of negatively stained complexes by assuming the helical symmetry of specimens.39) A. The oblique view from the M-line side. B. The top view of the superposed two-dimensional sections showing the multi-domain structure.41) C. The visual validation of the objective assignment of actin. The top two panels show the actin-tropomyosin-myosin S1 complex on the left, and the actin-tropomyosin complex without myosin S1 on the right. The weighted averages of two structures with various weighting factors were calculated and are shown in the bottom three panels. It was concluded that both of domains A and B correspond to actin-tropomyosin and that the domains A2 and B2 represent the myosin-binding site of actin.