Figure 2.

Three-dimensional structures and dynamics of SO-BP. A, overall structure of the ligand-free open form, consisting of domain I (35–145 and 301–349, green), domain II (148–298 and 352–416, purple), and hinge regions (146–147, 299–300 and 350–351, orange). B, overall structure of the closed form in complex with Sop₄. Each domain is colored as in A. Sop₄ is shown as a stick model and colored with cyan. C, conformational change of SO-BP. The complex structure with Sop₄ is overlaid with the open form structure (gray) in domain II. D, plot of the distances between the Cα atoms of the open and closed forms calculated from C. A red line indicates distance criteria at 2.0 Å for the fixed and mobile regions, which define domain divisions shown above the graph. E, two representative structures of the open form SO-BP obtained by MD simulation. These colors correspond to the structures shown in F. These structures are overlaid in domain II. F, two-dimensional projection of the conformational ensembles on the first and second principal axes. The initial structure (black circle) and the two representative structures with the highest occurrence ratios (blue and orange triangles) are plotted in the projection.