Figure 6.

A network formed by helix 1, helix 3, helix 4, and helix 6. A: Conformations of the four helices in the outward-open conformation. (Up: side view. Down: top view.) B: Conformations of the four helices in the outward-closed conformation (Up: side view. Down: top view.) Rotation of helix 1 and helix 6 (green arrows) is central to the transition from the outward-open conformation to the outward-closed conformation. The hairpin formed by helix 3 and helix 4 moves together with helix 1 and helix 6 (orange arrows). C: Stable salt-bridges contribute to the mechanical coherence between the different helices. (Left: between helix 4 and helix 6. Middle: between helix 3 and helix 6. Right: between helix 1 and helix 6.) For clarity, helix 1 and helix 6 are highlighted in blue, while helix 3 and helix 4 are in red.