Figure 4.

Shown for FN-III₇, structural changes occurring at the end of the first plateau. Breakage of hydrogen bonds highlighted in Fig. 1C is immediately followed by straightening of the β-bulge. Atoms of the β-bulge of the A-strand are shown as green spheres. Atoms in red represent the interlocking Ile⁸⁷ residue from the G-strand also specified in Fig. 1C. Straightening of the β-bulge creates a gap sufficient for 1–3 waters, shown in yellow, to solvate part of the hydrophobic core that includes Tyr³⁴ and Trp²³. After these events at extensions (a) 7 Å and (b) 9 Å, the module extends to the aligned state.