Figure 1.

Simulation system setup. (A, Side view) The expanded volume at the cytoplasmic side provides sufficient space for extracted polypeptides. BR molecules are shown in green, lipid molecules in yellow, and water molecules in red. (Black lines) Simulation box. (B, Top view) Four unit cells, each containing a BR trimer, form a hexagonal two-dimensional crystal. Colors as before. (C) Mechanical unfolding setup. Either the C- or the N-termini (red and blue sphere, respectively) were subjected to a pulling potential as described in Methods (arrow), enforcing extraction toward the cytoplasmic and extracellular side, respectively. Colors represent the secondary structure of the crystal structure (33). Helices A–G are indicated.