Fig. 1
Free energy landscape underlying GlpG’s folding and insertion into a bilayer under low-applied force (Top) Two-dimensional free energy landscape at low-applied force as a function of Z, the average of the z-coordinates of the Cα atoms, and D, the distance between the N-terminus and C-terminus of GlpG. Relative free energies are indicated with colors in units of kT, where blue indicates a low free energy and red indicates a high-free energy. A folding path is shown as a purple line drawn from a highly extended state (Z ≈ −10 Å, D ≈ 250 Å) to the folded state (Z ≈ −3 Å, D ≈ 37 Å). Two metastable (I1 and I2) states are present at intermediate values of D and values of Z that are more negative than the average Z of the folded state. (Bottom) One-dimensional free energy profile along the path shown in the top panel as a function of D. A red double-headed arrow that is 50 Å in length is shown between N and I1. This distance corresponds to the end-to-end distance change during the rate-limiting step of refolding at low force. The first metastable state, I1, is about 6.5 kT less stable than the folded state. I2 is about 9 kT less stable than the folded state. Three locations (α, β, and γ) on the path near the transition state (TS) are also indicated. Representative structures from I1, α, β, and γ are shown in Fig. 2. Representative structures for I2 are shown in Fig. 4
