Figure 4.

The kinetic mechanism describing the folding of the FBP WW domain. E represents unfolded states in which loop 2 is extended, U represents the state in which loop 2 is collapsed but not native-like, and the remainder of the protein is unformed. U′ represents the state in which loop 2 is fully native-like, and the remainder of the protein is unformed. M represents the state in which loop 2 is misregistered, and the remainder of the protein is fully native-like. N represents the native state, in which the complete protein is formed. The observed rate constants (k_obs = k_for + k_rev) are k₁ = 3.9 × 10⁻⁵ τ⁻¹, k₂ = 5.8 × 10⁻⁶ τ⁻¹, and k₃ = 1.7 × 10⁻⁴ τ⁻¹, where τ is the fundamental time scale.