Figure 2.

(A) Temperature dependence of the fraction of native state f_N measured by the fraction of native contacts 〈Q(T/T_F)〉 for the Gō model (dashed curve) and the native hairpin population (solid curve, temperature scale is given at the top) calculated by using the experimental thermodynamic parameters ΔH = −11.6 kcal/mol and ΔS = −39 cal/(mol⋅K) (ref. 3). By fitting 〈Q(T/T_F)〉 to a two-state model we obtained ΔH = −7.0 kcal/mol and ΔS = −22 cal/(mol⋅K). The thermal average of the radius of gyration 〈R_g〉 (in Å, the right-hand vertical axis) vs. T/T_F is plotted (dotted curve). The location of collapse temperature is marked by an arrow. In the temperature range corresponding to that scanned in the experiments (3) the change in 〈R_g〉 is less than 10%. (Inset) Derivatives of 〈Q〉 (dashed curve) and experimental hairpin population (solid curve) with respect to temperature. The temperature scales are the same as in the main figure. It is seen that folding transition in both the experiment and the simulations is very broad. (B) Probabilities of HB formation P_HBⁱ (i gives the HB number) as a function of T/T_F for the Gō model. P_HBⁱ for the HBs proximal to the hydrophobic cluster (HB_3–14³, HB_4–13⁴, HB_12–5¹¹, HB_13–4¹²) are shown by solid curves, other HBs are represented by dotted curves. Terminal HBs and those near the turn are labeled.