The Trp-cage and E6apn1. (a) Helix content h against temperature. The lines are two-state fits (Tm = 309.6 ± 0.7 K and ΔE = 11.3 ± 0.3 kcal/mol for the Trp-cage; Tm = 304.0 ± 0.5 K and ΔE = 14.2 ± 0.3 kcal/mol for E6apn1). (b) Free energy F calculated as a function of bRMSD at two different temperatures, 279 K (solid lines) and 306 K (dashed lines). The double lines indicate the statistical errors.