Fig. 1.

The reaction network of the pB ^′ to pB transition. (A) Structures of metastable states in the pB ^′ to pB transition (see main text for a description). The helix α3 is rendered blue, and the stick models represent relevant residues: pCA (yellow), Glu46 (red), Tyr42 (green) and Thr50 (orange). Black dotted lines indicate hydrogen bonds. Water molecules are shown as pink and white stick models. (B) Free-energy profile projected in the dXE - rmsd _α plane. The labeled ellipses roughly indicate the location of the metastable states. The gray contour lines indicate the free-energy profile obtained from a previous REMD simulation, separated by 1k _B T (19). The blue stars indicate the conformations obtained by time-resolved NMR on a mutant of PYP (13).