Two-dimensional projections of protein A folding network: (a) Calculated φ-values for the wild-type (blue line) and perturbed (black line) contact matrices are shown together with the wild-type melting values (green line). Measured φ-values for surface (open symbols) and core (filled symbols) residues are from (Sato S, Religa TL, Daggett V, Fersht AR 2004 Proc Natl Acad Sci USA 101:6952-6956). (b and c) Free energy landscapes for two contact models. The landscapes are a projection of the folding network onto the coordinates qN = ∑ i ≤ N/2 qi and qC = ∑ i > N/2 qi, where n=60. (b) The wild-type NMR structure. (c) The same structure weighted by the function (1 + 5/rij)/2 for ξ corresponding roughly to 2M GdmCl at 25°C (levels on the landscapes are separated by ~0.1kT).