FIGURE 5.

Generated stability curves for PGB1-QDD based on experimental pK_a values for the native state and calculated pK_a values for the unfolded state (Table 1), which are compared to pH-dependent denaturation data (7). (a) Curves generated in low salt where the unfolded state is modeled as a Gaussian chain (dashed), model pK_a values (dashed-dotted) Gaussian chain but the pK_a value of D37 is shifted to 6.0 (solid), and a uniform pK_a shift of 0.2 units (dotted). All curves in a are generated using a pK_a value of 8.9 for the N-terminus in the folded state. (b) Curves generated in 0.5 M salt where the pK_a values of the unfolded state were modeled as a Gaussian chain but where the pK_a value of the N-terminus is 9.0 (solid) and 7.5 (dashed). Experimental stability data in low salt (•) and 2 M NaCl (▴). In a, the calculated curves were shifted to minimize the rms deviation between experimental and calculated data points. In b, the curve was shifted to fit experimental data at pH >5.