Figure 4.

Folding kinetics of PDZ2 measured by intrinsic and extrinsic fluorescence. The data are reported in comparison with X11 PDZ1-PDZ2 and PDZ1. The chevron plot obtained for PDZ2 F761W is reported in green, whereas the data obtained by extrinsic fluorescence and measured in the presence of ANS on wildtype PDZ2 are reported in blue. Of interest, PDZ2 F761W displays an additional roll-over effect indicative of the presence of an additional folding intermediate. Importantly, however, in the case of PDZ2 F761W, analysis with a three-state folding model returns and m_D–N of 1.2 ± 0.2 kcal mol⁻¹ M⁻¹, which is consistent with the (un)folding of a single PDZ unit. ANS, 8-anilino-1-naphthalenesulfonic acid.