Figure 3.

Kinetic scheme for the interaction of SH3^MutΔ56 with apo GroEL. The populations of states U_E and U_B, colored gray, are below the limits of detection and were therefore not included in the fitting of the relaxation data (see the Supporting Information for theory and details of the fitting procedure). The rate constants and populations relate to experimental conditions of 100 μM SH3 domain and 120 μM (in subunits) GroEL at 10 °C. Binding of the dimer F_D to GroEL is assumed to be undetectable because of both its size and the fact that dimerization occludes the GroEL-binding surface (Figure S6). For SH3^WTΔ57, there is no evidence of the existence of an unfolded state as no relaxation dispersion is observed. The ¹⁵N ΔR₂ and DEST data for SH3^WTΔ57 (Figure S7) show binding of the folded state to GroEL and are explained by two-state exchange between states F and F_B, with k_FB and k_BF values of ~7 and 500 s⁻¹, respectively (corresponding to p_B ~ 1.4%).