Fig. 2. From relaxation dispersion NMR data to binding mechanisms.

a, b Effective transverse relaxation rate R_2,eff versus nutation frequency ν of the applied transverse field measured by ¹⁵N relaxation dispersion for the amide of the ubiquitin residue 49 in the presence of 0.1 mM and 0.5 mM of SH3c. The blue and yellow data points result from measurements at the two ¹⁵N resonance frequencies 60.795 MHz and 96.313 MHz. The gray lines represent fits in the fast-exchange regime to determine the exchange rate k_ex (“Methods”). c The obtained exchange rates k_ex of the ubiquitin residue 49 (black data points) decrease with increasing SH3c concentration, which indicates conformational selection. The blue and red lines with shaded error regions result from fits of the k_ex equations of the two-state and conformational-selection binding mechanism (Fig. 1, Supplementary Methods). d For the amide of the SH3c residue 280, the exchange rate k_ex increases with the ubiquitin concentration and can be well fitted with the k_ex equation of two-state binding. e Unbinding rates k_off obtained from fits with the conformational-selection model for ubiquitin residues (blue data points) and from fits with the two-state binding model for SH3c residues (red data points, Supplementary Figs. 3 and 4). f Conformational excitation rate k₁₂ from conformational-selection fits of ubiquitin residues (Supplementary Fig. 3). Global and residue-specific uncertainties in the R_2,eff values were estimated as described in Methods. The larger one of these two uncertainty estimates for each data is reported (smaller than the plot markers). The error bars in (c–f) represent standard errors of data fits (“Methods” and Supplementary Methods). Source data are provided as a Source Data file.