FIGURE 3. Structural analysis of the I state of mutants G48M and G48V of Fyn SH3 using chemical shifts.

a, Ratio of ¹⁵N chemical-shift differences, |^exp(k)| = |_FI(k)/_FU(k)|, plotted on the ribbon trace of the structure of the wild-type Fyn SH3 domain²⁷, with the colour code indicated. Residues with values of ^exp < -0.5 or ^exp > 2.5 are in grey. b, Comparison of ^exp (filled squares) with the ^calc values obtained in the structure determinations (lines); only residues with more than four native contacts have been represented. c, Ribbon representation of the ensemble of 25 structures determined for each mutant; the structure with the thicker ribbon is the more representative (lowest average pairwise r.m.s.d.) of the ensemble. d, Average effective energy contact map of the native state (bottom) and the ensembles obtained for the I state of each mutant (top); E_ij is the interaction energy (in kcal mol^-1) between the side chains of residues i and j according to the CHARMM19 force field. Residue numbers are indicated along each of the axes.