Figure 4. Correlation between the ¹⁵N conformational exchange linebroadening (Δex) in the 80′s loop of FKBP12 (black) and the differential chemical-shift predictions derived from two crystal forms of FKBP52 (grey).

Model-free [41] analysis of the R₁, R₂ and NOE ¹⁵N relaxation measurements was used to estimate conformational exchange linebroadening [22]. The differences in ¹⁵N chemical shift were predicted with SPARTA+ [49] applied to FKBP12 (PDB code 2PPN [31]) and the first FKBP domain of FKBP52 (PDB code 1Q1C [48] and non-equivalent monomers of PDB code 4LAW [45]). An asterisk indicates not statistical significant conformational exchange linebroadening (<~0.4 Hz). The amide resonances for both Ala⁸⁴ and Gly⁸⁹ are severely broadened due to rapid hydrogen exchange [22], precluding a reliable determination of conformational exchange linebroadening, and the predicted chemical shift differences for these two residues are indicated as open bars.