Figure 1.

Free CypA undergoes exchange on multiple chemical shift timescales. (A) Nearly half of CypA exhibits chemical exchange contributions (cyan) above 0.5 s⁻¹ (Supporting Information Table S1). (B) The static magnetic field dependence of chemical exchange is used to calculate α at 20°C, 10°C and 0°C from Supporting Information Table S2.²³ R2-CPMG dispersion is shown at 600 MHz (dashed lines, ▪) and 900 MHz (straight lines, •) for R55 and L122. Dispersion curves for L122 at 10°C and 0°C exhibit no static field dependence (i.e. α = 0) and thus, the absolute R2^eff is shown for clarity to avoid overlap of their calculated fits. (C) The temperature dependence of R_ex is shown for these same residues and is in good agreement with the static magnetic field dependence. R_ex increases with lower temperatures for R55 and decreases for L122, indicating fast exchange and slow exchange, respectively.¹ Data were collected at 20°C (orange), 10°C (blue), and 0°C (cyan). [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]