FIGURE 6.

Exchange rates for CaM in the CaM:SEF2-1mp complex. Residues with significant exchange rates are marked with their residue number. The secondary structural elements of CaM are outlined in each panel. The error bars have been left out for clarity. All exchange rates are at a nominal field of 600 MHz. For a numerical data list and further details we refer to Table S2. (a) Exchange rates, R_ex, at 600 MHz and at 308 K, as determined from the ratio of R₂ relaxation rates at 400 and 600 MHz (22). The error in the R_ex is ∼±2 s⁻¹, based on 3% average error in the R₂ derived at 400 MHz, 4% average error in the R₂ derived at 600 MHz, and possible variations in the ¹⁵N chemical shift anisotropy between −150 and −200 ppm. (b) Conformational exchange at a nominal field of 600 MHz and at 308 K as determined with the relaxation-compensated CPMG experiment (20). The difference in R₂ (ΔR_ex) determined with 2δ = 3.6 ms and 2δ = 450 μs in the CPMG is plotted as a function of the CaM sequence. ΔR_ex is the average of measurements at 600 MHz (hard ¹⁵N 180-pulse) and 500 MHz (hard and soft ¹⁵N 180-pulse). The ΔR_ex values at 500 MHz were multiplied with 1.44 to convert to 600 MHz field. The error in the ΔR_ex is ±0.7 s⁻¹, based on the standard deviation between the three individual ΔR_ex experiments. (c) The difference in ΔR_ex (ΔΔR_ex) at 600 MHz determined at 308 and 300 K. The error margin is ±1.4 s⁻¹ (indicated by horizontal lines), based on the average error in ΔR_ex of ±0.7 s⁻¹ at both temperatures.