FIGURE 6.

Cpep-binding interfaces of Ca²⁺/CaM. A, weighted chemical shift changes Δδ_ppm (H^N, H) for assigned residues of ¹⁵N-labeled Ca²⁺/CaM following the addition of Cpep at a molar ratio of 4:1 (Cpep/[¹⁵N]CaM). The horizontal line indicates 1 S.D. above the mean chemical shift change. Red bars correspond to residues deemed to have undergone significant chemical shift changes (>1 S.D.). Cyan bars correspond to residues that underwent even larger chemical shift changes but could not be traced during the titration or did not reappear in the spectrum. B, annotated structure of Ca²⁺/CaM (PDB 1CCL) showing the locations of the perturbed residues as identified in A. Residues corresponding to cyan bars and red bars in A are shown as cyan and red spheres, respectively. Bound calcium atoms are shown as black spheres. For clarity, the left panel highlights only the cyan spheres, and the right panel highlights both cyan and red spheres. C, examples of the fitted binding curves for residues in fast exchange, including Ala⁵⁷, Val¹²¹, and Ile¹³⁰ (see Table 2 for corresponding K_D values).