The 1H-15N HSQC spectra of uniformly 15N-labeled CaM (1.25 mM, black contours) and uniformly 15N-labeled CaM mixed with unlabeled rmMBP (0.64 mM CaM + 0.80 mM rmMBP, red contours). The resonance assignments shown are for unbound CaM and are from Ikura et al. (114); the labels shown correspond to the black (unbound) contours and indicate the secondary structure element (L = loop or H = α-helix) with which each residue is associated. Crosspeaks that have obvious assignments are shown connected with black lines. Both spectra were recorded on samples in 100 mM KCl, 8 mM CaCl2, pH 6.5, 10% D2O, 0.75 mg DSS at 300 K.