Properties of IQ motifs binding to apo-CaM. (A) RMSF values of apo-CaM and (B) interface areas between IQ motifs and CaM in the apo-CaM–IQ complexes. (C and D) Comparison of the sequences and structures of modeled apo-CaM–IQ complexes, with a cartoon depicting the apo-CaM–IQ interaction modes. Color code: red for CaM, pink for the IQ1 motif, yellow for the IQ2 motif, cyan for the IQ3 motif, and purple for the IQ4 motif. The rectangular box in panel C highlights two residues of IQ1–IQ4 in the hydrophobic pockets of apo-CaMs. The double-ended arrows in the middle panels of panel D indicate the motion of the N-lobe of apo-CaMs. Important residue contacts in the apo-CaM–IQ3 and apo-CaM–IQ4 complexes are highlighted.