Figure 4: Ca²⁺-induced conformational changes of CaM determine its distinct interactions with IQCG.

(a) Cartoon representation of the Ca²⁺-free CaM (N-lobe coloured in green, whereas C-lobe in cyan) in complex with IQCG IQ motif (in magenta) compared with its complex with IQ2 from myosin V (in white; lower panel). (b) Ca²⁺-bound CaM (N-lobe in yellow, whereas C-lobe in blue) in complex with IQCG (in orange) compared with its complex with CaMKIIδ (in white; lower panel). Ca²⁺ ions are shown as red spheres. (c) Superposition of the Ca²⁺-bound CaM–IQCG complex on the Ca²⁺-free counterpart based on the IQ motif (residues 400–410) of IQCG. Note that the conformations of each CaM lobe as well as the positions of the lobes undergo large changes as a result of Ca²⁺ binding.