Figure 2.

Overview of calmodulin structure and Ca²⁺ binding conformations. (A) Calmodulin (CaM) structure comprises four EF-hand structures, two each on N- and C-termini that are connected via an inter-domain helix [6]. CaM exists either as Apo-CaM (no Ca²⁺ bound to EF-hands) or Holo-CaM (Ca₄-CaM or Ca²⁺ ions bound to all EF-hands); (B) Different intermediate calmodulin conformations (Ca₂-CaM) between Apo-CaM and Holo-CaM with Ca²⁺ ions binding to two EF-hands during each step [8].