Fig. 4: Crystal structure of the EF-hand pair of CRACR2a in complex with LIC1_433–458.

a Ribbon diagram and surface representation of the structure of the complex of human CRACR2a_47–122 (the first and second EF-hands are colored dark and light orange, respectively) with LIC1_433–458 (blue). The side chains of LIC1_433–458 are shown using a stick representation and colored by atom type. b, c Close-up views showing the binding of LIC1_433–458 in a hydrophobic cleft formed between the incoming (α1 and α3) and exiting (α2 and α4) helices of the two EF-hands. The 2Fo–Fc electron density map (blue mesh) contoured at 1.0σ is shown around an all-atom representation of the LIC1 helix. Note that residues on the hydrophobic face of the LIC1 helix insert into the hydrophobic cleft formed by the EF-hand pair (side chains colored gray). d Close-up view of the Ca²⁺-binding loop (located within the second EF-hand) of human CRACR2a (left) compared to the third Ca²⁺-binding loop of human troponin C (middle, PDB code: 1J1D) and the first Ca²⁺-binding loop of human calmodulin (right, PDB code: 1CLL). The 2Fo–Fc electron density map (blue mesh) contoured at 2.5σ is shown around the atoms of CRACR2a and a Fo–Fc difference map (green mesh) contoured at 5.0σ is shown around the bound Ca²⁺ ion.