Figure 2. Details of the TC-CD320 binding interface.

(a) Interactions of LDLR-A1 and (b) LDLR-A2 with TC. TC helix α5 is coloured green. Ca²⁺ ions are indicated as orange spheres with corresponding anomalous difference density peaks shown (blue mesh contoured at 4σ). TC and CD320 residues involved in intermolecular contacts and Ca²⁺ coordination are shown as sticks and labelled blue and black, respectively. (c) Close-up views showing octahedral Ca²⁺ coordination in LDLR-A1 (yellow, top) and LDLR-A2 (gold, bottom).