Figure 1. Overall structure of T4L‐MICU2 and structural comparison of MICU1 and MICU2.

• A, B
  Space filling and cartoon representation of two MICU2 (A) and T4L molecules (B). The protein chain with two calcium ions bound is colored in yellow, and the protein chain with one calcium ion bound is colored in purple. Calcium ions are shown as red spheres.
• C
  The structure of Ca²⁺‐bound MICU2 (molecule 2) is superimposed with Ca²⁺‐bound MICU1 (PDB code: 4NSD). MICU1 is colored in gray; MICU2 is colored in orange, marine, and green‐cyan for different domains. Calcium ions are shown as blue and red spheres in MICU1 and MICU2, respectively.
• D, E
  Comparison of C‐lobes of MICU2 (green‐cyan) and MICU1 (gray) in the Ca²⁺‐free (D) and Ca²⁺‐bound (E) states.
• F
  Comparison of N‐lobes of MICU1 (gray) and MICU2 (orange) shows large divergence in the EF‐hand 1 (box in red dotted line) and β‐sheet (box in black dotted line). Calcium ions are shown as blue and red spheres in MICU1 and MICU2, respectively.
• G
  Superimposition of MICU2 EF‐hand 2 in Ca²⁺‐bound (green‐cyan) form and Ca²⁺‐free form (bright green). Calcium ion is shown as a red sphere.
• H
  Superimposition of MICU2 EF‐hand 1(with Ca²⁺‐bound) and MICU1 Ca²⁺‐bound EF‐hand 1. Calcium ions are shown as blue and red spheres in MICU1 and MICU2, respectively.
• I
  Superimposition of MICU2 EF‐hand 1 (with Ca²⁺‐bound) and MICU1 Ca²⁺‐free EF‐hand 1. The angle (yellow) represents the conformational difference. The calcium ion in MICU2 is shown as a red sphere.