(D) Structural arrangement of COX subunits detected in association with SC I+III2. Upper illustrations depict lateral views of human SC I+III2+IV1, where CI (aquamarine) and CIII2 (light green) are positioned along the inner membrane plane (dots). CIV appears as a smooth backbone with the associated COX subunits highlighted to show their positions relative to SC I+III2: COX7A2 (blue) and COX5B (red) attach COX1 (yellow) to the concave surface formed by CIII2 and the CI membrane arm, interaction further stabilized by COX7C (green) binding to CI. COX4 (magenta) interacts with COX1 on the distal side of CIV. Medium illustrations: matrix (M) view. Lower illustrations: intermembrane space (IMS) view. The figure was created with USCF Chimera v.1.12 using the 5XTH structure (Guo et al., 2017) from the PDB database. 