(A) Docking crystal structure into helical reconstructed cryo-EM map (transparent gray). G domain is colored in green, BSE domain in cyan, middle/GED stalk in blue, and paddle domain in yellow. The magenta colored models represent molecules in one helical rung of S-OPA1 assembly. And the building blocks of one helical rung, the dimers of S-OPA1, are shown in the surface representation with the color dark-red, red, gold, yellow and light-yellow, respectively. (B) Zoomed–in view of radical cross-section showing the fitness between structural model and the map. (C) Vertical cross section of the map that rotates 90° with respect to (B). Dashed black lines denote the positions of the cross sections in (D). (D) Cross sections of the tube showing the fitness between structural model and the map. Putative G dimer interface (G) is shown in panel 1. The stalk interaction interfaces-1,2 and 3 (I1, I2 and I3) are indicated in panel 2. And the paddle interaction interface P1 as well as interface-2 (I2) are indicated in panel 3. (E) Structural model of the left-handed S-OPA1 assembly on membrane at nucleotide-free state. The four interfaces (I1, I2, I3 and P1) for the stability of S-OPA1 assembly are indicated with red circles. The orientation of the helical rung is indicated with black lines.