Fig. 5: The His-rich loop incorporates into the cytosolic cavity of the IF protomer.

a Superimposition of the TMDs of the hZnT7 heterodimers in IF-OF form (gray) and Zn²⁺ state 1 (colored as indicated), viewed from the Golgi lumen (left) and cytosol (right). Black arrows indicate the movement of TM5 during the conversion from the IF-OF form to Zn²⁺ state 1. b Bending of the N-terminal portion of TM5 in the IF protomer of Zn²⁺ state 1. The density map of TM5 is shown by blue mesh at a contour level of 0.17σ. c Superimposition of TM5 in the IF protomers of the hZnT7 heterodimers in IF-OF form (gray) and Zn²⁺ state 1 (yellow). Black and red arrows indicate the movements of TM5 and His240 in TM5 during the transition from the Zn²⁺-unbound state to Zn²⁺ state 1, respectively. d Superimposition of TM4 and TM5 between the IF protomers in the Zn²⁺ state 1 (yellow) and Zn²⁺ state 2 (blue). The yellow and blue spheres indicate an Zn²⁺ ion bound to the Zn²⁺ state 1 and Zn²⁺ state 2, respectively. The red arrow indicates the movement of His240 during the transition from the Zn²⁺ state 1 to state 2. The black dash-line square is highlighted in the right upper inset with the density map around His240 in the Zn²⁺ state 2. e Highlighted representation of the His-loop segment viewed from the cytosol (upper) and side (lower). The His-loop segment is shown in magenta with its density map (blue) at a contour level of 0.17σ. TM4 and TM5 were shown in yellow. A red sphere indicates a Zn²⁺ ion coordinated by His164.