Fig. 3

Structure of Zn²⁺-bound form of ERp44. a Top and side view of the overall structure of the Zn²⁺-bound dimer of ERp44. The a, b, b′ domains and C-tail of Mol A and Mol B are shown in green, yellow, blue and magenta, respectively. The Zn²⁺ ions are represented by orange spheres. A vertical black line represents a non-crystallographic twofold axis. The right insets display the close-up views of the three Zn²⁺ binding sites: site 1 (top), site 2 (middle) and site 3 (bottom). Simulated annealing 2Fo−Fc omit maps at 1–1.3σ and anomalous difference Fourier map at 15σ are shown in brown and magenta, respectively. b Close-up views of the dimer interfaces; (left): highlighted view of the red box in a, which illustrates interactions formed between the α12 helices of the b′ domains in ERp44 dimer; (right): highlighted view of the blue box in a, which illustrates interactions formed between the C-tail of Mol A and the a domain of Mol B. Hydrogen bonds and van der Waals contacts are shown by blue and yellow dashed lines, respectively. c Comparison of the overall structure of the Zn²⁺-bound (left) and unbound (right) forms of the ERp44 protomer. The essential cysteine (Cys29) is shown as spheres