Fig. 1. Cryo-EM maps and modeled structures of human SPCA1a in the E1-Ca²⁺/Mn²⁺-ATP and E2P states.

(A) ATPase activities of purified human SPCA1a in the presence of 10 μM Ca²⁺ (Ca), 10 μM Ca²⁺ + 446 nM megabody 14 (Ca + Mb14), 10 μM Mn²⁺ (Mn), 10 μM Co²⁺ (Co), or 10 μM Ni²⁺ (Ni) and in the absence of them (CTRL). All measurements were made in triplicate. (B) Domain organization of SPCA1a. SPCA1a contains three cytosolic domains, A-domain (orange), P-domain (blue), and N-domain (hot pink), and TM1–2, TM3–4, and TM5–10 helix clusters (green, violet, and wheat, respectively). (C to E) Cryo-EM density maps of SPCA1a in the E1-Ca²⁺-AMPPCP (C), E1-Mn²⁺-AMPPCP (D), and E2-BeF₃⁻ (E) states. (F to H) Ribbon diagrams of cryo-EM structures of SPCA1a in the E1-Ca²⁺-AMPPCP (F), E1-Mn²⁺-AMPPCP (G), and E2-BeF₃⁻ (H) states. The cytoplasmic domains (A-, P-, and N-domains), TM subdomains (TM1–2, TM3–4, and TM5–10), and the head domain of the megabody are colored as in (C) to (E). Ligands (AMPPCP, BeF₃⁻, Ca²⁺, and Mn²⁺) bound to SPCA1a are highlighted in circles.