Fig. 1.

Cryo-EM Structure of the AtTPC1_DDE–saposin A–Fab complex. (A) Side (Left) and top-down (Right) views of cryo-EM density. The composite map is colored to highlight high-resolution features of TPC1 (blue, EMDB entry no. 8957), VSD2 in state 1 (cyan, EMDB entry no. 8958) and state 2 (pink, EMDB entry no. 8960), and the Fab variable domains (orange, EMDB entry no. 8956). Unsharpened density is shown at low contour (transparent gray). Membrane boundaries (black bars) defined by the nanodisc are marked. (B) Overlay of AtTPC1_WT (red, PDB ID code 5DQQ), state 1 (blue), and state 2 (pink). Ca_i²⁺ and Ca_a²⁺ denote sites of luminal inhibition and cytoplasmic activation by Ca²⁺ ions. Dash lines around Ca_a²⁺ indicate hypothetical position in cryo-EM structure. Ca²⁺ ions shown as colored balls.