Fig. 6. Rearrangement of the extracellular vestibule.

a Superposition of the pore region of the rebuilt Ca²⁺-free apo (PDB: 5OYG) and the 1PBC/Ca²⁺-bound structures viewed from within the membrane. b α3 and α4 of the superposed structures in Cα representation. The Cα atoms of Gly 510 are shown as spheres. c α3 and α4 with respect to the other pore-forming helices in the superposed structures viewed from the extracellular side. Selected residues on α3 are displayed. d Close-up view of the residues that rearrange upon the binding of 1PBC. e Molecular surface of the extracellular vestibule viewed from the top of the membrane. Selected residues lining the volume are shown. a–e The 1PBC/Ca²⁺ structure is shown in green and the Ca²⁺-free apo structure in gold.