Fig. 3: The putative pore of hXPR1.

a. (left) The solvent-accessible surface of the hXPR1 TMD colored by ±5 kT/e electrostatic potential calculated using APBS⁵⁸. The secondary structures of TM1–4 are shown in grey and TM5–10 in light cyan. The positively charged vestibule formed at the center of the barrel-shaped helical bundle of TM5–10 is boxed in red. Two solid black lines indicate the membrane boundary. (right) The electrostatic surface–potential map depicting the same vestibule alone, view orthogonally from the extracellular space. b. The putative pore location in hXPR1 inside the 6-helix barrel colored light cyan, and pore pathway is depicted as purple mesh. The residues on the TM5–10 that are conserved among hXPR1, atPHO1, and scSYG1 are colored in dark green. c. Pore radius along the z coordinate. d, e Detailed view of the green-colored conserved pore-lining residues shown in stick model on TM5, 7, and 9 d, and TM6, 8, and 10 e.