Fig. 2: The putative narrow pore and lipid binding site of the monomeric hTMEM63A channel.

a, b Top view (a) and side view (b) of the transmembrane domain of hTMEM63A channel. The transmembrane helices are marked by 0-9 and colored in the rainbow. The putative narrow pore of hTMEM63A is formed by the M3, M4, M5, M6, and M7. A lipid that plugs the cytosolic entrance of the pore (modeled as POPC) at the intersection of M4 and M6 is shown with its corresponding map density (σ = 3.0) in (a). c Side view of the hTMEM63A transmembrane domain. The calculated pore profile of the putative hTMEM63A is indicated as orange and yellow dots calculated using HOLE. The transmembrane helices in the pore domain are shown in gray. d Pore radius of the hTMEM63A along the z-axis. The positions of the hydrophobic residues F516, F517, and Y520 on M7 that are blocking the pore are marked by arrows and the relative contributions to the pore of other pore-lining helices are shown with the same color coding as in panel (e). e Enlarged cutaway view of the narrow pore of hTMEM63A corresponding to the red box in (c). The transmembrane helices are in gray and the hydrophobic residues are labeled. f Enlarged cutaway view of lipid binding interface corresponding to the purple box in (c). The lipid is shown in blue and plugs the cytosolic entrance of the pore at the intersection of M4 and M6. Residues W473 on M4, E571 on M6, and W613 on M7 coordinately interact with the phosphate head of the putative lipid, while hydrophobic residues on M0 and M4 interact with the acyl chain (relative distances are shown in Å).