Pore-lining residues suggest octameric arrangement of CLDN15 monomers. (A) Octameric channel structure reveals contribution of lateral monomers (L1, L2, L3, L4) to central monomers (A1, A2, A3, A4). (B) Pore-lining residues include H35, G36, N37, V38, I39, T40 from β1β2 regions on lateral subunits, as well as residues P149, L150, Y151 from ECS2 regions on primary subunits. (C) Sequence of negatively charged E46, D64, D55, and polar residue N61 located on the channel’s primary subunits.