Fig. 1

Figure 1. Side-chain orientations of E121 in zfP2X4 and equivalent residues in other P2X receptors. A, residues E121, R298, and K313 highlighted in the open structure of zfP2X4 (Protein data Bank [PBD] ID: 4DW1). The different domains are named head, dorsal fin (DF), left flipper (LF), right flipper (RF), body and fluke, respectively. B, zoom-in view of the location of E121 (upper) and 2Fo–Fc omit map for E121 (lower) in zfP2X4 at the resting (PDB ID: 4DW0, left) and open (right) states. Red circles indicate the atoms chosen to define the dihedral angle χ_{Cα–Cβ–Cγ–Cδ}. C, the sequence alignment of the head domain in P2X family. Pink boxed regions highlight the highly conserved residue E121/E118 and nonconserved residue R143/H140 (zfP2X4/rP2X4 numbering) in P2X receptors. Sand bar indicates residues in the beak region. D–G, side-chain orientations of E109 in the apo (PDB ID: 5SVJ) and open (PDB ID: 5SVK) crystal structures of hP2X3, E129 in the open structure of AmP2X (PDB ID: 5F1C) (E), E109 in the crystal structure of ckP2X7 in complex with inhibitor (PDB ID: 5XW6) (F) and D121 in the apo crystal structure of pdP2X7 (PDB ID: 5U1L) (G). H, the side-chain orientation of E121 in the cryo-EM structure of rP2X7 at the resting (PDB ID: 6U9V) and open (PDB ID: 6U9W) states. rP2X4, rat (Rattus norvegicus) P2X4; zfP2X4, zebrafish (Danio rerio) P2X4.