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	Fig. 1. Structure and function of chlorpromazine (CPZ) and analogs. (A–C) Chemical structures of CPZ, bromopromazine (BrPZ), and methanethiosulfonate-promazine (MTS-PZ), respectively. (D) Electrophysiological recordings from Xenopus oocytes expressing ELIC. Channels were activated by the application of the agonist GABA at the EC50 (20 mM). In the presence of 30 μM CPZ, this response was reduced. (E) Concentration–inhibition curve for CPZ on ELIC. Averaged data ± SEM are shown for three to nine different oocytes.
	Fig. 2. X-ray crystal structures of ELIC in complex with chlorpromazine (CPZ) and bromopromazine (BrPZ). Side view (A) and top view (B) of ELIC in complex with CPZ in blue ribbon representation. The green mesh represents fivefold averaged Fo-Fc difference electron density contoured at a level of 6σ. The Inset (C) shows a detailed view of the β8–β9 loop binding site and its location relative to the Cys-loop, the M2–M3 loop, and the pre-M1 region. CPZ is shown in stick representation. Yellow is carbon, blue is nitrogen, green is chlorine, and orange is sulfur. Side view (D) and top view (E) of ELIC in complex with BrPZ in blue ribbon representation. The red mesh represents fivefold averaged anomalous difference electron density contoured at a level of 10σ. The Insets show a detailed view of the β8–β9 loop binding site (F) and the agonist binding site (G).
	Fig. 3. Conformational change of the β8–β9 loop in ELIC. (A) Stereo representation of the β8–β9 loop in ELIC. The ELIC backbone is shown as green ribbon. Chlorpromazine (CPZ) is shown in yellow sticks. The blue mesh is simple electron density (2Fo-Fc) contoured at a level of 1.4σ. (B) Superposition of a single monomer of apo ELIC in yellow (PDB ID code 2VL0) and ELIC in complex with CPZ in cartoon representation. The Inset shows a detailed view of the β8–β9 loop. CPZ is shown in sphere representation. White is carbon, blue is nitrogen, green is chlorine, and orange is sulfur. (C) Detailed view of amino acids involved in ligand interactions with CPZ. Dashed lines indicate hydrogen bonds. CPZ is shown in stick representation.
	Fig. 4. Cysteine-scanning mutagenesis of the β8–β9 loop in ELIC. (A) Electrophysiological recordings of Cys-less ELIC in response to repetitive pulses of GABA at the EC50 (=20 mM) and application of 200 µM of a thiol-reactive CPZ derivative termed MTS-PZ. (B) Example traces of a Cys mutant, E155C, showing no effect of MTS-PZ. (C) Example traces of a Cys mutant, D158C, showing an inhibitory effect of MTS-PZ. (D) Summary of MTS-PZ–mediated channel inhibition on the different Cys mutants. Data represent the mean ± SEM of three to five experiments. *P < 0.05, significantly different from Cys-less ELIC, Student’s t test; **P < 0.01, significantly different from Cys-less ELIC, Student’s t test.
	Fig. 5. Binding stability of CPZ in simulations. (A and B) Binding of CPZ measured by the distance from F126 and W160 to the C11 atom of CPZ (solid and dashed lines, respectively) per subunit. (C) Allosteric cavity volume in presence and absence of CPZ; the crystal structure value is indicated by the dashed line. (D) Average hydrogen bond interactions of CPZ. (E) Probability distribution of side-chain angles relative to CPZ; measured from Cβ–Cα–NC2 atom positions. (F) MTS-PZ–mediated inhibition (purple, no significant effect; green, inhibition). Outliers (T149, E155) are marked with black arrows.
	Fig. 6. Overview of allosteric binding sites in different conformational states of Cys-loop receptors. Overview of allosteric binding sites in the closed, open, and desensitized states of Cys-loop receptors. (A) Green ribbon representation of α7-AChBP structure as an example of “ligand binding domain-only” structures (54). (B) Green ribbon presentation of the ELIC ion channel as a representative example of a closed state (27). (C) Green ribbon presentation of the GluCl+ivermectin ion channel structure as a representative example of an open state (30). (D) Green ribbon presentation of the β3 GABAA receptor structure as a representative example of a desensitized state (32). Allosteric modulators identified in the different conformational states are shown in sphere representation. Identical color codes have been used for overlapping sites in the different states, for example, orthosteric site in yellow, vestibule site in firebrick, etc. Detailed explanation of PDB ID codes, allosteric modulator color codes, and references for all structures used in this figure are given in Table S3.

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