Role of the Cys Loop and Transmembrane Domain in the Allosteric Modulation of ?4?2 Nicotinic Acetylcholine Receptors.

ABSTRACT: Allosteric modulators of pentameric ligand-gated ion channels are thought to act on elements of the pathways that couple agonist binding to channel gating. Using ?4?2 nicotinic acetylcholine receptors and the ?4?2-selective positive modulators 17?-estradiol (?EST) and desformylflustrabromine (dFBr), we have identified pathways that link the binding sites for these modulators to the Cys loop, a region that is critical for channel gating in all pentameric ligand-gated ion channels. Previous studies have shown that the binding site for potentiating ?EST is in the C-terminal (post-M4) region of the ?4 subunit. Here, using homology modeling in combination with mutagenesis and electrophysiology, we identified the binding site for potentiating dFBr on the top half of a cavity between the third (M3) and fourth transmembrane (M4) ?-helices of the ?4 subunit. We found that the binding sites for ?EST and dFBr communicate with the Cys loop, through interactions between the last residue of post-M4 and Phe170 of the conserved FPF sequence of the Cys loop, and that these interactions affect potentiating efficacy. In addition, interactions between a residue in M3 (Tyr309) and Phe167, a residue adjacent to the Cys loop FPF motif, also affect dFBr potentiating efficacy. Thus, the Cys loop acts as a key control element in the allosteric transduction pathway for potentiating ?EST and dFBr. Overall, we propose that positive allosteric modulators that bind the M3-M4 cavity or post-M4 region increase the efficacy of channel gating through interactions with the Cys loop.

SUBMITTER: Alcaino C 

PROVIDER: S-EPMC5241731 | biostudies-literature | 2017 Jan

REPOSITORIES: biostudies-literature