Probing the Binding Site(S) of Bupropion in Glic by Site-Directed Mutagenesis

Abstract

Bupropion, an atypical antidepressant, has been shown to ameliorate the neurotransmission of both dopamine (DA) and norepinephrine (NE) by inhibiting their respective transporters in the brain. However, the clinical efficacy of bupropion is likely not due solely to its inhibition of DA and NE reuptake. The poor understanding of bupropion's mechanism of action (MOA) stems from the diversity of its molecular targets. Indeed, bupropion additionally inhibits key members of the Cys-loop superfamily, broadly known as pentameric ligand-gated ion channels (pLGIC). Allosteric inhibition by bupropion of some of the nicotinic acetylcholine receptors (nAChRs) has been implicated in its clinical efficacy as a smoking cessation aid. We recently reported for the first time that, in addition to bupropion's currently known actions, it is also an allosteric antagonist of the serotonin type 3A receptor (5-HT3AR). Our new finding adds another dimension to the complex conundrum of bupropion's MOA, and suggests an additional pharmacological principle underlying its efficacy as an antidepressant. In the continuum of exploring bupropion's actions on several members of pLGICs, we now are investigating bupropion's functional and binding interactions with the Gloeobacter violaceus ligand-gated ion channel (GLIC), a prokaryotic homologue of pentameric ligand-gated ion channels. To achieve the stated goals of our investigation, we have been utilizing an array of techniques including molecular docking, site-directed mutagenesis, cysteine modification, and two-electrode voltage clamp recording (TEVC). Further studies are in progress to identify specific interaction site(s) in GLIC, which can be conserved across the eukaryotic members of pLGICs.