Bupropion inhibits human α3β4 nicotinic acetylcholine receptors by interacting with luminal and non-luminal sites

Abstract

The interaction of (±)-bupropion [(±)-BP] with the human (h) α3β4 nicotinic acetylcholine receptor (AChR) is determined by functional and structural approaches. The Ca 2+ influx results indicate that (±)-BP inhibits hα3β4 AChRs with ~2-fold lower potency than that for (±)-2-( N - tert -butylamino)-3’-iodo-4’-azidopropiophenone [(±)-SADU-3-72], indicating that this photoreactive analog can be used to further characterize the (±)-BP binding sites. The competition binding results show that (±)-BP binds to the [ 3 H]imipramine sites at desensitized hα3β4 AChRs with ~4-fold higher affinity compared to the resting state. Molecular docking results indicate that both enantiomers of BP and SADU-3-72, in the protonated state, interact with luminal and non-luminal sites. BP interacts with a luminal site which overlaps that for imipramine, and with non-luminal sites located in the transmembrane domain (TMD) at interfacial (+α3/-β4) and α3 intrasubunit sites, and in the TMD-ECD (extracellular domain) junction at the +β4/-α3 and +β4/-β4 interfaces. Our results are consistent with a hα3β4 model where BP and SADU-3-72 bind to overlapping non-luminal sites as well as non-overlapping luminal sites, probably in physiological conditions.