Molecular dynamics simulations of dihydro-β-erythroidine bound to the human α4β2 nicotinic acetylcholine receptor

Background and Purpose The heteromeric alpha 4 beta 2 nicotinic acetylcholine receptor (nAChR) is abundant in the human brain and is associated with a range of CNS disorders. This nAChR subtype has been recently crystallised in a conformation that was proposed to represent a desensitised state. Here, we investigated the conformational transition mechanism of this nAChR from a desensitised to a closed/resting state. Experimental Approach The competitive antagonist dihydro-beta-erythroidine (DH beta E) was modelled by replacement of the agonist nicotine in the alpha 4 beta 2 nAChR experimental structure. DH beta E is used both in vitro and in vivo for its ability to block alpha 4 beta 2 nAChRs. This system was studied by three molecular dynamics simulations with a combined simulation time of 2.6 mu s. Electrophysiological studies of mutated receptors were performed to validate the simulation results. Key Results The relative positions of the extracellular and transmembrane domains in the models are distinct from those of the desensitised state structure and are compatible with experimental structures of Cys-loop receptors captured in a closed/resting state. Conclusions and Implications Our model suggests that the side chains of alpha 4 L257 (9 ') and alpha 4 L264 (16 ') are the main constrictions in the transmembrane pore. The involvement of position 9 ' in channel gating is well established, but position 16 ' was only previously identified as a gate for the bacterial channels, ELIC and GLIC. L257 but not L264 was found to influence the slow component of desensitisation. The structure of the antagonist-bound state proposed here should be valuable for the development of therapeutic or insecticide compounds.