Interaction of ibogaine with human alpha3beta4-nicotinic acetylcholine receptors in different conformational states.

Ibogaine blocks human alpha3beta4-nicotinic acetylcholine receptors (AChRs) by binding to a site in the receptor's ion channel, with about nine times higher potency than phencyclidine (PCP). Ibogaine binds with relatively high affinity (Kd = 0.46 ± 0.06 μM) to a single site in the channel and dissociates more slowly from the desensitized receptor than from the resting one, which may prolong the desensitized state. PCP inhibits ibogaine binding, indicating overlapping binding sites between the serine and valine/phenylalanine rings. The interaction is mainly via van der Waals contacts, with local conformational changes suggested by entropic contributions. These findings suggest ibogaine's mechanism involves stabilizing the receptor in a shut-down state.

Study at a glance

Abstract

The interaction of ibogaine and phencyclidine (PCP) with human (h) alpha3beta4-nicotinic acetylcholine receptors (AChRs) in different conformational states was determined by functional and structural approaches including, radioligand binding assays, Ca2+ influx detections, and thermodynamic and kinetics measurements. The results established that (a) ibogaine inhibits (+/-)-epibatidine-induced Ca2+ influx in h(alpha)3beta4 AChRs with approximately 9-fold higher potency than that for PCP, (b) [3H]ibogaine binds to a single site in the h(alpha)3beta4 AChR ion channel with relatively high affinity (Kd = 0.46 +/- 0.06 microM), and ibogaine inhibits [3H]ibogaine binding to the desensitized h(alpha)3beta4 AChR with slightly higher affinity compared to the resting AChR. This is explained by a slower dissociation rate from the desensitized ion channel compared to the resting ion channel, and (c) PCP inhibits [3H]ibogaine binding to the h(alpha)3beta4 AChR, suggesting overlapping sites. The experimental results correlate with the docking simulations suggesting that ibogaine and PCP interact with a binding domain located between the serine (position 6') and valine/phenylalanine (position 13') rings. This interaction is mediated mainly by van der Waals contacts, which is in agreement with the observed enthalpic contribution determined by non-linear chromatography. However, the calculated entropic contribution also indicates local conformational changes. Collectively our data suggest that ibogaine and PCP bind to overlapping sites located between the serine and valine/phenylalanine rings, to finally block the AChR ion channel, and in the case of ibogaine, to probably maintain the AChR in the desensitized state for longer time.