Weak toxin WTX from Naja kaouthia cobra venom interacts with both nicotinic and muscarinic acetylcholine receptors.

Mordvintsev, Dmitry Yu.; Polyak, Yakov L.; Rodionov, Dmitry I.; Jakubik, Jan; Dolezal, Vladimir; Karlsson, Evert; Tsetlin, Victor I.; Utkin, Yuri N.

Iodinated [125I] weak toxin from Naja kaouthia (WTX) cobra venom was injected into mice, and organ-specific binding was monitored. Relatively high levels of [125I]WTX were detected in the adrenal glands. Rat adrenal membranes were therefore used for analysis of [125I]WTX-binding sites. Specific [125I]WTX binding was partially inhibited by both α-cobratoxin, a blocker of the α7 and muscle-type nicotinic acetylcholine receptors (nAChRs), and by atropine, an antagonist of the muscarinic acetylcholine receptor (mAChR). Binding to rat adrenal nAChR had a Kd of 2.0 ± 0.8 μm and was inhibited by α-cobratoxin but not by a short-chain α-neurotoxin antagonist of the muscle-type nAChR, suggesting a specific interaction with the α7-type nAChR. WTX binding was reduced not only by atropine but also by other muscarinic agents (oxotremorine and muscarinic toxins from Dendroaspis angusticeps), indicating an interaction with mAChR. This interaction was further characterized using individual subtypes of human mAChRs expressed in Chinese hamster ovary cells. WTX concentrations up to 30 μm did not inhibit binding of [3H]acetylcholine to any subtype of mAChR by more than 50%. Depending on receptor subtype, WTX either increased or had no effect on the binding of the muscarinic antagonist [3H] N-methylscopolamine, which binds to the orthosteric site, a finding indicative of an allosteric interaction. Furthermore, WTX alone activated G-protein coupling with all mAChR subtypes and reduced the efficacy of acetylcholine in activating G-proteins with the M1, M4, and M5 subtypes. Our data demonstrate an orthosteric WTX interaction with nAChR and an allosteric interaction with mAChRs.

TOXINS; VENOM; CHOLINERGIC receptors; LABORATORY mice; GENE expression

FEBS Journal, 2009, Vol 276, Issue 18, p5065

1742-464X

Academic Journal

10.1111/j.1742-4658.2009.07203.x