title: Pharmacological characterization of α-elapitoxin-Al2a from the venom of the Australian pygmy copperhead (Austrelaps labialis): an atypical long-chain α-neurotoxin with only weak affinity for α7 nicotinic receptors.
abstract: Despite the in vivo lethality of venom, neurotoxicity has not previously been considered a significant complication of envenoming by the Australian pygmy copperhead (Austrelaps labialis). However, recent evidence has emerged demonstrating that this venom contains potent presynaptic and postsynaptic neurotoxicity. The present study describes the isolation and pharmacological characterization of the first postsynaptic neurotoxin, α-EPTX-Al2a, from the venom of A. labialis. α-EPTX-Al2a (8072.77 Da) caused a concentration-dependent block of twitch contractions and a complete block of responses to cholinergic agonists in the chick biventer cervicis nerve-muscle preparation. This action is consistent with postjunctional neurotoxicity. Monovalent tiger snake antivenom prevented the onset of neurotoxicity if applied prior to toxin administration, but was only able to partially reverse neurotoxicity once muscle paralysis had developed. α-EPTX-Al2a produced a potent pseudo-irreversible antagonism of chick muscle nicotinic acetylcholine receptors (nAChRs), with an estimated pA(2) value of 7.902 (K(B) = 12.5 nM). Interestingly, the toxin only produced a modest block of neuronal α7 nAChRs, with an IC(50) of 1.2 μM, and failed to inhibit ganglionic α3β2/α3β4 nAChRs in a fluorescence-based FLIPR assay using SH-SY5Y cells. α-EPTX-Al2a contained 75 amino acid residues with five disulfide bonds that had significant homology to classical long-chain α-neurotoxins. While α-EPTX-Al2a retains most pharmacophore residues critical for binding to muscle-type (α1)(2)βγδ nAChRs it lacks the key Ala(28) and Arg(36) residues important for α7 nAChR affinity. Given that A. labialis venom contains both irreversible presynaptic and postsynaptic neurotoxins, clinicians need to be aware of potential neurotoxic complications associated with pygmy copperhead envenomation.
authors: Neurotoxin Research Group, Department of Medical and Molecular Biosciences, University of Technology, Sydney, PO Box 123, Broadway, NSW, 2007, Australia.
authors: Francesca
authors: F
authors: Marcon
authors: Mathieu
authors: M
authors: Leblanc
authors: Irina
authors: I
authors: Vetter
authors: Richard J
authors: RJ
authors: Lewis
authors: Pierre
authors: P
authors: Escoubas
authors: Graham M
authors: GM
authors: Nicholson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000997:Antivenins / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D045744:Cell Line, Tumor; D002645:Chickens; D003435:Crotalid Venoms / Q000737:chemistry / Q000302:isolation & purification / Q000633:toxicity*; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000187:drug effects; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D009498:Neurotoxins / Q000737:chemistry / Q000302:isolation & purification / Q000633:toxicity*; D018722:Nicotinic Agonists / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000737:chemistry / Q000302:isolation & purification / Q000633:toxicity; D054497:Phospholipases A2, Secretory / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D009435:Synaptic Transmission; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: D000997:Antivenins; D003435:Crotalid Venoms; D009498:Neurotoxins; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D011978:Receptors, Nicotinic; C575720:alpha-elapitoxin-Al2a, Austrelaps labialis; D064569:alpha7 Nicotinic Acetylcholine Receptor; D002217:Carbachol; D054497:Phospholipases A2, Secretory