TY - JOUR AB - In contrast to all classical long-chain ?-neurotoxins possessing the critical fifth disulfide bond, ?-elapitoxin-Aa2a (?-EPTX-Aa2a), a novel long-chain ?-neurotoxin from the common death adder Acanthophis antarcticus, lacks affinity for neuronal ?7-type nicotinic acetylcholine receptors (nAChRs) ?-EPTX-Aa2a (8850 Da; 0.1-1 ?M) caused a concentration-dependent inhibition of indirect twitches, and blocked contractures to cholinergic agonists in the isolated chick biventer cervicis nerve-muscle preparation, consistent with a postsynaptic curaremimetic mode of action. ?-EPTX-Aa2a (1-10 nM) produced a potent pseudo-irreversible antagonism of chick muscle nAChRs, with an estimated pA2 value of 8.311 ± 0.031, which was not reversed by monovalent death adder antivenom. This is only 2.5-fold less potent than the prototypical long-chain ?-neurotoxin, ?-bungarotoxin. In contrast, ?-EPTX-Aa2a produced complete, but weak, inhibition of 125I-?-bungarotoxin binding to rat hippocampal ?7 nAChRs (pKI = 3.670), despite high sequence homology and similar mass to a wide range of long-chain ?-neurotoxins. The mostly likely cause for the loss of ?7 binding affinity is a leucine substitution, in loop II of ?-EPTX-Aa2a, for the highly conserved Arg33 in long-chain ?-neurotoxins. Arg 33 has been shown to be critical for both neuronal and muscle activity. Despite this substitution, ?-EPTX-Aa2a retains high affinity for muscle (?1)2??? nAChRs. This is probably as a result of an Arg29 residue, previously shown to be critical for muscle (?1)2??? nAChR affinity, and highly conserved across all short-chain, but not long-chain, ?-neurotoxins. ?-EPTX-Aa2a therefore represents a novel atypical long-chain ?-neurotoxin that includes a fifth disulfide but exhibits differential affinity for nAChR subtypes. Copyright © 2010 Published by Elsevier Inc. All rights reserved. AU - Blacklow, B AU - Kornhauser, R AU - Hains, PG AU - Loiacono, R AU - Escoubas, P AU - Graudins, A AU - Nicholson, GM DA - 2011/01/15 DO - 10.1016/j.bcp.2010.10.004 EP - 325 JO - Biochemical Pharmacology PY - 2011/01/15 SP - 314 TI - ?-Elapitoxin-Aa2a, a long-chain snake ?-neurotoxin with potent actions on muscle (?1)2??? nicotinic receptors, lacks the classical high affinity for neuronal ?7 nicotinic receptors VL - 81 Y1 - 2011/01/15 Y2 - 2024/03/29 ER -