Neurotoxin Research Group, Department of Medical & Molecular Biosciences, University of Technology, Sydney, P.O. Box 123, Broadway, NSW 2007, Australia.
Biochem Pharmacol. 2011 Jan 15;81(2):314-25. doi: 10.1016/j.bcp.2010.10.004. Epub 2010 Oct 13.
In contrast to all classical long-chain α-neurotoxins possessing the critical fifth disulfide bond, α-elapitoxin-Aa2a (α-EPTX-Aa2a), a novel long-chain α-neurotoxin from the common death adder Acanthophis antarcticus, lacks affinity for neuronal α7-type nicotinic acetylcholine receptors (nAChRs). α-EPTX-Aa2a (8850Da; 0.1-1μM) 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. α-EPTX-Aa2a (1-10nM) produced a potent pseudo-irreversible antagonism of chick muscle nAChRs, with an estimated pA(2) 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 α-neurotoxin, α-bungarotoxin. In contrast, α-EPTX-Aa2a produced complete, but weak, inhibition of (125)I-α-bungarotoxin binding to rat hippocampal α7 nAChRs (pK(I)=3.670), despite high sequence homology and similar mass to a wide range of long-chain α-neurotoxins. The mostly likely cause for the loss of α7 binding affinity is a leucine substitution, in loop II of α-EPTX-Aa2a, for the highly conserved Arg(33) in long-chain α-neurotoxins. Arg(33) has been shown to be critical for both neuronal and muscle activity. Despite this substitution, α-EPTX-Aa2a retains high affinity for muscle (α1)(2)βγδ nAChRs. This is probably as a result of an Arg(29) residue, previously shown to be critical for muscle (α1)(2)βγδ nAChR affinity, and highly conserved across all short-chain, but not long-chain, α-neurotoxins. α-EPTX-Aa2a therefore represents a novel atypical long-chain α-neurotoxin that includes a fifth disulfide but exhibits differential affinity for nAChR subtypes.
与所有具有关键第五个二硫键的经典长链α-神经毒素相反，新型长链α-神经毒素α-埃帕利托毒素-Aa2a（α-EPTX-Aa2a）来自常见的死亡 adder Acanthophis antarcticus，对神经元α7 型烟碱型乙酰胆碱受体（nAChRs）没有亲和力。α-EPTX-Aa2a（8850Da；0.1-1μM）浓度依赖性抑制间接抽搐，并阻断分离的小鸡双颈椎神经-肌肉制剂中胆碱能激动剂引起的收缩，这与突触后拟除虫菊酯样作用模式一致。α-EPTX-Aa2a（1-10nM）对小鸡肌肉 nAChRs 产生强烈的假性不可逆拮抗作用，估计 pA（2）值为 8.311±0.031，而单价死亡 adder 抗蛇毒血清不能逆转。这仅比典型的长链α-神经毒素α-银环蛇毒素弱 2.5 倍。相比之下，α-EPTX-Aa2a 对（125）I-α-银环蛇毒素与大鼠海马α7 nAChRs 的结合产生完全但较弱的抑制作用（pK（I）=3.670），尽管序列同源性高且质量相似广泛的长链α-神经毒素。失去α7 结合亲和力的最可能原因是α-EPTX-Aa2a 中 loop II 中的亮氨酸取代了长链α-神经毒素中的高度保守的 Arg（33）。Arg（33）已被证明对神经元和肌肉活动都很关键。尽管发生了这种取代，α-EPTX-Aa2a 仍保持对肌肉（α1）（2）βγδ nAChRs 的高亲和力。这可能是由于之前被证明对肌肉（α1）（2）βγδ nAChR 亲和力至关重要的 Arg（29）残基，并且在所有短链但不是长链α-神经毒素中高度保守。因此，α-EPTX-Aa2a 代表一种新型的非典型长链α-神经毒素，它包含第五个二硫键，但对 nAChR 亚型表现出不同的亲和力。
