Abstract

Scorpion α-toxins are small proteins inhibiting the inactivation of voltage-gated sodium channels. They can selectively act on either mammalian (mammal toxins) or insect channels (insect toxins), or affect both types of channels (α-like toxins). Currently no model has been proposed that fully explains the dependence of selectivity upon amino acid sequence, but some patterns have already been established. Thus, most mammal toxins have an aspartic acid residue in position 8, which is involved in the formation of the nest motif, but it is still not clear whether this residue interacts directly with channels. The objective of our study was to obtain a derivative of the α-like toxin BeM9 with the replacement of lysine in position 8 by glutamate (K8E), changing the charge, but excluding the formation of the nest motif. In addition, we replaced the tyrosine in position 17 with glycine (Y17G), which is characteristic of mammal toxins. Surprisingly, the double-mutant derivative BeM9^EG lost its activity on mammalian channels, becoming an insect toxin. To explain these changes, we constructed models of BeM9 and BeM9^EG complexes with channels, and also performed molecular dynamics of isolated toxins. Analysis of intermolecular contacts in the complexes did not explain the reason for the selectivity change. Nevertheless, the structure of intramolecular contacts and data on molecular mobility indicate an important role of residues K8 and Y17 in stabilizing a certain conformation of BeM9 loops. We assume that the replacement of these residues allosterically affects the efficiency of toxin binding to channels.

中文翻译：

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蝎子神经毒素 BeM9 的衍生物对昆虫电压门控钠通道具有选择性

摘要

Scorpion α-毒素是抑制电压门控钠通道失活的小蛋白质。它们可以选择性地作用于哺乳动物（哺乳动物毒素）或昆虫通道（昆虫毒素），或影响两种类型的通道（α 样毒素）。目前还没有提出模型来完全解释选择性对氨基酸序列的依赖性，但已经建立了一些模式。因此，大多数哺乳动物毒素在第 8 位有一个天冬氨酸残基，这与巢基序的形成有关，但尚不清楚该残基是否直接与通道相互作用。我们研究的目的是获得 α 样毒素 BeM9 的衍生物，其中 8 位赖氨酸被谷氨酸 (K8E) 取代，改变电荷，但不包括巢基序的形成。此外，我们用甘氨酸 (Y17G) 替换了第 17 位的酪氨酸，这是哺乳动物毒素的特征。令人惊讶的是，双突变衍生物 BeM9^EG失去了对哺乳动物通道的活性，成为一种昆虫毒素。为了解释这些变化，我们构建了带有通道的 BeM9 和 BeM9 ^EG复合物模型，并进行了分离毒素的分子动力学分析。复合物中分子间接触的分析没有解释选择性变化的原因。尽管如此，分子内接触的结构和分子迁移率的数据表明，残基 K8 和 Y17 在稳定 BeM9 环的某些构象方面起着重要作用。我们假设这些残基的替换会变构地影响毒素与通道结合的效率。