Molecular Description of Scorpion Toxin Interaction with Voltage-Gated Sodium Channels

Abstract

Scorpion alpha and beta toxins interact with voltage-gated sodium channels (Na v s) at two pharmacologically distinct sites. Alpha toxins bind at receptor site 3 and inhibit channel inactivation, whereas beta toxins bind at receptor site 4 and shift the voltage-dependent activation toward more hyperpolarizing potentials. The two toxin classes are subdivided to distinct pharmacological groups according to their binding preferences and competition for receptor sites at Na v subtypes. To elucidate the surface of interaction of the two toxin classes with Na v s and clarify the molecular basis of varying toxin preferences, an efficient expression system was established. Mutagenesis accompanied by toxicity, binding, and electrophysiological assays, in parallel to determination of the three-dimensional structure using NMR and X-ray crystallography, uncovered the bioactive surfaces of toxin representatives of all pharmacological groups. Exchange of external loops between channels that exhibit marked differences in sensitivity to various toxins accompanied by point mutagenesis highlighted channel determinants that play a role in toxin selectivity. These data were used in further mapping of the brain channel rNa v 1.2a receptor sites for the beta-toxin Css4 (from Centruroides suffusus suffusus) and the alpha-toxin Lqh2 (from Leiurus quinquestriatus hebraeus). On the basis of channel mutations that affected Css4 activity, the known structure of the toxin and its bioactive surface, and using the structure of a potassium channel as template, a structural model of Css4 interaction with the gating module of domain II was constructed. This initial model was the first step in the identification of part of receptor site 4. In parallel, a swapping and a mutagenesis approach employing the rNa v 1.2a mammalian and DmNa v 1 insect Na v s and the toxin Lqh2 as a probe were used to search for receptor site 3. The channel mapping along with toxin dissociation assays and double-mutant cycle analyses using toxin and channel mutants identified the gating module of domain IV as the site of interaction with the toxin core domain, thus describing the docking orientation of an alpha toxin at the channel surface.

Scorpion toxin peptide action at the ion channel subunit level

“…Previous reviews have focused on the structural, computational, and molecular analysis of scorpion venom components and ion channel interactions (Smith et al, 2014;Gurevitz et al, 2014), as well as functional comparison of their actions on ion channels. Although some reviews have outlined a broad overview of SCTX peptide action Quintero-Hernandez et al, 2013;du Plessis et al, 2008), the majority have provided relatively detailed information of SCTX action within particular ion channel subfamilies, such as sodium channels Gordon et al, 2007;Pedraza Escalona and Possani, 2013;Pucca et al, 2015a;Gilchrist and Bosmans, 2012;Gordon and Gurevitz, 2003), potassium channels MartinEauclaire and Bougis, 2012;Jimenez-Vargas et al, 2012a;Bartok et al, 2015;Yu et al, 2016;Bougis and Martin-Eauclaire, 2015;Yang et al, 2015;Wang et al, 2014;Wanke and Restano-Cassulini, 2007), and to a lesser extent, calcium Norton and McDonough, 2008;Ramos-Franco and Fill, 2016), and chloride channels Dardevet et al, 2015).…”

Colombian Scorpion Centruroides margaritatus: Purification and Characterization of a Gamma Potassium Toxin with Full-Block Activity on the hERG1 Channel

“…Scorpion venom is a mixture of proteins, peptides and enzymes, carbohydrates, free amines, nucleotides, lipids, and other low molecular weight components with unknown function. Peptides that act as ion channel modulators are the main agents responsible for the venom toxicity and they have been classified according to their targets into: sodium scorpion toxins (NaScTx), with molecular masses between 6-8 kDa [6], potassium scorpion toxins (KScTx), with molecular masses between 3-5 kDa [7,8], and calcium scorpion toxins (CaScTx) that comprise peptides acting on voltage gated calcium channels and that specifically modulate ryanodine receptors [9,10]. In the last decades, many details of the toxin-channel interaction have been clarified and models of different mechanisms of toxin binding have been described [11][12][13].…”