Gating modifier toxins isolated from spider venom: Modulation of voltage-gated sodium channels and the role of lipid membranes

Christina I Schroeder,David J Craik,Chun Yuen Chow,Akello J Agwa,Glenn F King,Jan Tytgat,Steve Peigneur,Nicole Lawrence,Sónia Troeira Henriques

doi:10.1074/jbc.ra118.002553

Christina I Schroeder, David J Craik + Show 7 more

Open Access

https://doi.org/10.1074/jbc.ra118.002553

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Abstract

Gating modifier toxins (GMTs) are venom-derived peptides isolated from spiders and other venomous creatures and modulate activity of disease-relevant voltage-gated ion channels and are therefore being pursued as therapeutic leads. The amphipathic surface profile of GMTs has prompted the proposal that some GMTs simultaneously bind to the cell membrane and voltage-gated ion channels in a trimolecular complex. Here, we examined whether there is a relationship among spider GMT amphipathicity, membrane binding, and potency or selectivity for voltage-gated sodium (NaV) channels. We used NMR spectroscopy and in silico calculations to examine the structures and physicochemical properties of a panel of nine GMTs and deployed surface plasmon resonance to measure GMT affinity for lipids putatively found in proximity to NaV channels. Electrophysiology was used to quantify GMT activity on NaV1.7, an ion channel linked to chronic pain. Selectivity of the peptides was further examined against a panel of NaV channel subtypes. We show that GMTs adsorb to the outer leaflet of anionic lipid bilayers through electrostatic interactions. We did not observe a direct correlation between GMT amphipathicity and affinity for lipid bilayers. Furthermore, GMT-lipid bilayer interactions did not correlate with potency or selectivity for NaVs. We therefore propose that increased membrane binding is unlikely to improve subtype selectivity and that the conserved amphipathic GMT surface profile is an adaptation that facilitates simultaneous modulation of multiple NaVs.

Highlights

IntroductionGating modifier toxins (GMTs) alter the gating kinetics of voltage-gated ion channels [4], which are transmembrane proteins integral to a range of physiological processes in humans [1, 5, 6]
We examined the extent to which nine Gating modifier toxins (GMTs) bound to a series of model membranes, whether there is a relationship between membrane binding and inhibition of NaV1.7, and whether GMT amphipathicity is important for membrane binding and/or inhibition of NaV channels
The pharmacology of some voltage-gated ion channels has previously shown sensitivity to the enzymatic conversion of SM to C1P by sphingomyelinase D (SMase D) [35, 36]; it is possible that sicariid spiders take advantage of the presence of SMase D, and perhaps additional venom components, to increase GMT binding to both cell membranes and the voltage-gated ion channels to optimize activity [38]

Summary

Introduction

GMTs alter the gating kinetics of voltage-gated ion channels [4], which are transmembrane proteins integral to a range of physiological processes in humans [1, 5, 6]. These GMTs contain six Cys residues arranged to form an inhibitory cystine knot motif [7]. The objective of the current study was to determine whether there is an overall relationship between the amphipathic surface profile of GMTs and their ability to bind lipid membranes and modulate voltage-gated ion channels. Previous reports have examined lipid-binding properties of small GMT cohorts [10, 11, 17, 18], but the current study represents the first concerted effort to study the membrane binding of a cohort of native GMTs in model membranes chosen to mimic physiological properties [15]

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