Structural interactions of a voltage sensor toxin with lipid membranes

Abstract

Protein toxins from tarantula venom alter the activity of diverse ion channel proteins, including voltage, stretch, and ligandactivated cation channels. Although tarantula toxins have been shown to partition into membranes, and the membrane is thought to play an important role in their activity, the structural interactions between these toxins and lipid membranes are poorly understood. Here, we use solid-state NMR and neutron diffraction to investigate the interactions between a voltage sensor toxin (VSTx1) and lipid membranes, with the goal of localizing the toxin in the membrane and determining its influence on membrane structure. Our results demonstrate that VSTx1 localizes to the headgroup region of lipid membranes and produces a thinning of the bilayer. The toxin orients such that many basic residues are in the aqueous phase, all three Trp residues adopt interfacial positions, and several hydrophobic residues are within the membrane interior. One remarkable feature of this preferred orientation is that the surface of the toxin that mediates binding to voltage sensors is ideally positioned within the lipid bilayer to favor complex formation between the toxin and the voltage sensor.voltage sensor toxin | voltage-activated ion channel | toxin-membrane interaction | membrane structure | neutron diffraction P rotein toxins from venomous organisms have been invaluable tools for studying the ion channel proteins they target. For example, in the case of voltage-activated potassium (Kv) channels, pore-blocking scorpion toxins were used to identify the pore-forming region of the channel (1, 2), and gating modifier tarantula toxins that bind to S1-S4 voltage-sensing domains have helped to identify structural motifs that move at the protein-lipid interface (3-5). In many instances, these toxin-channel interactions are highly specific, allowing them to be used in target validation and drug development (6-8).Tarantula toxins are a particularly interesting class of protein toxins that have been found to target all three families of voltageactivated cation channels (3, 9-12), stretch-activated cation channels (13-15), as well as ligand-gated ion channels as diverse as acid-sensing ion channels (ASIC) (16-21) and transient receptor potential (TRP) channels (22, 23). The tarantula toxins targeting these ion channels belong to the inhibitor cystine knot (ICK) family of venom toxins that are stabilized by three disulfide bonds at the core of the molecule (16,17,(24)(25)(26)(27)(28)(29)(30)(31). Although conventional tarantula toxins vary in length from 30 to 40 aa and contain one ICK motif, the recently discovered double-knot toxin (DkTx) that specifically targets TRPV1 channels contains two separable lobes, each containing its own ICK motif (22, 23).One unifying feature of all tarantula toxins studied thus far is that they act on ion channels by modifying the gating properties of the channel. The best studied of these are the tarantula toxins targeting voltage-activated cation channels, where the toxins bind to the S3b-S4 vol...

Using voltage‐sensor toxins and their molecular targets to investigate NaV1.8 gating

“…One hypothesis for the lack of such peptides may be that nature found it more impactful to target VSDI, II, or IV to alter Na V channel function. Alternatively, toxin access to the VSDIII S3b-S4 region may be hampered by local lipid environment constraints (Lee & MacKinnon, 2004;Swartz, 2008;Milescu et al 2009;Mihailescu et al 2014;Gupta et al 2015). To circumvent this resource gap, we employed TsVII which binds to VSDII, III and IV in Na V 1.2 to hyperpolarize channel activation-voltage threshold while inhibiting current at depolarized voltages (Bosmans et al 2008).…”

Interaction of Tarantula Venom Peptide ProTx-II with Lipid Membranes Is a Prerequisite for Its Inhibition of Human Voltage-gated Sodium Channel NaV1.7

“…3, A and B, and Table 2). Although phospholipids containing the negatively charged phosphoglycerol (PG) headgroups are not common in mammalian cells (32), mixtures containing a high proportion of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) are commonly used in studies characterizing peptide-membrane interactions of similar peptide toxins (19,23,25,36,37). Thus, to examine the binding affinity for a highly negatively charged membrane and to see whether there is preference for a specific negatively charged phospholipid headgroup (i.e.…”

“…This hypothesis is supported by the typical amphipathic structure of GMTs that display positively charged amino acid residues and a hydrophobic patch at the surface of the molecule, properties common to many membrane-active venom peptides (19). Studies of GMTs isolated from tarantula, such as hanatoxin (18,20), ProTx-II (16,21), VSTx1 (19,22,23), and SGTx1 (18,24) have demonstrated their affinity for lipid bilayers, further supporting a mechanism in which the peptide gains access to its binding site via partitioning into the membrane. Nevertheless, other GMTs such as huwentoxin-IV (25) and Hd1a (26) do not show affinity for model membranes, suggesting that the ability to bind to lipid bilayers is not an obligate requirement to be a GMT (26 -28).…”

Studies of model biological and bio-mimetic membrane structure: Reflectivity vs diffraction, a critical comparison

“…Work by Boggara et al [22] looked at the location of the non-steroidal anti-inflammatory drug, ibuprofen, in lipid membranes, exploring how interaction of the drug with cell membranes might explain its gastro-intestinal toxicity. There are studies too that were concerned with the localisation within membranes of the anaesthetics halothane and dichlorohexfluorocyclobutane [23], the anti-bacterial agent, chlorhexidine [24], various antimicrobial peptides [25][26], membrane translocating peptides [27], and a spider peptide toxin [28].…”