A complicated complex: Ion channels, voltage sensing, cell membranes and peptide inhibitors

Abstract

Voltage-gated ion channels (VGICs) are specialised ion channels that have a voltage dependent mode of action, where ion conduction, or gating, is controlled by a voltage-sensing mechanism. VGICs are critical for electrical signalling and are therefore important pharmacological targets. Among these, voltage-gated sodium channels (Nas) have attracted particular attention as potential analgesic targets. Nas, however, comprise several structurally similar subtypes with unique localisations and distinct functions, ranging from amplification of action potentials in nociception (e.g. Na1.7) to controlling electrical signalling in cardiac function (Na1.5). Understanding the structural basis of Na function is therefore of great significance, both to our knowledge of electrical signalling and in development of subtype and state selective drugs. An important tool in this pursuit has been the use of peptides from animal venoms as selective Na modulators. In this review, we look at peptides, particularly from spider venoms, that inhibit Nas by binding to the voltage sensing domain (VSD) of this channel, known as gating modifier toxins (GMT). In the first part of the review, we look at the structural determinants of voltage sensing in VGICs, the gating cycle and the conformational changes that accompany VSD movement. Next, the modulation of the analgesic target Na1.7 by GMTs is reviewed to develop bioinformatic tools that, based on sequence information alone, can identify toxins that are likely to inhibit this channel. The same approach is also used to define VSD sequences, other than that from Na1.7, which are likely to be sensitive to this class of toxins. The final section of the review focuses on the important role of the cellular membrane in channel modulation and also how the lipid composition affects measurements of peptide-channel interactions both in binding kinetics measurements in solution and in cell-based functional assays.

The NaV1.7 Channel Subtype as an Antinociceptive Target for Spider Toxins in Adult Dorsal Root Ganglia Neurons

“…Toxins and their mutants brought a better understanding of the so-called trimolecular complex relations. Hence, the affinity of GMTs for bilayer membrane lipids highlighted the type of amino acid residues implicated in these interactions that could also impact the toxin selectivity for Na V channels ( Deplazes et al, 2016 ; Henriques et al, 2016 ; Agwa et al, 2017 , 2018 ; Zhang et al, 2018 ). Moreover, the pharmacological sensitivity of Na V channels for toxins may be modulated by PTMs on the Na V channel protein itself ( Liu et al, 2012 ).…”

Engineering Gain-of-Function Analogues of the Spider Venom Peptide HNTX-I, A Potent Blocker of the hNaV1.7 Sodium Channel

“…All these factors may affect the electrostatic properties of the peptide and change its pharmacological specificity. Furthermore, the aromatic group Trp32 strengthened hydrophobic interaction in the hydrophobic patch, and S23 was required to orient the critical Trp29 and Lys31 residues correctly [ 20 , 26 ]. Taken together, these results suggest that in addition to the highly conserved charged surface and the hydrophobic surface, less-conserved acidic residues and surrounding residues play important roles in pharmacological flexibility.…”

“…In this study, we engineered HNTX-I and explored its analogues’ inhibitory activity against established pain target hNa V 1.7. Recently, the X 1 X 2 SWCKX 3 motif, in which X stands for any hydrophobic residues and S is required to position W and K correctly, was proposed to be essential for the activity of peptides on Na V 1.7 [ 26 ]. In our study, the gain-of-function analogue E1G–N23S–D26H–L32W achieved high potency against Na V 1.7 with an IC 50 value of 0.036 ± 0.007 µM, and its structure pattern conformed to the proposed motif.…”

Introductory Chapter: Ion Channels

“…There are many different types of ion channels distributed in each cell of our body; for example, in the cells of inner ear alone, there are about 300 ion channels [22]. Ion channels are mainly classified [23,24] on the basis of the following: 3. The number of the gates.…”