Ala-7, His-10 and Arg-12 are crucial amino acids for activity of a synthetically engineered μ-conotoxin

In silico toxicology investigation of μ-conotoxin KIIIA on human Na+ channel Nav1.2

Conotoxins(CTXs) can specifically act on multiple ion channels, which are crucial for the development of neurobiology and novel targeted drug development. At present, >10,000 kinds of CTXs have been sequenced, it would be extremely laborious to conduct experiments for each. μ-CTX KIIIA is a type of substance that can selectively recognize voltage-gated sodium ion channels. This article constructs four derivatives of KIIIA and predicts their 3D structures; afterwards, their molecular orbital arrangements and physicochemical properties were calculated using DFT; then, predicted their toxicokinetic parameters such as absorption, distribution, metabolism, excretion (ADME) and toxicity (T) through Machine Learning (ML); finally, molecular docking and molecular dynamics are used to investigate the interaction modes and binding affinity. The results indicate that the toxicity of KIIIA and its derivatives (KIIIA-1 -KIIIA-4) to the human body is mainly concentrated in the liver and respiratory tract. Among four derivatives, KIIIA-2 (5 Ser → Arg) has better toxicokinetics properties and its binding energy to Nav1.2 is -65.32 kcal/mol, which is higher than that of wild type(-32.13 kcal/mol). This study indicate that computational toxicology can facilitate the druggability research of CTXs, and KIIIA-2 can be developed as a potential antiepileptic drug.

µ-Conotoxins Targeting the Human Voltage-Gated Sodium Channel Subtype NaV1.7

µ-Conotoxins are small, potent, peptide voltage-gated sodium (Na_V) channel inhibitors characterised by a conserved cysteine framework. Despite promising in vivo studies indicating analgesic potential of these compounds, selectivity towards the therapeutically relevant subtype Na_V1.7 has so far been limited. We recently identified a novel µ-conotoxin, SxIIIC, which potently inhibits human Na_V1.7 (hNa_V1.7). SxIIIC has high sequence homology with other µ-conotoxins, including SmIIIA and KIIIA, yet shows different Na_V channel selectivity for mammalian subtypes. Here, we evaluated and compared the inhibitory potency of µ-conotoxins SxIIIC, SmIIIA and KIIIA at hNa_V channels by whole-cell patch-clamp electrophysiology and discovered that these three closely related µ-conotoxins display unique selectivity profiles with significant variations in inhibitory potency at hNa_V1.7. Analysis of other µ-conotoxins at hNa_V1.7 shows that only a limited number are capable of inhibition at this subtype and that differences between the number of residues in loop 3 appear to influence the ability of µ-conotoxins to inhibit hNa_V1.7. Through mutagenesis studies, we confirmed that charged residues in this region also affect the selectivity for hNa_V1.4. Comparison of µ-conotoxin NMR solution structures identified differences that may contribute to the variance in hNa_V1.7 inhibition and validated the role of the loop 1 extension in SxIIIC for improving potency at hNa_V1.7, when compared to KIIIA. This work could assist in designing µ-conotoxin derivatives specific for hNa_V1.7.

Where cone snails and spiders meet: design of small cyclic sodium-channel inhibitors

A 13 aa residue voltage-gated sodium (Na_V) channel inhibitor peptide, Pn, containing 2 disulfide bridges was designed by using a chimeric approach. This approach was based on a common pharmacophore deduced from sequence and secondary structural homology of 2 Na_V inhibitors: Conus kinoshitai toxin IIIA, a 14 residue cone snail peptide with 3 disulfide bonds, and Phoneutria nigriventer toxin 1, a 78 residue spider toxin with 7 disulfide bonds. As with the parent peptides, this novel Na_V channel inhibitor was active on Na_V1.2. Through the generation of 3 series of peptide mutants, we investigated the role of key residues and cyclization and their influence on Na_V inhibition and subtype selectivity. Cyclic PnCS1, a 10 residue peptide cyclized via a disulfide bond, exhibited increased inhibitory activity toward therapeutically relevant Na_V channel subtypes, including Na_V1.7 and Na_V1.9, while displaying remarkable serum stability. These peptides represent the first and the smallest cyclic peptide Na_V modulators to date and are promising templates for the development of toxin-based therapeutic agents.-Peigneur, S., Cheneval, O., Maiti, M., Leipold, E., Heinemann, S. H., Lescrinier, E., Herdewijn, P., De Lima, M. E., Craik, D. J., Schroeder, C. I., Tytgat, J. Where cone snails and spiders meet: design of small cyclic sodium-channel inhibitors.

Crotalus durissus terrificus crotapotin naturally displays preferred positions for amino acid substitutions

Background

Classically, Crotalus durissus terrificus (Cdt) venom can be described, according to chromatographic criteria, as a simple venom, composed of four major toxins, namely: gyroxin, crotamine, crotoxin and convulxin. Crotoxin is a non-covalent heterodimeric neurotoxin constituted of two subunits: an active phospholipase A₂ and a chaperone protein, termed crotapotin. This molecule is composed of three peptide chains connected by seven disulfide bridges. Naturally occurring variants/isoforms of either crotoxin or crotapotin itself have already been reported.

Methods

The crude Cdt venom was separated by using RP-HPLC and the toxins were identified by mass spectrometry (MS). Crotapotin was purified, reduced and alkylated in order to separate the peptide chains that were further analyzed by mass spectrometry and de novo peptide sequencing.

Results

The RP-HPLC profile of the isolated crotapotin chains already indicated that the α chain would present isoforms, which was corroborated by the MS and tandem mass spectrometry analyses.

Conclusion

It was possible to observe that the Cdt crotapotin displays a preferred amino acid substitution pattern present in the α chain, at positions 31 and 40. Moreover, substitutions could also be observed in β and γ chains (one for each). The combinations of these four different peptides, with the already described chains, would produce ten different crotapotins, which is compatible to our previous observations for the Cdt venom.