Corrigendum: Pharmacological characterisation of the highly NaV1.7 selective spider venom peptide Pn3a

Evaluation of Efficient Non-reducing Enzymatic and Chemical Ligation Strategies for Complex Disulfide-Rich Peptides

Double-knotted peptides identified in venoms and synthetic bivalent peptide constructs targeting ion channels are emerging tools for the study of ion channel pharmacology and physiology. These highly complex and disulfide-rich peptides contain two individual cystine knots, each comprising six cysteines and three disulfide bonds. Until now, native double-knotted peptides, such as Hi1a and DkTx, have only been isolated from venom or produced recombinantly, whereas engineered double-knotted peptides have successfully been produced through enzymatic ligation using sortase A to form a seamless amide bond at the ligation site between two knotted toxins, and by alkyne/azide click chemistry, joining two peptide knots via a triazole linkage. To further pursue these double-knotted peptides as pharmacological tools or probes for therapeutically relevant ion channels, we sought to identify a robust methodology resulting in a high yield product that lends itself to rapid production and facile mutational studies. In this study, we evaluated the ligation efficiency of enzymatic (sortase A5°, butelase 1, wild-type OaAEP 1, C247A-OaAEP 1, and peptiligase) and mild chemical approaches (α-ketoacid-hydroxylamine, KAHA) for forming a native amide bond linking the toxins while maintaining the native disulfide connectivity of each pre-folded peptide. We used two Na_V1.7 inhibitors: PaurTx3, a spider-derived gating modifier peptide, and KIIIA, a small cone snail-derived pore blocker peptide, which have previously been shown to increase affinity and inhibitory potency on hNa_V1.7 when ligated together. Correctly folded peptides were successfully ligated in varying yields, without disulfide bond shuffling or reduction, with sortase A5° being the most efficient, resulting in 60% ligation conversion within 15 min. In addition, electrophysiology studies demonstrated that for these two peptides, the amino acid composition of the linker did not affect the activity of the double-knotted peptides. This study demonstrates the powerful application of enzymes in efficiently ligating complex disulfide-rich peptides, paving the way for facile production of double-knotted peptides.

Multiple sodium channel isoforms mediate the pathological effects of Pacific ciguatoxin-1

Human intoxication with the seafood poison ciguatoxin, a dinoflagellate polyether that activates voltage-gated sodium channels (Na_V), causes ciguatera, a disease characterised by gastrointestinal and neurological disturbances. We assessed the activity of the most potent congener, Pacific ciguatoxin-1 (P-CTX-1), on Na_V1.1–1.9 using imaging and electrophysiological approaches. Although P-CTX-1 is essentially a non-selective Na_V toxin and shifted the voltage-dependence of activation to more hyperpolarising potentials at all Na_V subtypes, an increase in the inactivation time constant was observed only at Na_V1.8, while the slope factor of the conductance-voltage curves was significantly increased for Na_V1.7 and peak current was significantly increased for Na_V1.6. Accordingly, P-CTX-1-induced visceral and cutaneous pain behaviours were significantly decreased after pharmacological inhibition of Na_V1.8 and the tetrodotoxin-sensitive isoforms Na_V1.7 and Na_V1.6, respectively. The contribution of these isoforms to excitability of peripheral C- and A-fibre sensory neurons, confirmed using murine skin and visceral single-fibre recordings, reflects the expression pattern of Na_V isoforms in peripheral sensory neurons and their contribution to membrane depolarisation, action potential initiation and propagation.