Because of their key role in the transduction and transmission of nociceptive stimuli, voltage-gated sodium (NaV) channels represent an essential therapeutic target for the treatment of multiple neuropathic conditions. However, with nine Nav isoforms – each of which displays a distinct functional profile and tissue-specific expression pattern – subtype-selectivity is of the utmost importance for both research and therapeutic purposes. To date, current therapeutics targeting NaV channels critically lack subtype selectivity and as such exhibit a range of harmful side-effects.
The high specificity towards ion channels, inherent selectivity, and ability to act as gating modifiers through state-dependent interactions make spider venom peptides an excellent starting point for the engineering of selective NaV modulators. Of these, β/δ-TRTX-Pre1a was isolated from the tarantula Psalmopoeus reduncas and is part of the recently classified NaV spider toxin Family 1, sharing high sequence similarity and structural homology in the form of an inhibitory cysteine knot (ICK) motif. Pre1a exhibited neuronal selectivity and unique pharmacological characteristics, acting as a sub-micromolar inhibitor of peak current to NaV1.2 and NaV1.7 and also an inhibitor of fast inactivation for NaV1.3. Further, Pre1a demonstrated structural heterogeneity by exhibiting multiple, identifiable conformations in solution. To study the pharmacology and structure in more detail, a rational mutagenesis was pursued in combination with the standard Ala substitution. Residues of interest were decided using publicly available data on known peptides of similar sequence and function.
The work presented here details the results of functional mutations at a single residue of Pre1a, K34, and how these changes strongly affected NaV selectivity towards specific isoforms.