Venom Peptides Across Asian and American Tarantulas Utilize Dual Pharmacology to Target Activation and Fast Inactivation of Voltage-Gated Sodium Channels

Spider-derived venoms are a rich source of cystine knot peptides with immense therapeutic potential. Many of these peptides exert unique biological activities through the modulation of ion channels, including of human voltage-gated sodium (Na_V1.1-Na_V1.9) channels. Na_V channel subtypes have diverse functions determined by their tissue and cellular distribution and biophysical properties, and are pathophysiology mediators in various diseases. Therefore, Na_Vs are central in studies of human biology. This work investigated the pharmacological properties of venom of the Thai theraphosid <i>Ornithoctonus aureotibialis</i> on Na_V channels. We discovered a predominant venom peptide named Oa1a and assessed its pharmacological properties across human Na_V channel subtypes. Synthetic forms of the peptide Oa1a showed preferential inhibition of Na_V1.1 and Na_V1.7, while recombinant Oa1a displayed a preference for inhibiting Na_V1.2, Na_V1.6, and Na_V1.7. Interestingly, all versions of Oa1a peptides exerted dual pharmacological effect by reducing the peak current and slowing fast inactivation of Na_V1.3, consistent with Oa1a having more than one binding site on Na_V channels. Such complex pharmacology was previously observed for a venom peptide in a Central American and Costa Rican tarantula, suggesting a conserved mechanism of action amongst these geographically distinct species. However, Oa1a lacked activity in the T-type channels observed in the tarantula peptide from Central America. Structure-function relationships investigated using molecular modelling showed that the dual pharmacology is driven by a conserved mechanism utilizing a mix of aromatic and charged residues, while the T-type activity appears to require additional charged residues in loop 2 and fewer positive charges in loop 4. Future structure-activity relationship studies of Oa1a will guide the development of pharmacological tools as well as next-generation drugs to treat Na_V channel dysfunction associated with neurological disorders.