Abstract
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(V)1.1-Na(V)1.9) 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(V)s are central in studies of human biology. This work investigated the pharmacological properties of venom of the Thai theraphosid Ornithoctonus aureotibialis 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(V)1.1 and Na(V)1.7, while recombinant Oa1a displayed a preference for inhibiting Na(V)1.2, Na(V)1.6, and Na(V)1.7. Interestingly, all versions of Oa1a peptides exerted dual pharmacological effect by reducing the peak current and slowing fast inactivation of Na(V)1.3, 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.