Addition of K22 Converts Spider Venom Peptide Pme2a from an Activator to an Inhibitor of NaV1.7.

Spider venom is a novel source of disulfide-rich peptides with potent and selective activity at voltage-gated sodium channels (NaV). Here, we describe the discovery of µ-theraphotoxin-Pme1a and µ/δ-theraphotoxin-Pme2a, two novel peptides from the venom of the Gooty Ornamental tarantula Poecilotheria metallica that modulate NaV channels. Pme1a is a 35 residue peptide that inhibits NaV1.7 peak current (IC50 334 ± 114 nM) and shifts the voltage dependence of activation to more depolarised membrane potentials (V1/2 activation: Δ = +11.6 mV). Pme2a is a 33 residue peptide that delays fast inactivation and inhibits NaV1.7 peak current (EC50 > 10 µM). Synthesis of a [+22K]Pme2a analogue increased potency at NaV1.7 (IC50 5.6 ± 1.1 µM) and removed the effect of the native peptide on fast inactivation, indicating that a lysine at position 22 (Pme2a numbering) is important for inhibitory activity. Results from this study may be used to guide the rational design of spider venom-derived peptides with improved potency and selectivity at NaV channels in the future.