Addition of K22 converts spider venom peptide Pme2a from an activator to an inhibitor of Na_V1.7

Spider venom is a novel source of disulfide-rich peptides with potent and selective activity at voltage-gated sodium channels (Na_V). 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 Na_V channels. Pme1a is a 35 residue peptide that inhibits Na_V1.7 peak current (IC₅₀ 334 ± 114 nM) and shifts the voltage dependence of activation to more depolarised membrane potentials (V_1/2 activation: Δ =+11.6 mV). Pme2a is a 33 residue peptide that delays fast inactivation and inhibits Na_V1.7 peak current (EC₅₀ > 10 μM). Synthesis of a [+22K]Pme2a analogue increased potency at Na_V1.7 (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 Na_V channels in the future.