Three Peptide Modulators of the Human Voltage-Gated Sodium Channel 1.7, an Important Analgesic Target, from the Venom of an Australian Tarantula

Voltage-gated sodium (Na(V)) channels are responsible for propagating action potentials in excitable cells. Na(V)1.7 plays a crucial role in the human pain signalling pathway and it is an important therapeutic target for treatment of chronic pain. Numerous spider venom peptides have been shown to modulate the activity of Na(V) channels and these peptides represent a rich source of research tools and therapeutic lead molecules. The aim of this study was to determine the diversity of Na(V)1.7-active peptides in the venom of an Australian Phlogius sp. tarantula and to characterise their potency and subtype selectivity. We isolated three novel peptides, μ-TRTX-Phlo1a, -Phlo1b and -Phlo2a, that inhibit human Na(V)1.7 (hNa(V)1.7). Phlo1a and Phlo1b are 35-residue peptides that differ by one amino acid and belong in NaSpTx family 2. The partial sequence of Phlo2a revealed extensive similarity with ProTx-II from NaSpTx family 3. Phlo1a and Phlo1b inhibit hNa(V)1.7 with IC(50) values of 459 and 360 nM, respectively, with only minor inhibitory activity on rat Na(V)1.2 and hNa(V)1.5. Although similarly potent at hNa(V)1.7 (IC(50) 333 nM), Phlo2a was less selective, as it also potently inhibited rNa(V)1.2 and hNa(V)1.5. All three peptides cause a depolarising shift in the voltage-dependence of hNa(V)1.7 activation.