A Buthus martensii Karsch scorpion sting targets Na(v)1.7 in mice and mimics a phenotype of human chronic pain

Gain-of-function and loss-of-function mutations in Na(v)1.7 cause chronic pain and pain insensitivity, respectively. The preferential expression of Na(v)1.7 in the peripheral nervous system and its role in human pain signaling make Na(v)1.7 a promising target for next-generation pain therapeutics. However, pharmacological agents have not fully recapitulated these pain phenotypes, and because of the lack of subtype-selective molecular modulators, the role of Na(v)1.7 in the perception of pain remains poorly understood. Scorpion venom is an excellent source of bioactive peptides that modulate various ion channels, including voltage-gated sodium (Na-v) channels. Here, we demonstrate that Buthus martensii Karsch scorpion venom (BV) elicits pain responses in mice through direct enhancement of Na(v)1.7 activity and have identified Makatoxin-3, an alpha-like toxin, as a critical component for BV-mediated effects on Na(v)1.7. Blocking other Na-v subtypes did not eliminate BV-evoked pain responses, supporting the pivotal role of Na(v)1.7 in BV-induced pain. Makatoxin-3 acts on the S3-S4 loop of voltage sensor domain IV (VSD4) of Na(v)1.7, which causes a hyperpolarizing shift in the steady-state fast inactivation and impairs inactivation kinetics. We also determined the key residues and structure-function relationships for the toxin-channel interactions, which are distinct from those of other well-studied alpha toxins. This study not only reveals a new mechanism underlying BV-evoked pain but also enriches our knowledge of key structural elements of scorpion toxins that are pivotal for toxin-Na(v)1.7 interactions, which facilitates the design of novel Na(v)1.7 selective modulators.