Peptide-membrane interactions affect the inhibitory potency and selectivity of spider toxins ProTx-II and GpTx-1

Gating modifier toxins (GMTs) from spider venom can inhibit voltage gated sodium channels (Na(V)s) involved in pain signal transmission, including the Na(V)1.7 subtype. GMTs have a conserved amphipathic structure that allow them to interact with membranes and also with charged residues in regions of Na-V that are exposed at the cell surface. ProTx-II and GpTx-1 are GMTs able to inhibit Na(V)1.7 with high potency, but they differ in their ability to bind to membranes and in their selectivity over other Na-V subtypes. To explore these differences and gain detailed information on their membrane-binding ability and how this relates to potency and selectivity, we examined previously described Na(V)1.7 potent/selective GpTx-1 analogues and new ProTx-II analogues designed to reduce membrane binding and improve selectivity for Na(V)1.7. Our studies reveal that the number and type of hydrophobic residues as well as how they are presented at the surface determine the affinity of ProTx-II and GpTx-1 for membranes and that altering these residues can have dramatic effects on Na-V inhibitory activity. We demonstrate that strong peptide-membrane interactions are not essential for inhibiting Na(V)1.7 and propose that hydrophobic interactions instead play an important role in positioning the GMT at the membrane surface proximal to exposed Na-V residues, thereby affecting peptide-channel interactions. Our detailed structure-activity relationship study highlights the challenges of designing GMT-based molecules that simultaneously achieve high potency and selectivity for Na(V)1.7, as single mutations can induce local changes in GMT structure that can have a major impact on Na-V inhibitory activity