Palmitoylation Affects the Interaction of Animal Toxins with Sodium Channels

Abstract

Animal toxins can interact with voltage sensor paddle motifs within voltage-activated sodium (Nav) channel voltage sensors to alter channel function. These structural motifs were originally identified in voltage-activated potassium (Kv) channels, where they were shown to move at the protein-lipid interface to drive activation of the voltage sensors and opening of the pore. Serendipitously, we identified a variant of Nav1.2 with functional properties similar to wild-type, but that exhibits a 20-fold higher apparent affinity for PaurTx3, a voltage sensor toxin isolated from tarantula venom. The amino acid difference that underlies this large divergence in toxin sensitivity was identified as G1079C and is located in the intracellular loop between domain II and domain III of the channel. Since this region is unlikely to be directly accessible to peptide toxins applied to the external solution, we explored the possibility that cysteine palmitoylation underlies this observation. When we inhibit palmitoylation of Nav1.2 and the G1079C mutant by using 2-Br-palmitate, the apparent affinities of the toxin for both channels now coincide. While surveying other molecules, we found a second tarantula toxin, ProTx-II, which is similarly influenced by Nav1.2 palmitoylation. Interestingly, both these toxins interact with the paddle motif in domain II of the channel whereas a scorpion toxin that interacts with the domain IV voltage sensor, AaHII, is not affected. These results suggest an important role for palmitoylation in shaping the pharmacological properties of Nav1.2 and have implications for changes in drug susceptibility of Nav channels caused by intracellular mutations.