Beta-Pompilidotoxin Adopts a Distinct 3D Structure when Bound to Nav1.2 DIV S3-S4 Paddle Motif

Abstract

Beta-pompilidotoxin (β-PMTX) is a spider wasp toxin which binds on neurotoxin receptor site 3 of neuronal sodium channels. Even though it lacks disulfide bonds and has no structural homology to the α-scorpion toxins and sea anemone toxins that bind at the same site, β-PMTX not only slows inactivation of voltage-gated sodium channels, it also has a high affinity for Nav1.2, but does not affect Nav1.5. Due to its high specificity for Nav1.2 DIV, structural analysis of this 13 amino acid peptide may prove vital in understanding gating mechanism of the channel, because it potentially allows for the channel protein to be “locked” into a specific gating state, thus enabling future studies of the various Nav1.2 channel conformations involved in the gating mechanism. Structural analysis of β-PMTX may also provide valuable insight for the development of future pharmaceutical agents. β-PMTX was synthesized and structures were elucidated using solution state 2D homonuclear NMR. Interestingly, β-PMTX appears to be unfolded in an aqueous environment, but in the presence of a membrane mimetic and a membrane mimetic containing a Nav1.2 fragment, β-PMTX adopted two distinct 3D conformations. Characterization and elucidation of β-PMTX structure were performed in both detergent micelles and lipid bicelles, and interacting residues were identified.