Interaction of gating-modifier tarantula toxins with voltage-gated sodium channels.

Abstract

Voltage-gated ion channels are membrane protein complexes. They allow the selective flow of their respective ions down an electrochemical gradient through a central ion conduction pore surrounded by four voltage sensing domains (VSDs). Gating-modifier toxins (GMTs) are peptide toxins found in different animal venoms that bind to these VSDs and change their gating properties. Our laboratory has determined that the GMT GsAF2, from the Chilean rose tarantula Grammostola rosea, binds to the VSD of the bacterial sodium channel NaChBac (called BHVSD). GsAF2, VSTx2 (another gating modifier toxin - the W residue at the C-terminus of GsAF2 is replaced by EG in VSTx2), and VSTx2-T8S have been synthesized recombinantly and their functionality has been tested through Automated Patch Clamp electrophysiology. Docking studies have been performed with a homology model of GsAF2 and the Cryo-EM structure of NaChBac to identify residues of the toxin and channel that could be involved in the interaction and guiding the design of suitable mutants to validate these interactions. The docked models were evaluated based on the presence of realistic and chemically feasible interactions. The best docked model based on these parameters will be energy-minimized in a membrane bilayer by molecular dynamics simulation. 15N-labeled GsAF2 has also been generated to perform Nuclear Magnetic Resonance (NMR) experiments for structure determination and to identify toxin residues involved in channel binding.