title: A dynamic pharmacophore drives the interaction between Psalmotoxin-1 and the putative drug target acid-sensing ion channel 1a.
abstract: Acid-sensing ion channel 1a (ASIC1a) is a primary acid sensor in the peripheral and central nervous system. It has been implicated as a novel therapeutic target for a broad range of pathophysiological conditions including pain, ischemic stroke, depression, and autoimmune diseases such as multiple sclerosis. The only known selective blocker of ASIC1a is π-TRTX-Pc1a (PcTx1), a disulfide-rich 40-residue peptide isolated from spider venom. π-TRTX-Pc1a is an effective analgesic in rodent models of acute pain and it provides neuroprotection in a mouse model of ischemic stroke. Thus, understanding the molecular basis of the π-TRTX-Pc1a-ASIC1a interaction should facilitate development of therapeutically useful ASIC1a blockers. We therefore developed an efficient bacterial expression system to produce a panel of π-TRTX-Pc1a mutants for probing structure-activity relationships as well as isotopically labeled toxin for determination of its solution structure and dynamics. We demonstrate that the toxin pharmacophore resides in a β-hairpin loop that was revealed to be mobile over a wide range of time scales using molecular dynamics simulations in combination with NMR spin relaxation and relaxation dispersion measurements. The toxin-receptor interaction was modeled by in silico docking of the toxin structure onto a homology model of rat ASIC1a in a restraints-driven approach that was designed to take account of the dynamics of the toxin pharmacophore and the consequent remodeling of side-chain conformations upon receptor binding. The resulting model reveals new insights into the mechanism of action of π-TRTX-Pc1a and provides an experimentally validated template for the rational design of therapeutically useful π-TRTX-Pc1a mimetics.
authors.affiliation: Institute for Molecular Bioscience, University of Queensland, 306 Carmody Road, St Lucia, QLD 4072, Australia.
authors.forename: Natalie J
authors.initials: NJ
authors.lastname: Saez
authors.forename: Mehdi
authors.initials: M
authors.lastname: Mobli
authors.forename: Michael
authors.initials: M
authors.lastname: Bieri
authors.forename: Irène R
authors.initials: IR
authors.lastname: Chassagnon
authors.forename: Alpeshkumar K
authors.initials: AK
authors.lastname: Malde
authors.forename: Roland
authors.initials: R
authors.lastname: Gamsjaeger
authors.forename: Alan E
authors.initials: AE
authors.lastname: Mark
authors.forename: Paul R
authors.initials: PR
authors.lastname: Gooley
authors.forename: Lachlan D
authors.initials: LD
authors.lastname: Rash
authors.forename: Glenn F
authors.initials: GF
authors.lastname: King
mesh_terms: D062565:Acid Sensing Ion Channels; D000595:Amino Acid Sequence; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides; D017354:Point Mutation; D011994:Recombinant Proteins / Q000235:genetics / Q000494:pharmacology; D017386:Sequence Homology, Amino Acid; D015222:Sodium Channels / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013111:Spider Venoms / Q000737:chemistry / Q000235:genetics / Q000494:pharmacology*
chemical_list: C568267:ASIC1 protein, mouse; D062565:Acid Sensing Ion Channels; D009419:Nerve Tissue Proteins; C413209:PcTX1 protein, Psalmopoeus cambridgei; D010455:Peptides; D011994:Recombinant Proteins; D015222:Sodium Channels; D013111:Spider Venoms