A dynamic pharmacophore drives the interaction between Psalmotoxin-1 and the putative drug target acid-sensing ion channel 1a

• Published in: Molecular pharmacology Vol. 80; no. 5; pp. 796 - 808
• Main Authors: Saez, Natalie J, Mobli, Mehdi, Bieri, Michael, Chassagnon, Irène R, Malde, Alpeshkumar K, Gamsjaeger, Roland, Mark, Alan E, Gooley, Paul R, Rash, Lachlan D, King, Glenn F
• Format: Journal Article
• Language: English
• Published: United States 01.11.2011
• Subjects: Acid Sensing Ion Channels; Amino Acid Sequence; Chromatography, Affinity; Electrophoresis, Polyacrylamide Gel; Models, Molecular; Molecular Dynamics Simulation; Molecular Sequence Data; Nerve Tissue Proteins - antagonists & inhibitors; Nerve Tissue Proteins - chemistry; Nuclear Magnetic Resonance, Biomolecular; Peptides; Point Mutation; Recombinant Proteins - genetics; Recombinant Proteins - pharmacology; Sequence Homology, Amino Acid; Sodium Channels - chemistry; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Spider Venoms - chemistry; Spider Venoms - genetics; Spider Venoms - pharmacology
• ISSN: 0026-895X; 1521-0111
• DOI: 10.1124/mol.111.072207

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.