MmTX1 and MmTX2 from coral snake venom potently modulate GABA A receptor activity

• Published in: Proceedings of the National Academy of Sciences - PNAS 2015-02, Vol.112 (8), p.E891-E900
• Main Authors: Rosso, Jean-Pierre, Schwarz, Jürgen R., Diaz-Bustamante, Marcelo, Céard, Brigitte, Gutiérrez, José M., Kneussel, Matthias, Pongs, Olaf, Bosmans, Frank, Bougis, Pierre E.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Biochemistry; Biochemistry, Molecular Biology; Elapid Venoms; Elapidae; HEK293 Cells; Hippocampus; Humans; Ion Channel Gating; Kinetics; Life Sciences; Male; Mice; Molecular Sequence Data; Mutation; Nerve Net; Neurobiology; Neurons; Neurons and Cognition; Peptides; Protein Binding; Protein Subunits; Rats; Receptors, GABA-A; Recombinant Proteins; Synaptosomes; Xenopus
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1415488112

In this study, we report the identification of the first potent GABA A receptor-targeting toxins, to our knowledge, in snake venom, which provides a conceptual example for discovering novel ligands to study this receptor family, both functionally and structurally. Moreover, successful synthetic and recombinant production of these toxins [micrurotoxin1 (MmTX1) and MmTX2] will be valuable to further enhance their subtype selectivity or potency. In a broader context, both toxins may provide tools to evoke seizures in assays geared toward testing antiepileptic drugs or as lead molecules for designing therapeutics that modulate GABA A receptor activity. GABA A receptors shape synaptic transmission by modulating Cl − conductance across the cell membrane. Remarkably, animal toxins that specifically target GABA A receptors have not been identified. Here, we report the discovery of micrurotoxin1 (MmTX1) and MmTX2, two toxins present in Costa Rican coral snake venom that tightly bind to GABA A receptors at subnanomolar concentrations. Studies with recombinant and synthetic toxin variants on hippocampal neurons and cells expressing common receptor compositions suggest that MmTX1 and MmTX2 allosterically increase GABA A receptor susceptibility to agonist, thereby potentiating receptor opening as well as desensitization, possibly by interacting with the α + /β − interface. Moreover, hippocampal neuron excitability measurements reveal toxin-induced transitory network inhibition, followed by an increase in spontaneous activity. In concert, toxin injections into mouse brain result in reduced basal activity between intense seizures. Altogether, we characterized two animal toxins that enhance GABA A receptor sensitivity to agonist, thereby establishing a previously unidentified class of tools to study this receptor family.