Characterization and structure elucidation of an α-conotoxin Lo1a from Conus longurionis
XI Congress of the Pan-American Section of the International Society on Toxinology. XII Congress of the Brazilian Society of Toxinology Envenomation by poisonous animals: a neglected disease. edition:11 location:Sao Paulo date:03/11/2013- 08/11/2013
Introduction: α-Conotoxins are small peptide toxins that are found in the venom of marine snails, Conus, and are extremely potent antagonists against various subtypes of nicotinic acetylcholine receptors (nAChRs). nAChRs are cholinergic receptors that form ligand-gated ion channels in the plasma membranes of certain neurons and on the postsynaptic side of the neuromuscular junction. As nAChRs have an important role in regulating transmitter release, cell excitability, and neuronal integration, nAChR dysfunctions have been implicated in a variety of severe pathologies like epilepsy, myasthenic syndromes, schizophrenia and Parkinson’s and Alzheimer’s diseases. In order to expand the knowledge about Cone snail toxins, we examined the venom of an unknown Conus species, Conus longurionis. This is the first time that a conotoxin from this species was investigated. Methods and Results: This study covers the isolation of an 18-amino acid peptide from the venom of the marine snail Conus longurionis that is active on nAChRs. The peptide, named α-conotoxin Lo1a, was characterized by electrophysiological screening against several types of cloned nicotinic receptors expressed in Xenopus laevis oocytes. The toxin blocks the response to acetylcholine in oocytes expressing α7 nAChRs with an IC50 of 3.25 ± 0.7 µM, which is an important channel target in brain disorders. Also α3β4 was found to be blocked with a percentage of 40% at 10 µM. Furthermore, Lo1a shows a high selectivity for neuronal versus muscle subtype. Moreover, the three-dimensional solution structure of the α-conotoxin Lo1a was determined by NMR spectroscopy. The NMR structure reveals that the peptide backbone adopts a compact “W-shaped” conformation having two loops that are reinforced by two disulfide bonds (Cys3-Cys9 and Cys4-Cys17). Residues form Pro7 to Asn12 at the bottom of the “W-shape” formed an α-helix involving two-turns. Conclusion: Our findings provide insight into the assembly, structure and activity of an α-contoxin Lo1a that targets preferably α7-nAChR. In this way, our study contributes to the discovery of new ligands to affect brain disorders including schizophrenia, Alzheimer’s disease, traumatic brain injury and ADHD.