Structure-Function Elucidation of a New {alpha}-conotoxin, Lo1a, from Conus longurionis [Molecular Biophysics]

February 24th, 2014 by Lebbe, E. K. M., Peigneur, S., Maiti, M., Devi, P., Ravichandran, S., Lescrinier, E., Ulens, C., Waelkens, E., D'Souza, L., Herdewijn, P., Tytgat, J.

α-Conotoxins are peptide toxins found in the venom of marine Cone snails and potent antagonists of various subtypes of nicotinic acetylcholine receptors (nAChRs). nAChRs are cholinergic receptors forming ligand-gated ion channels in the plasma membranes of certain neurons and 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 such as epilepsy, myasthenic syndromes, schizophrenia, Parkinson′s and Alzheimer′s diseases. In order to expand the knowledge concerning Cone snail toxins, we examined the venom of Conus longurionis. We isolated an 18-amino acid peptide named α-conotoxin Lo1a, which is active on nAChRs. To the best of our knowledge, this is the first characterization of a conotoxin from this species. The peptide was characterized by electrophysiological screening against several types of cloned nAChRs expressed in Xenopus laevis oocytes. The three-dimensional solution structure of the α-conotoxin Lo1a was determined by NMR spectroscopy. Lo1a, member of the α4/7 family, blocks the response to acetylcholine in oocytes expressing α7 nAChRs with an IC50 of 3.24 ± 0.7 μM. Furthermore, Lo1a shows a high selectivity for neuronal versus muscle subtype nAChRs. As Lo1a has an unusual C-terminus, we designed two mutants, Lo1a-ΔD and Lo1a-RRR, in order to investigate the influence of the C-terminal residue. Lo1a-ΔD has a C-terminal Asp-deletion whereas in Lo1a-RRR, a triple Arg-tail replaces the Asp. They block the neuronal nAChR α7 with a lower IC50 value, but remarkably, both adopted affinity for the muscle subtype α1β1δϵ.