title: Rational design of alpha-conotoxin analogues targeting alpha7 nicotinic acetylcholine receptors: improved antagonistic activity by incorporation of proline derivatives.
abstract: Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that belong to the superfamily of Cys loop receptors. Valuable insight into the orthosteric ligand binding to nAChRs in recent years has been obtained from the crystal structures of acetylcholine-binding proteins (AChBPs) that share significant sequence homology with the amino-terminal domains of the nAChRs. alpha-Conotoxins, which are isolated from the venom of carnivorous marine snails, selectively inhibit the signaling of neuronal nAChR subtypes. Co-crystal structures of alpha-conotoxins in complex with AChBP show that the side chain of a highly conserved proline residue in these toxins is oriented toward the hydrophobic binding pocket in the AChBP but does not have direct interactions with this pocket. In this study, we have designed and synthesized analogues of alpha-conotoxins ImI and PnIA[A10L], by introducing a range of substituents on the Pro(6) residue in these toxins to probe the importance of this residue for their binding to the nAChRs. Pharmacological characterization of the toxin analogues at the alpha(7) nAChR shows that although polar and charged groups on Pro(6) result in analogues with significantly reduced antagonistic activities, analogues with aromatic and hydrophobic substituents in the Pro(6) position exhibit moderate activity at the receptor. Interestingly, introduction of a 5-(R)-phenyl substituent at Pro(6) in alpha-conotoxin ImI gives rise to a conotoxin analogue with a significantly higher binding affinity and antagonistic activity at the alpha(7) nAChR than those exhibited by the native conotoxin.
authors.affiliation: Department of Medicinal Chemistry and Pharmaceutics and Analytical Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen Ø DK-2100, Denmark.
authors.forename: Christopher
authors.initials: C
authors.lastname: Armishaw
authors.forename: Anders A
authors.initials: AA
authors.lastname: Jensen
authors.forename: Thomas
authors.initials: T
authors.lastname: Balle
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Clark
authors.forename: Kasper
authors.initials: K
authors.lastname: Harpsøe
authors.forename: Christian
authors.initials: C
authors.lastname: Skonberg
authors.forename: Tommy
authors.initials: T
authors.lastname: Liljefors
authors.forename: Kristian
authors.initials: K
authors.lastname: Strømgaard
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002942:Circular Dichroism; D020916:Conotoxins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D015195:Drug Design; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018733:Nicotinic Antagonists / Q000737:chemistry* / Q000494:pharmacology*; D019906:Nuclear Magnetic Resonance, Biomolecular; D011392:Proline / Q000031:analogs & derivatives* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051381:Rats; D011978:Receptors, Nicotinic / Q000378:metabolism*; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: C579167:Chrna7 protein, human; C579165:Chrna7 protein, rat; D020916:Conotoxins; D018733:Nicotinic Antagonists; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D011392:Proline