Marine Macrocyclic Imines, Pinnatoxins A and G: Structural Determinants and Functional Properties to Distinguish Neuronal α7 from Muscle α12βγδ nAChRs

• DOI: 10.1016/j.str.2015.04.009
• Publication Date: 2015-05-21T20:18:51Z
• Authors: Yves Bourne; Gerlind Sulzenbacher; Zoran Radić; Rómulo Aráoz; Morgane Reynaud; Evelyne Benoit; Armen Zakarian; Denis Servent; Jordi Molgó; Palmer Taylor; Pascale Marchot
• Keywords: Models, Molecular; 570; Macrocyclic Compounds; Patch-Clamp Techniques; alpha7 Nicotinic Acetylcholine Receptor; Protein Conformation; [SDV.NEU.NB]Life Sciences [q-bio]/Neurons and Cognition [q-bio.NC]/Neurobiology; Biophysics; [SDV.NEU.PC] Life Sciences [q-bio]/Neurons and Cognition [q-bio.NC]/Psychology and behavior; Receptors, Nicotinic; Nicotinic; Medicinal and Biomolecular Chemistry; 03 medical and health sciences; Alkaloids; Models; Structural Biology; Information and Computing Sciences; Receptors; Spiro Compounds; Molecular Biology; 0303 health sciences; [SDV.NEU.PC]Life Sciences [q-bio]/Neurons and Cognition [q-bio.NC]/Psychology and behavior; Molecular Structure; Cell Membrane; Neurosciences; [SDV.NEU.NB] Life Sciences [q-bio]/Neurons and Cognition [q-bio.NC]/Neurobiology; Molecular; [SDV.NEU.SC]Life Sciences [q-bio]/Neurons and Cognition [q-bio.NC]/Cognitive Sciences; Biological Sciences; 540; Biological sciences; Kinetics; Chemical sciences; Chemical Sciences; Marine Toxins; Imines; Carrier Proteins; [SDV.NEU.SC] Life Sciences [q-bio]/Neurons and Cognition [q-bio.NC]/Cognitive Sciences; Protein Binding

Pinnatoxins are macrocyclic imine phycotoxins associated with algal blooms and shellfish toxicity. Functional analysis of pinnatoxin A and pinnatoxin G by binding and voltage-clamp electrophysiology on membrane-embedded neuronal α7, α4β2, α3β2, and muscle-type α12βγδ nicotinic acetylcholine receptors (nAChRs) reveals high-affinity binding and potent antagonism for the α7 and α12βγδ subtypes. The toxins also bind to the nAChR surrogate, acetylcholine-binding protein (AChBP), with low Kd values reflecting slow dissociation. Crystal structures of pinnatoxin-AChBP complexes (1.9-2.2 Å resolution) show the multiple anchoring points of the hydrophobic portion, the cyclic imine, and the substituted bis-spiroketal and cyclohexene ring systems of the pinnatoxins that dictate tight binding between the opposing loops C and F at the receptor subunit interface, as observed for the 13-desmethyl-spirolide C and gymnodimine A congeners. Uniquely, however, the bulky bridged EF-ketal ring specific to the pinnatoxins extends radially from the interfacial-binding pocket to interact with the sequence-variable loop F and govern nAChR subtype selectivity and central neurotoxicity.