title: Identification and functional expression of a glutamate- and avermectin-gated chloride channel from Caligus rogercresseyi, a southern Hemisphere sea louse affecting farmed fish.
abstract: Parasitic sea lice represent a major sanitary threat to marine salmonid aquaculture, an industry accounting for 7% of world fish production. Caligus rogercresseyi is the principal sea louse species infesting farmed salmon and trout in the southern hemisphere. Most effective control of Caligus has been obtained with macrocyclic lactones (MLs) ivermectin and emamectin. These drugs target glutamate-gated chloride channels (GluCl) and act as irreversible non-competitive agonists causing neuronal inhibition, paralysis and death of the parasite. Here we report the cloning of a full-length CrGluClα receptor from Caligus rogercresseyi. Expression in Xenopus oocytes and electrophysiological assays show that CrGluClα is activated by glutamate and mediates chloride currents blocked by the ligand-gated anion channel inhibitor picrotoxin. Both ivermectin and emamectin activate CrGluClα in the absence of glutamate. The effects are irreversible and occur with an EC(50) value of around 200 nM, being cooperative (n(H) = 2) for ivermectin but not for emamectin. Using the three-dimensional structure of a GluClα from Caenorabditis elegans, the only available for any eukaryotic ligand-gated anion channel, we have constructed a homology model for CrGluClα. Docking and molecular dynamics calculations reveal the way in which ivermectin and emamectin interact with CrGluClα. Both drugs intercalate between transmembrane domains M1 and M3 of neighbouring subunits of a pentameric structure. The structure displays three H-bonds involved in this interaction, but despite similarity in structure only of two these are conserved from the C. elegans crystal binding site. Our data strongly suggest that CrGluClα is an important target for avermectins used in the treatment of sea louse infestation in farmed salmonids and open the way for ascertaining a possible mechanism of increasing resistance to MLs in aquaculture industry. Molecular modeling could help in the design of new, more efficient drugs whilst functional expression of the receptor allows a first stage of testing of their efficacy.
authors.affiliation: Centro de Estudios Científicos (CECs), Valdivia, Chile.
authors.forename: Isabel
authors.initials: I
authors.lastname: Cornejo
authors.affiliation: UPMC Université Paris 06, UMR_S 1138, Team 3, Paris, France; INSERM, UMR_S 872, Paris, France.
authors.forename: Olga
authors.initials: O
authors.lastname: Andrini
authors.affiliation: Centro de Estudios Científicos (CECs), Valdivia, Chile.
authors.forename: María Isabel
authors.initials: MI
authors.lastname: Niemeyer
authors.affiliation: Universidad Andrés Bello, Centro de Bioinformática y Biología Integrativa, Facultad de Ciencias Biológicas, Santiago, Chile.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Marabolí
authors.affiliation: Universidad Andrés Bello, Centro de Bioinformática y Biología Integrativa, Facultad de Ciencias Biológicas, Santiago, Chile.
authors.forename: F Danilo
authors.initials: FD
authors.lastname: González-Nilo
authors.affiliation: UPMC Université Paris 06, UMR_S 1138, Team 3, Paris, France; INSERM, UMR_S 872, Paris, France.
authors.forename: Jacques
authors.initials: J
authors.lastname: Teulon
authors.affiliation: Centro de Estudios Científicos (CECs), Valdivia, Chile.
authors.forename: Francisco V
authors.initials: FV
authors.lastname: Sepúlveda
authors.affiliation: Centro de Estudios Científicos (CECs), Valdivia, Chile.
authors.forename: L Pablo
authors.initials: LP
authors.lastname: Cid
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D018118:Chloride Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D033342:Copepoda / Q000187:drug effects / Q000502:physiology*; D004594:Electrophysiology; D005260:Female; D005393:Fish Diseases / Q000235:genetics / Q000378:metabolism* / Q000469:parasitology; D005399:Fishes / Q000254:growth & development / Q000378:metabolism / Q000469:parasitology*; D018698:Glutamic Acid / Q000494:pharmacology*; D007306:Insecticides / Q000494:pharmacology; D007559:Ivermectin / Q000031:analogs & derivatives* / Q000494:pharmacology; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D008969:Molecular Sequence Data; D009865:Oocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014982:Xenopus laevis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
chemical_list: D018118:Chloride Channels; D007306:Insecticides; C109777:glutamate-gated chloride channels; D018698:Glutamic Acid; D007559:Ivermectin; C019264:avermectin