title: Phe369(7.38) at human 5-HT(7) receptors confers interspecies selectivity to antagonists and partial agonists.
abstract: OBJECTIVE
  Human and rat 5-HT(7) receptors were studied with a particular emphasis on the molecular interactions involved in ligand binding, searching for an explanation to the interspecies selectivity observed for a set of compounds. We performed affinity studies, molecular modelling and site-directed mutagenesis, with special focus on residue Phe(7.38) of the human 5-HT(7) receptor [Cys(7.38) in rat].
  
  
  METHODS
  Competition binding studies were performed for seven 5-HT(7) receptor ligands at three different 5-HT(7) receptors. The functional behaviour was evaluated by measuring 5-carboxytryptamine-stimulated cAMP production. Computational simulations were carried out to explore the structural bases in ligand binding observed for these compounds.
  
  
  RESULTS
  Competition experiments showed a remarkable selectivity for the human receptor when compared with the rat receptor. These results indicate that mutating Cys to Phe at position 7.38 profoundly affects the binding affinities at the 5-HT(7) receptor. Computational simulations provide a structural interpretation for this key finding. Pharmacological characterization of compounds mr25020, mr25040 and mr25053 revealed a competitive antagonistic behaviour. Compounds mr22423, mr22433, mr23284 and mr25052 behaved as partial agonists.
  
  
  CONCLUSIONS
  We propose that the interspecies difference in binding affinities observed for the compounds at human and rat 5-HT(7) receptors is due to the nature of the residue at position 7.38. Our molecular modelling simulations suggest that Phe(7.38) in the human receptor is integrated in the hydrophobic pocket in the central part of the binding site [Phe(6.51)-Phe(6.52)] and allows a tighter binding of the ligands when compared with the rat receptor.
authors.affiliation: Centre d'Etudes et de Recherche sur le Médicament de Normandie, UFR des Sciences Pharmaceutiques, Université de Caen Basse-Normandie, France.
authors.forename: Thibault
authors.initials: T
authors.lastname: Varin
authors.forename: Hugo
authors.initials: H
authors.lastname: Gutiérrez-de-Terán
authors.forename: Marián
authors.initials: M
authors.lastname: Castro
authors.forename: José
authors.initials: J
authors.lastname: Brea
authors.forename: Frederic
authors.initials: F
authors.lastname: Fabis
authors.forename: François
authors.initials: F
authors.lastname: Dauphin
authors.forename: Johan
authors.initials: J
authors.lastname: Aqvist
authors.forename: Alban
authors.initials: A
authors.lastname: Lepailleur
authors.forename: Pilar
authors.initials: P
authors.lastname: Perez
authors.forename: Javier
authors.initials: J
authors.lastname: Burgueño
authors.forename: José Miguel
authors.initials: JM
authors.lastname: Vela
authors.forename: Maria Isabel
authors.initials: MI
authors.lastname: Loza
authors.forename: Jordi
authors.initials: J
authors.lastname: Rodrigo
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002460:Cell Line; D003198:Computer Simulation; D000242:Cyclic AMP / Q000378:metabolism; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed / Q000379:methods; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D012702:Serotonin Antagonists / Q000494:pharmacology*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D013045:Species Specificity
chemical_list: D008024:Ligands; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; C104425:serotonin 7 receptor; D000242:Cyclic AMP