Phe369(7.38) at human 5-HT(7) receptors confers interspecies selectivity to antagonists and partial agonists.
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.
Varin
Thibault
T
Centre d'Etudes et de Recherche sur le Médicament de Normandie, UFR des Sciences Pharmaceutiques, Université de Caen Basse-Normandie, France.
Gutiérrez-de-Terán
Hugo
H
Castro
Marián
M
Brea
José
J
Fabis
Frederic
F
Dauphin
François
F
Aqvist
Johan
J
Lepailleur
Alban
A
Perez
Pilar
P
Burgueño
Javier
J
Vela
José Miguel
JM
Loza
Maria Isabel
MI
Rodrigo
Jordi
J
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
D008024:Ligands; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; C104425:serotonin 7 receptor; D000242:Cyclic AMP