Mapping Peptide Antagonist Binding Sites of the Human V1a and V2 Vasopressin Receptors

For many reasons, the arginine vasopressin (AVP)/oxytocin (OT) receptor family is a particularly suitable system to investigate structure-function relationships among G protein-coupled receptors (GPCR): 1) the Vl a, Vlb, V2 vasopressin receptor subtypes and the OT receptor share a high primary sequence homology. 2) they display a great diversity in their pharmacological and functional properties. 3) a lot of peptide and nonpeptide ligands have been developed and characterized. Constructing three-dimensional (3D) models of these receptors and docking the endogenous ligands vasopressin and oxytocin, already allowed us to localize a transmembrane agonist-binding site (1). Moreover, a residue responsible for the receptor binding selectivity has been found in the first extracellular loop (2). However, these first results towards the identification of AVP/OT receptor binding sites led to very few informations to the definition of antagonist binding domains.