In the past decade a great deal of structural information for class A-GPCRs (G protein-coupled receptors) has emerged. However, the structural and electronic basis of ligand selectivity for closely related receptor subtypes such as the angiotensin receptors AT1aR and AT2R, which present completely diverse biological functions in response to the same ligand, is poorly understood. In order to monitor complex responses in bio systems it is useful to have ligands that present a gradient in terms of selectivity. In this study we present an efficient method to tune ligand selectivity for the two angiotensin II receptor subtypes, AT1aR and AT2R, by controlling aromatic - prolyl interactions in angiotensin II, through alternation of aromatic electronics. On the basis of this strategy, an AT2R selective and high affinity agonist analogue (Ki=3 nM) was obtained.
