Study of interaction between agonists and Asn293 in helix VI of human beta(2)-adrenergic receptor

Previously, we demonstrated the involvement of Asn293 in helix VI of the hu man beta(2)-adrenergic receptor in stereoselective agonist recognition and activation. In the present study, we have further explored the role of this residue by synthesizing derivatives of isoproterenol and clenbuterol, two beta-adrenergic receptor agonists. We analyzed their efficacy and affinity on the wild-type and a mutant receptor (Asn293Leu). Each compound had simil ar efficacy (tau values) on both the wild-type and mutant receptor, althoug h tau values varied considerably among the eight compounds studied. It appe ared that one derivative of isoproterenol, but not of clenbuterol, showed a gain in affinity from the wild type to the mutant receptor. This derivativ e had a methyl substituent instead of the usual beta-OH group in the alipha tic side chain of isoproterenol, compatible with the more lipophilic nature of the leucine side chain. Such a "gain of function" approach through a co mbination of synthetic chemistry with molecular biology, may be useful to e nhance our insight into the precise atomic events that govern ligand-recept or interactions.