MUTATIONAL ANALYSIS OF LIGAND-BINDING ACTIVITY OF BETA-2 ADRENERGIC-RECEPTOR EXPRESSED IN ESCHERICHIA-COLI

A novel in situ screening procedure was used to identify neutral mutations in the human β2 adrenergic receptor (β2AR). The coding region of the human β2AR gene was subcloned under transcriptional control of an inducible T7 promoter and used to transform Escherichia coli. Colonies expressing the β2AR bound the radiolabeled antagonist [125I]iodocyanopindolol and could be identified by autoradiography after transfer to nitrocellulose filters. The region of the β2AR between residues 76 and 83, in the second transmembrane helix, was mutagenized by a saturation mutagenesis technique, so that virtually all of the β2AR genes contained at least one mutation. Colonies retaining ligand binding activity were isolated using the in situ screen. Sequence analysis of the active mutant receptor genes allowed the identification of individual amino acid side chains which are essential for either ligand binding or structural integrity of the β2AR receptor.