Site-Directed Mutagenesis of α-Adrenergic Receptors

Abstract

The application of in vitro site-directed mutagenesis has led to the identification of conserved amino acids that play important roles in receptor structure and function. Precise amino acid substitutions can be obtained and then correlated with changes in receptor phenotype. Here, we describe several techniques commonly employed to Introduce site-specific mutations. The benefits and potential drawbacks of each method are discussed. Site-directed mutagenesis of the human α_2A-adrenergic receptor (α_2AAR) has been successfully employed to identify conserved amino acids involved in agonist binding and receptor activation. Aspartate residues in the second and intracellular side of the third transmembrane domain of the α_2AAR are implicated in receptor/G-protein interactions. Since these aspartate residues are highly conserved among all G-protein-coupled receptors, and elimination of these residues has been shown to abolish the ability of other receptors in this class to activate their respective intracellular signaling pathways, It seems likely that these residues are critical for agonist-induced conformational changes that underlie receptor/G-protein interactions. In contrast to the role played by the conserved residues mentioned above, a conserved aspartate residue situated near the extracellular side of the third transmembrane domain plays a pivotal role in adrenergic ligand binding. Genetic analysis of the fifth transmembrane domain of the α_2AAR suggests that a conserved serine residue in this region participates in hydrogen binding to the meta-hydroxyl group of catecholamines. These findings point to the utility of site-directed mutagenesis in identifying structure-function relationships among G-protein-coupled receptors.