The highly conserved DRY motif of class A G protein-coupled receptors: beyond the ground state.
Despite extensive study of heptahelical G protein-coupled receptors (GPCRs), the precise mechanism of G protein activation is unknown. The role of one highly conserved stretch of residues, the amino acids glutamic acid/aspartic acid-arginine-tyrosine (i.e., the E/DRY motif), has received considerable attention with respect to regulating GPCR conformational states. In the consensus view, glutamic acid/aspartic acid maintains the receptor in its ground state, because mutations frequently induce constitutive activity (CA). This hypothesis has been confirmed by the rhodopsin ground-state crystal structure and by computational modeling approaches. However, some class A GPCRs are resistant to CA, suggesting alternative roles for the glutamic acid/aspartic acid residue and the E/DRY motif. Here, we propose two different subgroups of receptors within class A GPCRs that make different use of the E/DRY motif, independent of the G protein type (G(s), G(i), or G(q)) to which the receptor couples. In phenotype 1 receptors, nonconservative mutations of the glutamic acid/aspartic acid-arginine residues, besides inducing CA, increase affinity for agonist binding, retain G protein coupling, and retain an agonist-induced response. In contrast, in second phenotype receptors, the E/DRY motif is more directly involved in governing receptor conformation and G protein coupling/recognition. Hence, mutations of the glutamic acid/aspartic acid residues do not induce CA. Conversely, nonconservative mutations of the arginine of the E/DRY motif always impair agonist-induced receptor responses and, generally, reduce agonist binding affinity. Thus, it is essential to look beyond the rhodopsin ground-state model of conformational activation to clarify the role of this highly conserved triplet in GPCR activation and function.
Rovati
G Enrico
GE
Laboratory of Molecular Pharmacology, Department of Pharmacological Sciences, University of Milan, Via Balzaretti 9, 20133 Milan, Italy. genrico.rovati@unimi.it
Capra
Valérie
V
Neubig
Richard R
RR
D020816:Amino Acid Motifs / Q000502:physiology; D017124:Conserved Sequence / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000378:metabolism; D009154:Mutation; D011487:Protein Conformation; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D043562:Receptors, G-Protein-Coupled; D019204:GTP-Binding Proteins