RESUMEN
G protein-coupled receptor kinases (GRKs) phosphorylate agonist-occupied receptors initiating the processes of desensitization and ß-arrestin-dependent signaling. Interaction of GRKs with activated receptors serves to stimulate their kinase activity. The extreme N-terminal helix (αN), the kinase small lobe, and the active site tether (AST) of the AGC kinase domain have previously been implicated in mediating the allosteric activation. Expanded mutagenesis of the αN and AST allowed us to further assess the role of these two regions in kinase activation and receptor phosphorylation in vitro and in intact cells. We also developed a bioluminescence resonance energy transfer-based assay to monitor the recruitment of GRK2 to activated α(2A)-adrenergic receptors (α(2A)ARs) in living cells. The bioluminescence resonance energy transfer signal exhibited a biphasic response to norepinephrine concentration, suggesting that GRK2 is recruited to Gßγ and α(2A)AR with EC50 values of 15 nM and 8 µM, respectively. We show that mutations in αN (L4A, V7E, L8E, V11A, S12A, Y13A, and M17A) and AST (G475I, V477D, and I485A) regions impair or potentiate receptor phosphorylation and/or recruitment. We suggest that a surface of GRK2, including Leu(4), Val(7), Leu(8), Val(11), and Ser(12), directly interacts with receptors, whereas residues such as Asp(10), Tyr(13), Ala(16), Met(17), Gly(475), Val(477), and Ile(485) are more important for kinase domain closure and activation. Taken together with data on GRK1 and GRK6, our data suggest that all three GRK subfamilies make conserved interactions with G protein-coupled receptors, but there may be unique interactions that influence selectivity.
Asunto(s)
Quinasa 2 del Receptor Acoplado a Proteína-G/química , Simulación del Acoplamiento Molecular/métodos , Mapeo de Interacción de Proteínas/métodos , Receptores Acoplados a Proteínas G/química , Secuencia de Aminoácidos , Animales , Sitios de Unión/genética , Células COS , Dominio Catalítico , Chlorocebus aethiops , Quinasa 2 del Receptor Acoplado a Proteína-G/genética , Quinasa 2 del Receptor Acoplado a Proteína-G/metabolismo , Células HEK293 , Humanos , Cinética , Datos de Secuencia Molecular , Mutación , Fosforilación , Unión Proteica , Estructura Terciaria de Proteína , Receptores Adrenérgicos alfa 2/química , Receptores Adrenérgicos alfa 2/genética , Receptores Adrenérgicos alfa 2/metabolismo , Receptores Acoplados a Proteínas G/genética , Receptores Acoplados a Proteínas G/metabolismoRESUMEN
G-protein-coupled receptor (GPCR) kinases (GRKs) were first identified based on their ability to specifically phosphorylate activated GPCRs. Although many soluble substrates have since been identified, the chief physiological role of GRKs still remains the uncoupling of GPCRs from heterotrimeric G-proteins by promoting ß-arrestin binding through the phosphorylation of the receptor. It is expected that GRKs recognize activated GPCRs through a docking site that not only recognizes the active conformation of the transmembrane domain of the receptor but also stabilizes a more catalytically competent state of the kinase domain. Many of the recent gains in understanding GRK-receptor interactions have been gleaned through biochemical and structural analysis of recombinantly expressed GRKs. Described herein are current techniques and procedures being used to express, purify, and assay GRKs in both in vitro and living cells.
