Phosphorylation of G Protein-Coupled Receptors: From the Barcode Hypothesis to the Flute Model

Abstract

Seven transmembrane G protein-coupled receptors (GPCRs) are often phosphorylated at the C terminus and on intracellular loops in response to various extracellular stimuli. Phosphorylation of GPCRs by GPCR kinases and certain other kinases can promote the recruitment of arrestin molecules. The arrestins critically regulate GPCR functions not only by mediating receptor desensitization and internalization, but also by redirecting signaling to G protein-independent pathways via interactions with numerous downstream effector molecules. Accumulating evidence over the past decade has given rise to the phospho-barcode hypothesis, which states that ligand-specific phosphorylation patterns of a receptor direct its distinct functional outcomes. Our recent work using unnatural amino acid incorporation and fluorine-19 nuclear magnetic resonance (F-NMR) spectroscopy led to the flute model, which provides preliminary insight into the receptor phospho-coding mechanism, by which receptor phosphorylation patterns are recognized by an array of phosphate-binding pockets on arrestin and are translated into distinct conformations. These selective conformations are recognized by various effector molecules downstream of arrestin. The phospho-barcoding mechanism enables arrestin to recognize a wide range of phosphorylation patterns of GPCRs, contributing to their diverse functions.

Identification of Phosphorylation Codes for Arrestin Recruitment by G Protein-Coupled Receptors

“…Of the 389 receptors without codes in their tails, 308 (~79%) were found to belong to the olfactory receptor family, which has been shown to recruit arrestin through phosphorylation sites within their ICL3 just N-terminal to TM6 (Mashukova et al, 2006). Analysis of the remaining 81 receptors found that 48 contained full or partial codes within their ICL3 and comprised many members from the serotonin, dopamine, muscarinic, and α-adrenergic families, which have been shown to recruit β-arrestins in a ICL3-dependent manner (Smith and Rajagopal, 2016; Yang et al, 2017). In total, our phosphorylation code analysis accounts for 96% of the GPCR proteome.…”

Stepwise phosphorylation of leukotriene B 4 receptor 1 defines cellular responses to leukotriene B 4

“…It has been demonstrated that the distinct GPCR phosphorylation profiles that result from the actions of different kinases are responsible for various signaling outcomes. This concept is known as the "phosphorylation barcode" and is critical for the multidimensional features of GPCR signaling (3)(4)(5)(6)(43)(44)(45). Thus, the precise analysis of BLT1 phosphorylation is important to clarify the biological functions of this receptor.…”

Receptor‐Like Kinase Phosphorylation of Arabidopsis Heterotrimeric G‐Protein Gα ‐Subunit AtGPA1

“…Phosphorylation of seven transmembrane (7TM) GPCRs is a regulatory mechanism to modulate G protein signaling . In animals, extracellular signals induce GPCR phosphorylation by G protein–coupled receptor kinases (GRKs) on the C‐terminus and intracellular loops leading to arrestin recruitment and signal desensitization through receptor endocytosis.…”

“…In animals, extracellular signals induce GPCR phosphorylation by G protein–coupled receptor kinases (GRKs) on the C‐terminus and intracellular loops leading to arrestin recruitment and signal desensitization through receptor endocytosis. Phosphorylation patterns of GPCR are recognized by arrestins via a phospho‐barcoding mechanism to activate arrestin‐dependent effectors in diverse cellular processes . In Arabidopsis thaliana , AtGPA1 is kept in its deactivated state by a 7TM GAP (AtRGS1) and the ligand‐induced phosphorylation and endocytosis of AtRGS1 activates AtGPA1 via de‐repression …”