G-protein-coupled receptor kinase 3 (GRK3) is an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

that in humans is encoded by the ''ADRBK2''

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

. GRK3 was initially called Beta-adrenergic receptor kinase 2 (βARK-2), and is a member of the

G protein-coupled receptor kinase G protein-coupled receptor kinases (GPCRKs, GRKs) are a family of protein kinases within the AGC (protein kinase A, protein kinase G, protein kinase C) group of kinases. Like all AGC kinases, GRKs use ATP to add phosphate to Serine and Threonine ...

subfamily of the Ser/Thr

protein kinase A protein kinase is a kinase which selectively modifies other proteins by covalently adding phosphates to them (phosphorylation) as opposed to kinases which modify lipids, carbohydrates, or other molecules. Phosphorylation usually results in a fu ...

s that is most highly similar to

GRK2 G-protein-coupled receptor kinase 2 (GRK2) is an enzyme that in humans is encoded by the ''ADRBK1'' gene. GRK2 was initially called Beta-adrenergic receptor kinase (βARK or βARK1), and is a member of the G protein-coupled receptor kinase subfa ...

Function

G protein-coupled receptor kinases phosphorylate activated G protein-coupled receptors, which promotes the binding of an

arrestin Arrestins (abbreviated Arr) are a small family of proteins important for regulating signal transduction at G protein-coupled receptors. Arrestins were first discovered as a part of a conserved two-step mechanism for regulating the activity of ...

protein to the receptor. Arrestin binding to phosphorylated, active receptor prevents receptor stimulation of

heterotrimeric G protein Heterotrimeric G protein, also sometimes referred to as the ''"large" G proteins'' (as opposed to the subclass of smaller, monomeric small GTPases) are membrane-associated G proteins that form a heterotrimeric complex. The biggest non-structu ...

transducer proteins, blocking their cellular signaling and resulting in receptor desensitization. Arrestin binding also directs receptors to specific cellular internalization pathways, removing the receptors from the cell surface and also preventing additional activation. Arrestin binding to phosphorylated, active receptor also enables receptor signaling through arrestin partner proteins. Thus the GRK/arrestin system serves as a complex signaling switch for G protein-coupled receptors. GRK3 and the closely related GRK2 phosphorylate receptors at sites that encourage arrestin-mediated receptor desensitization, internalization and trafficking rather than arrestin-mediated signaling (in contrast to

GRK5 G protein-coupled receptor kinase 5 is a member of the G protein-coupled receptor kinase subfamily of the Ser/Thr protein kinases, and is most highly similar to GRK4 and GRK6. The protein phosphorylates the activated forms of G protein-coupled r ...

and

GRK6 This gene encodes a member of the G protein-coupled receptor kinase subfamily of the Ser/Thr protein kinase family, and is most highly similar to GRK4 and GRK5. The protein phosphorylates the activated forms of G protein-coupled receptors to re ...

, which have the opposite effect). This difference is one basis for pharmacological

biased agonism Functional selectivity (or “agonist trafficking”, “biased agonism”, “biased signaling”, "ligand bias" and “differential engagement”) is the ligand-dependent selectivity for certain signal transduction pathways relative to a referen ...

(also called

functional selectivity Functional selectivity (or “agonist trafficking”, “biased agonism”, “biased signaling”, "ligand bias" and “differential engagement”) is the ligand-dependent selectivity for certain signal transduction pathways relative to a referen ...

), where a drug binding to a receptor may bias that receptor’s signaling toward a particular subset of the actions stimulated by that receptor. GRK3 is expressed broadly in tissues, but generally at lower levels than the related GRK2. GRK3 has particularly high expression in olfactory neurons, and mice lacking the ADRBK2 gene exhibit defects in

olfaction The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, ...

Gene linkage Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction. Two genetic markers that are physically near to each other are unlikely to be s ...

techniques were used to identify a polymorphism in the promoter of the human ADRBK2 gene as a possible cause of up to 10% of cases of

bipolar disorder Bipolar disorder, previously known as manic depression, is a mental disorder characterized by periods of Depression (mood), depression and periods of abnormally elevated Mood (psychology), mood that last from days to weeks each. If the elevat ...

. However, the significance of GRK3 in bipolar disorder has been controversial due to conflicting reports. GRK3 has also been implicated in regulation of

dopamine receptor Dopamine receptors are a class of G protein-coupled receptors that are prominent in the vertebrate central nervous system (CNS). Dopamine receptors activate different effectors through not only G-protein coupling, but also signaling through diffe ...

s in

Parkinson disease Parkinson may refer to: * Parkinson (surname) * ''Parkinson'' (TV series), British chat show, presented by Sir Michael Parkinson * Parkinson, Queensland, suburb of Brisbane, Australia *The Parkinsons (fl. early 20th century), American father-and-so ...

in animal models. Reduced expression of GRK3 has been associated with the

immunodeficient Immunodeficiency, also known as immunocompromisation, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that a ...

WHIM syndrome in humans, and appears causative in a mouse model of the disease.

References

External links

Online version of the paper in ''Molecular Psychiatry''

PubMed abstract

* {{Portal bar, Biology, border=no Biology of bipolar disorder EC 2.7.11

Function

References

Further reading

External links