Answer to Question #96223 in Biochemistry for Nathaly orozco

Question

Use any specific example from the research literature to explain the mechanism whereby G protein-coupled receptors (GPCRs) and G proteins work together to transmit signals from hormones to regulate metabolism in cells and, therefore, various physiological functions.

Answer 1

The beta-2 adrenergic receptor (β2 adrenoreceptor) is a specific example of G protein-coupled receptors (GPCRs). This receptor is activated by epinephrine (adrenaline) and is localized in different cell types mediating various effects of the short stress hormone. In particular, the β2-adrenergic receptor is localized on the surface of the liver cells. This receptor is a transmembrane protein interacting with epinephrine on the outer side of the membrane and binds effector proteins inside the cell. G_s-proteins consisting of 3 subunits (α, β, and γ) are attached to the inner side of the membrane of the liver cells and interact with the cytoplasmic part of GPCR. Binding of epinephrine to the β2-adrenergic receptor activates its conformational changes causing the dissociation of the G-protein into the α-subunit and β-γ subunit. The α-subunit exchanges the attached GDF to GTP and activates the membrane-associated enzyme adenylate cyclase. Activated adenylate cyclase catalyzes the formation of cAMP (cyclic adenosine monophosphate) from ATP. This molecule is used for signal transmission in many intracellular processes and serves as one of the universal secondary messengers in various cell types. For example, in the liver cells, cAMP activates protein kinase A that phosphorylates phosphorylase kinase. Activated phosphorylase kinase phosphorylates glycogen phosphorylase, stimulating glycogenolysis associated with the release of glucose into the blood flow.