Lecture 3-13: G protein-coupled receptors

G Protein-Coupled Receptors (GPCRs)

Membrane proteins that span the cell membrane seven times and are involved in signaling by binding to ligands.

Ligand Binding

The process by which a molecule (ligand) binds to a receptor, activating a biological response.

Trimeric G Protein

A protein complex consisting of three subunits (alpha, beta, gamma) that is activated by GPCRs upon ligand binding.

GTPase Activity

The ability of a protein (like the alpha subunit of G proteins) to hydrolyze GTP to GDP, thus inactivating itself.

Regulator of G-Protein Signaling (RGS)

Proteins that accelerate GTP hydrolysis, thereby turning off G protein signaling.

Second Messengers

Intracellular signaling molecules (e.g., cAMP, IP3, DAG) that mediate and amplify signals following receptor activation.

Adenylyl Cyclase

An enzyme that converts ATP to cyclic AMP (cAMP) in response to G protein signaling.

Phospholipase C (PLC)

An enzyme that hydrolyzes PIP2 to yield IP3 and DAG, both of which are involved in cellular signaling.

Calmodulin

A calcium-binding protein that regulates a variety of cellular processes by altering the function of target proteins upon calcium binding.

Photoreceptors

Sensory cells in the retina that detect light, primarily through GPCRs like rhodopsin.

Gq protein

A type of G protein that activates phospholipase C and is involved in signaling pathways that increase intracellular calcium.

CaMK (Calmodulin-dependent protein kinase)

An enzyme that is activated by calmodulin and phosphorylates protein targets in response to calcium levels.

cAMP (Cyclic AMP)

A second messenger molecule derived from ATP that plays a crucial role in transmitting signals from GPCRs.

GDI (Guanine Nucleotide Dissociation Inhibitor)

Proteins that inhibit the release of GDP from G protein subunits, maintaining the inactive state.

Epinephrine

A hormone that activates GPCRs leading to various physiological responses, including increased heart rate.

Nitric Oxide Synthase (NOS)

An enzyme activated by increased calcium levels that catalyzes the production of nitric oxide from L-arginine.

Sildenafil

A drug that inhibits phosphodiesterase, prolonging the effect of cGMP and causing relaxation of smooth muscle.

Calcium Channels

Membrane proteins that allow calcium ions to enter cells, influencing numerous cellular functions.

Glycogen Phosphorylase

An enzyme that breaks down glycogen into glucose-1-phosphate and is activated by phosphorylation through PKA.

Transducin (GaT)

The specific alpha subunit of the G protein associated with rhodopsin, involved in phototransduction.

PKA (Protein Kinase A)

An enzyme that is activated by cAMP and phosphorylates various substrates to mediate cellular responses.

Glucagon

A hormone that stimulates glycogen breakdown in the liver, which is mediated by cAMP signaling.

Gai protein

A type of G protein that inhibits adenylyl cyclase when activated, thus decreasing cAMP levels.

Gaq protein

A type of G protein that activates phospholipase C, leading to increased calcium levels and activation of PKC.