Question

How many proteins are there in a G-protein complex that binds to GPCRs?

Answer 1

According to the recent studies on available DNA sequence there are 750 G protein-coupled receptors found in the human genome. Among them about 350 G-protein functions in detection of hormones, growth factors and endogenous ligands and 150 of the GPCRs have unknown functions.

G protein-coupled receptors (GPCRs) are a large protein family of receptors that detect molecules outside the cell and activate internal signal transduction pathways and cellular responses. (Synonyms: heptahelical receptors, serpentine receptor and G protein-linked receptors (GPLR)), Coupling with G proteins, they are called seven-transmembrane receptors (otherwise known as seven-(pass)-transmembrane domain receptors (7TM receptors), because they pass through the cell membrane seven times. G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior.

A conformational change in the GPCR occurs when a ligand binds to the GPCR and it allows toact as a guanine nucleotide exchange factor (GEF). The GPCR is activating with G protein by exchanging the GDP bound to the G protein for a GTP. The G protein's α subunit, together with the bound GTP dissociate from the β and γ subunits and it affetcs intracellular signaling proteins or target functional proteins directly depending on the α-subunit type (G_αs, G_αi/o, G_αq/11, G_α12/13).