Question

What is the relationship between GPCR and G-protein？

Answer 1

GPCR (G-protein coupled receptor) is the largest family of cell surface receptor, mostly found in all eukaryotes. G protein is guanine nucleotide-binding protein. GPCR transmit signals to intracellular targets with the help of G protein. They include the receptors for many neurotransmitters, neuropeptides and peptide hormones. GPCR family includes various number of receptors which is responsible for smell, light and taste.

Although different signal molecules (with chemical and functional diversity) binds to them, all GPCR have similar structure, they all consist of a single polypeptide of multipass nature. It's also called serpentine receptor because this G protein coupled receptor cross the lipid bilayer seven times.

This GPCR are linked to G-proteins. G- proteins are basically GTPase switch proteins. G-proteins are mainly two types : trimeric G-protein and monomeric G-protein. When they are bound to GTP, the protein becomes turned ON and they turned OFF when they are bound with GDP.

In absence of signal, G-protein is bound to GDP, GDP is released when signal activates, subsequent binding of GTP to G-protein is favoured by higher concentration of GTP in the cell. Intrinsic GTPase activity of these GTP-binding proteins hydrolyze the bound GTP to GDP and Pi, active form becomes inactivate again.