Definition: GPCR (G-protein coupled receptor) is a well-studied trans-membrane receptor, that can interact with a G-protein towards the cytosolic side, hence the name G-protein coupled receptor.
In general, GPCR receives various signals from other cells and activates internal signaling pathways, ultimately that leads to cellular response. These GPCR receptors are also known as G protein-linked receptors (GPLR), seven transmembrane domain receptors, 7TM receptors, serpentine receptors, and heptahelical receptors.
This receptor passes the cell membrane by seven times and forms the N-terminus outside of the cell membrane (exoplasmic side) and C- terminus inside of the cell (cytosolic side). N-terminus is a site for ligand binding, while C-terminus is a site for G-protein binding.
The signaling molecules of GPCR class include.
- Catecholamine signaling molecules such as Epinephrine, Nor-epinephrine, and Dopamine.
- Peptide hormones such as CRH, TRH, TSH, FSH, LH, ACTH, and Vasopressin/ADH.
- Neurotransmitters such as Acetylcholine, GABA, Serotonin, and Dopamine.
- Interleukins and Chemokines.
- Nucleosides and Nucleotides.
Types of GPCR (It mainly involved in three senses)
- Vision:- here we call GPCR as a photoreceptor
- Taste:- here we call it as Gustatory receptor
- Smell:- here we call it as Olfactory receptor/Odorant receptor
Structurally GPCR comprises
- Exoplasmic ligand-binding domain.
- Transmembrane domain with 7 trans-membrane alpha-helices.
- Cytosolic G-protein binding domain.
- The presence of 7 transmembrane alpha-helices is a distinct character or hallmark of GPCR. Hence the GPCR is called heptahelical receptors, 7 TM receptor, or Serpentine receptor.
- The third and fourth loops (C-terminal) present in the cytosolic side interact with G-protein.
- The binding of the signaling molecules to the GPCR induces a conformational change in the receptor.
- The ligand-activated receptors interact with and activate G-protein.