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What is a GPCR (G-protein coupled receptor)? Definition & Types

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.

  1. Eicosanoids.
  2. Catecholamine signaling molecules such as Epinephrine, Nor-epinephrine, and Dopamine.
  3. Peptide hormones such as CRH, TRH, TSH, FSH, LH, ACTH, and Vasopressin/ADH.
  4. Neurotransmitters such as Acetylcholine, GABA, Serotonin, and Dopamine.
  5. Neuropeptides.
  6. Interleukins and Chemokines.
  7. 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

  1. Exoplasmic ligand-binding domain.
  2. Transmembrane domain with 7 trans-membrane alpha-helices.
  3. Cytosolic G-protein binding domain.


Key points 

  1. 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.
  2. The third and fourth loops (C-terminal) present in the cytosolic side interact with G-protein.
  3. The binding of the signaling molecules to the GPCR induces a conformational change in the receptor.
  4. The ligand-activated receptors interact with and activate G-protein.