GPCR/G-protein

G protein-coupled receptors (GPCRs) are also known as seven-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR). They constitute a large protein family of druggable receptors including 5-HT receptors，adrenoceptors，GABA receptors，Histamine receptors，mGluR and angiotensin receptors. GPCRs are only found in eukaryotes and work together with G proteins (also known as guanosine nucleotide-binding proteins) to transmit signals into the cell interior from many hormones, neurotransmitters and other signaling factors outside the cell. This process involves activation of different signal transduction pathways and, ultimately, leads to cellular responses.^[1][2] GPCR signaling principally activates intracellular signaling pathways, including the following pathways: cAMP/PKA, Ca²⁺/PKC, Ca²⁺/NFAT, PLC, PTK, PKC/MEK, Erk1/2 MAPK, p38 MAPK, PI3K, NO-cGMP, Rho, NF-κB and JAK/STAT.^[3] GPCRs control key physiological functions, including neurotransmission, immune responses, cardiac- and smooth-muscle contraction and blood pressure regulation, as well as, hormone and enzyme release from endocrine and exocrine glands. Therefore, the malfunction of GPCRs contributes to some of the most prevalent human diseases. For example, activating mutations of the thyroid stimulating hormone receptor (TSHR) is found in some thyroid carcinomas and approximately 80% of thyroid adenomas, and germline mutations in TSHR cause familial non-autoimmune hyperthyroidism.^[4] Due to GPCRs’ specific role in human disease, they have served as useful targets for drug development. For example, the antipsychotic agents risperidone and escitalopram oxalate block specific GPCRs that normally bind to dopamine or serotonin. A variety of GPCR agonists also exist, such as the drug UCB P071, which is a selective Histamine 1 receptor inverse agonist used in the treatment of allergies, hay fever, angioedema, and urticaria.

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