G protein coupled receptor [Homo sapiens] (Synonyms: H2N-Gln-Glu-Ser-His-Asn-Ser-Gly-Asn-Arg-Ser-Asp-Gly-Pro-Gly-Lys-Asn-Thr-Thr-Leu-His-Asn-Glu-Phe-Asp-Thr-OH )

G protein coupled receptors (GPCRs), also known as seven-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptor, and G protein-linked receptors (GPLR), constitute a large protein family of receptors that sense molecules outside the cell and activate inside signal transduction pathways and, ultimately, cellular responses. They are called transmembrane receptors because they pass through the cell membrane, and they are called seven-transmembrane receptors because they pass through the cell membrane seven times⁽¹⁾.GPCRs are involved in a wide variety of physiological processes. The visual sense: the opsins use a photoisomerization reaction to translate electromagnetic radiation into cellular signals. Rhodopsin, for example, uses the conversion of 11-cis-retinal to all-trans-retinal for this purpose The sense of smell: receptors of the olfactory epithelium bind odorants (olfactory receptors) and pheromones (vomeronasal receptors) Behavioral and mood regulation: receptors in the mammalian brain bind several different neurotransmitters, including serotonin, dopamine, GABA, and glutamate Regulation of immune system activity and inflammation: chemokine receptors bind ligands that mediate intercellular communication between cells of the immune system; receptors such as histamine receptors bind inflammatory mediators and engage target cell types in the inflammatory response Autonomic nervous system transmission: both the sympathetic and parasympathetic nervous systems are regulated by GPCR pathways, responsible for control of many automatic functions of the body such as blood pressure, heart rate, and digestive processes Cell density sensing: A novel GPCR role in regulating cell density sensing. Homeostasis modulation ⁽²⁾.Involved in growth and metastasis of some types of tumors⁽³⁾.

Figure1  the structures of G protein coupled receptor

Figure 2  Diversity of G-protein-coupled receptor signalling.

Ref:

1. Wu H, Wacker D, Mileni M, Katritch V, Han GW, Vardy E, Liu W, Thompson AA, Huang XP, Carroll FI, Mascarella SW, Westkaemper RB, Mosier PD, Roth BL, Cherezov V, Stevens RC (May 2012). "Structure of the human κ-opioid receptor in complex with JDTic". Nature 485 (7398): 327–32.

2. Hazell GG, Hindmarch CC, Pope GR, Roper JA, Lightman SL, Murphy D, O'Carroll AM, Lolait SJ (July 2011). "G protein-coupled receptors in the hypothalamic paraventricular and supraoptic nuclei - serpentine gateways to neuroendocrine homeostasis". Front Neuroendocrinol 33 (1): 45–66.

3. Dorsam RT, Gutkind JS. (Feb 2007). "G-protein-coupled receptors and cancer". Nat Rev Cancer 7 (2): 79–94.