<P> Some web - servers and bioinformatics prediction methods have been used for predicting the classification of GPCRs according to their amino acid sequence alone, by means of the pseudo amino acid composition approach . </P> <P> GPCRs are involved in a wide variety of physiological processes . Some examples of their physiological roles include: </P> <Ol> <Li> The visual sense: The opsins, gradually evolved from early GPCRs over 650 million years ago, 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 . </Li> <Li> The gustatory sense (taste): GPCRs in taste cells mediate release of gustducin in response to bitter - and sweet - tasting substances . </Li> <Li> The sense of smell: Receptors of the olfactory epithelium bind odorants (olfactory receptors) and pheromones (vomeronasal receptors) </Li> <Li> Behavioral and mood regulation: Receptors in the mammalian brain bind several different neurotransmitters, including serotonin, dopamine, GABA, and glutamate </Li> <Li> 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 . GPCRs are also involved in immune - modulation and directly involved in suppression of TLR - induced immune responses from T cells . </Li> <Li> 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 </Li> <Li> Cell density sensing: A novel GPCR role in regulating cell density sensing . </Li> <Li> Homeostasis modulation (e.g., water balance). </Li> <Li> Involved in growth and metastasis of some types of tumors . </Li> <Li> Used in the endocrine system for peptide and amino - acid derivative hormones that bind to GCPRs on the cell membrane of a target cell . This activates cAMP, which in turn activates several kinases, allowing for a cellular response, such as transcription . </Li> </Ol> <Li> The visual sense: The opsins, gradually evolved from early GPCRs over 650 million years ago, 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 . </Li>

Where is the g protein linked receptor located