Taste receptors in the gastrointestinal system

Abstract

In the last 15 years, advancements in molecular biology have unraveled the proteins that function as taste receptors. There are at least five taste qualities that are consciously perceived, sweet, sour, salty, bitter, and umami. Of these five, sour and salty are mediated by ion channels, whereas the perception of sweet, umami, and bitter tastes is mediated by G protein-coupled receptors (GPCRs). These taste GPCRs belong to the TAS1R and TAS2R gene families. There are other nutrient-binding GPCRs whose taste function is still being studied such as CaSR, GPRC6A, GPR92, or GPR120. It has been suspected for more than a century that the gut can sense the chemical composition of foods. The description of multiple taste GPCRs in gastrointestinal (GI) cells suggests that there are nutrient-sensing mechanisms in the GI tract, oral, gastric, and intestinal mucosa. Oral sensing seems to mainly influence food discrimination and nutrient appetite, while post-oral chemosensors may relate to nutrient utilization and inhibition of appetite. The most common accepted view is that taste GPCRs are present in enteroendocrine cells among others also known as chemosensory cells. These cells express taste receptors and other taste-related genes. Although, functional cells of the GI mucosa that are not enteroendocrine or brush cells such as enterocytes or gastric cells may also hold receptive mechanisms that transduce the presence of certain nutrients in ingested foods and regulate gastric functions. This paper examines the importance of food chemical signals in their association with the neuroendocrine mechanisms they trigger, which are the core for metabolism and appetite regulation.

Tryptophan Biochemistry: Structural, Nutritional, Metabolic, and Medical Aspects in Humans

“…An interesting aspect needing to be deepened, linked to the topic of this review, is that AAAs and, in particular, L-Trp and L-Phe recognize and activate a class of Ca 2+ “sensor” and taste metabotropic receptors whose physiological role is under investigation [ 43 ]. Beside their primary action on Ca 2+ regulation, the high expression of these receptors in the gut implies a main action on feeding, food choice, nutrient absorption, and gastrointestinal function [ 44 – 47 ]. It can be supposed that the extensive study of their localization, gene expression, and function within the body would provide useful information and clinical application.…”

Sugars, Sweet Taste Receptors, and Brain Responses

“…These regions are involved with ingestive motivation, physiological reflexes, and energy homeostasis. Reproduced with permission from [ 50 ].…”

Modeling and simulation in medical sciences: an overview of specific applications based on research experience in EMRI (Endocrinology and Metabolism Research Institute of Tehran University of Medical Sciences)

“…In another context, sweet taste receptor (STR), a class C G-protein coupled receptor (C GPCR), has been suggested as a drug target for designing either new low-calorie sweeteners or drugs to control metabolic condition disorders such as type II diabetes mellitus [ 52 , 53 ]. In order to design appropriate ligands for this receptor, a three-dimensional structure is needed, but since the human receptor structure is still not experimentally elucidated, in silico (molecular modeling) methods were used in this case.…”