Taste information derived from T1R-expressing taste cells in mice

Abstract

The taste system of animals is used to detect valuable nutrients and harmful compounds in foods. In humans and mice, sweet, bitter, salty, sour and umami tastes are considered the five basic taste qualities. Sweet and umami tastes are mediated by G-protein-coupled receptors, belonging to the T1R (taste receptor type 1) family. This family consists of three members (T1R1, T1R2 and T1R3). They function as sweet or umami taste receptors by forming heterodimeric complexes, T1R1+T1R3 (umami) or T1R2+T1R3 (sweet). Receptors for each of the basic tastes are thought to be expressed exclusively in taste bud cells. Sweet (T1R2+T1R3-expressing) taste cells were thought to be segregated from umami (T1R1+T1R3-expressing) taste cells in taste buds. However, recent studies have revealed that a significant portion of taste cells in mice expressed all T1R subunits and responded to both sweet and umami compounds. This suggests that sweet and umami taste cells may not be segregated. Mice are able to discriminate between sweet and umami tastes, and both tastes contribute to behavioural preferences for sweet or umami compounds. There is growing evidence that T1R3 is also involved in behavioural avoidance of calcium tastes in mice, which implies that there may be a further population of T1R-expressing taste cells that mediate aversion to calcium taste. Therefore the simple view of detection and segregation of sweet and umami tastes by T1R-expressing taste cells, in mice, is now open to re-examination.

Whole transcriptome profiling of taste bud cells

“…Although initial reports 4, 40 suggested that Tas1r3 is co-expressed with either Tas1r1 or Tas1r2 , or sometimes with no other Tas1r gene, more recent work 41, 42 using RT-PCR of single taste cells reported co-expression of all three Tas1r genes and physiological responses to both sweet and umami tastants. The existence of cells expressing both sweet ( Tas1r2  +  Tas1r3 ) and umami ( Tas1r1  +  Tas1r3 ) receptor genes is inconsistent with strict labelled line models of taste quality coding 43 and raises the possibility of a more distributed mechanism for sweet and umami detection.…”

Sweet Taste Receptors Mediated ROS-NLRP3 Inflammasome Signaling Activation: Implications for Diabetic Nephropathy

“…Among five basic taste qualities, sweet taste permits the identification of energy-rich nutrients, which are very attractive for animals and influence food intake [ 5 , 6 ]. Studies have revealed two classes of GPCRs that have been identified, including taste 1 receptor family (T1R) and the taste 2 receptor family (T2R), and two subtypes of the T1R family, including T1R member 2 (T1R2) and T1R member 3 (T1R3), form heterodimers to act as sweet taste receptors (STRs), which are expressed in taste buds and in the gastrointestinal tract and respond to various chemically distinct compounds, such as natural sugars, noncaloric artificial and natural sweeteners, some D-amino acids, and sweet-tasting proteins [ 7 ]. As a natural ligand for STRs, glucose binding to STRs leads to activation of the heteromeric G α -gustducin.…”

Sweeter and stronger: enhancing sweetness and stability of the single chain monellin MNEI through molecular design

“…This is the same receptor responsible for sensing all classes of sweet compounds, including sugars and small molecular weight sweeteners. Different sweet substances are recognised by different regions of the receptor 16 17 18 19 , but the large dimension of sweet proteins suggests an alternative mode of interaction. The proposed hypothesis to explain this phenomenon is the wedge model 17 20 21 , which suggests that, like other GPCRs, the sweet taste receptor exists in equilibrium between an active and a resting form; sweet proteins might stabilise the active form of the T1R2-T1R3 dimer by binding a wide cleft spanning both subunits of the receptor.…”