Observations collected and published in Nature show a molecular view of the structural changes a taste receptor undergoes when food binds. This bond is then believed to set off a series of mechanisms in the taste cells.
The findings will prove valuable in the development of a new taste evaluation system, which food makers would find invaluable in enhancing the taste of their products, especially when substituting an ‘unhealthy’ ingredient for a healthier but blander-tasting alternative.
Efforts to produce such an evaluation system have been hampered by difficulties in recreating a stable structure and function of a taste receptor in lab conditions. This has resulting in a limited understanding of the processes of taste substance binding.
Study details
Isolating the taste receptors of Medaka fish using insect cells, the team from Osaka University were able to produce a special type of chemical molecule known as a heterodimer.
The heterodimer’s structure contained specialised domains (T1r2 and T1r3) that are responsible for binding of chemical substances eliciting the umami or sweet taste.
Various analytical techniques revealed that the extracellular domain structure of the taste receptor proteins changed into a compact state as food became bound to it.
They also discovered that this structure change was heavily influenced by the protein molecules that make up the heterodimer.
The team suggested that feedback on taste substance binding, which takes place outside of the cell, is transmitted to one third of receptors located in the transmembrane and the intracellular domain.
“The study provided evidence that the ligand binding induces the conformational change of the ligand binding domain (LBD), which has been long assumed but not yet actually demonstrated,” the authors noted.
“Each LBD conformation may correspond to a distinct receptor functional state of T1r, and/or the transition between them might induce the transition between distinct functional states.”
The science of taste
Taste sensation is caused by interactions between taste substances (food) and taste receptors located in the taste buds of the oral cavity.
One of these receptors is the taste receptor type 1, the T1r family, which are found in vertebrates including fishes, birds, and mammals.
The heterodimer of T1r2 and T1r3 recognizes sweet taste substances such as sugars and artificial sweeteners, while the heterodimer of T1r1 and T1r3 identifies umami taste substances such as L-glutamate.
The findings represent a major step forward in realising the accurate analyses of taste mechanisms in humans using purified protein samples produced in the clinical setting.
The researchers believe that if the production of human taste receptors in larger numbers becomes possible, an evaluation system for taste substances may become a reality meaning scientists will be able to measure what humans perceive as palatable.
Source: Nature/Scientific Reports
Published online ahead of print, doi:10.1038/srep25745
“Taste substance binding elicits conformational change of taste receptor T1r heterodimer extracellular domains.”
Authors: Atsuko Yamashita et al.