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Molecular Basis of Good Taste

By Sean Henahan, Access Excellence

San Diego, CA (2/18/99)- Mammals depend on their sense of test for their very survival. Researchers now report the first identification of the genes underlying the molecular basis of taste, a finding with far-reaching implication in many areas of research.

click for larger versionA team of researchers have identified genes that encode two novel proteins expressed in cells specifically geared to the sense of taste. The proteins are members of a new group of "G protein" receptors. They are expressed in taste buds of the tongue and palate.

Graphic: Unlocking the Mysteries of Taste (click for large version).

"The identity of the receptor molecules for the different sensory modalities, like vision, olfaction and taste, represents the Holy Grail of the sensory field. These receptor molecules provide the unique specificity and selectivity of each sensory system. The color receptors in our retinas allow us to see in color and the olfactory receptors in our nose endow us with great olfactory discrimination. In the case of taste, they are what make sweet cells respond to sweet substances, bitter cells to bitter compounds, and so on," notes Charles Zuker, professor of biology and neurosciences at the University of California at San Diego.

Utilizing DNA screening techniques, the researchers scanned for candidate receptors in the taste buds of rats and mice. This led to the isolation of two novel receptors, TR1 and TR2. The molecules belong to a large family of receptors called G protein-coupled receptors. The new proteins are beleivd to be related to the receptors for pheromones, another family of sensory receptors.

Each taste bud contains roughly 50 to 150 taste receptor cells. When they encounter a piece of food, proteins on the surface of these cells bind to the food, recognize them and switch the cells "on" by prompting them into an active state. The cells then transmit information to nerve cells that relay the data to the taste centers of the cortex through synapses in the brain stem and thalamus.

"The identification of candidate mammalian taste receptors makes it possible to understand how the different taste cells differ from each other (for example what makes a sweet cell a sweet cell, etc.) and how taste information is encoded so that the brain can interpret and respond to the presentation of taste stimuli on our tongue. We may be able to mark the different cells and use the marks as a map of the pathway to the brain. Pharmacologically it could be used to identify-using biochemical and biological assays-high potency for agonists and antagonists of taste function."said Zuker.

This research provides the basis for future efforts at manipulating the perception of taste and devising methods to stimulate or block taste cell function. The identification of these genes should also lead to a better understanding of how the sense of taste functions neurologically. The research could also lead to ways to manipulate taste receptors, possibly eliminating bitter and sour tastes from such products as children's medicine.

"These two molecules have the hallmarks we expect of taste receptors. They may be the key to unlocking our understanding of how we detect taste, which is unclear at the moment. We must now demonstrate that functionally they can do the job," said co-investigator Nicholas Ryba of the National Institute of Dental and Craniofacial Research.

The research appears in the February 19, 1999 issue of the scientific journal Cell.

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