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A protein that leaves a bitter taste in your mouth

More than twenty proteins detect bitter flavors on the human tongue, including substances that may be toxic or may protect against disease. Scientists have now described in detail one of those proteins—a taste receptor—and identified the chemical structures to which it responds.

Surface of cells transfected with TAS2R16. Receptors at the cell surface in yellow (far right). View full

Bitter is nobody's favorite flavor, and for good reason. Spoiled or toxic foods are often bitter, and our perception of bitterness may have evolved to warn humans against eating harmful cuisine.

Yet some bitter flavors—in foods like sprouts and mustard greens—contain nutrients that lower the risk of cancer and heart disease. Some researchers would like to find ways to mask the harsh flavor so people would be more likely to eat these unappealing but healthful foods.

In this study, the researchers analyzed 24 genes mined from the human genome sequence that encode for bitter receptors. They focused on one protein called TAS2R16. The protein detects, for example, an extract from the willow tree that has been used to treat pain and fever for thousands of years.

"TAS2R16 links the recognition of a specific chemical structure to the perception of bitter taste," the researchers write in Nature Genetics. Wolfgang Meyerhof, of the German Institute of Human Nutrition, led the research.

Using protein receptors, the researchers are investigating the biology of taste. "We want to know: Why do we eat what we eat?" says Meyerhof. "And how does taste influence what we eat?"

Humans can detect five tastes: salty, sour, sweet, bitter and umami (amino acids). It is unclear how many protein receptors there are. These proteins reside in taste receptor cells; hundreds of receptor cells make up a taste bud, and thousands of these taste buds cover the human tongue.

"Receptors are tools to understand taste," says Nicholas Ryba, of the National Institutes of Health, who has collaborated with Charles Zuker at the University of California, San Diego to characterize the families of bitter, sweet, and umami receptors.

"Now that researchers have defined receptors, they can get more details about how our sense of taste works," Ryba says. "We want to understand the logic of taste."

See related GNN article
»Sweet-tooth gene discovered

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Bufe, B. et al. The human TAS2R16 receptor mediates bitter taste in response to B-glucopyranosides. Nat Genet. Published online October 15, 2002.

Nelson, G. et al. An amino-acid taste receptor. Nature 416, 199-202 (March 14, 2002).

Nelson, G. et al. Mammalian sweet taste receptors. Cell 106, 381-390 (August 10, 2001).

Adler, E. et al. A novel family of mammalian taste receptors. Cell 100, 693-702 (March 17, 2000).

Chandrashekar, J. et al. T2Rs function as bitter taste receptors. Cell 100, 703-711 (March 17, 2000).

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