Preference for sweetness over bitterness is not just a matter of taste. Bitter compounds are often deadly, whereas sweet ones are rich in carbohydrates with high nutritive value. Receptor proteins (or taste receptors) on nerve cells in the taste buds distinguish between them. Bitter compounds bind to the receptors, which triggers an electrical stimulus to the brain and leads to the sensation of taste. Over the past few years, receptors and signaling proteins responsible for bitter taste have been identified but, until now, the identity of the 'sweet' taste receptor has been a mystery.
Robert Margolskee and colleagues (of Mount Sinai School of Medicine, New York, USA) have now identified the first candidate receptor for sweetness (Nature Genetics, Vol. 28, No. 1, 01 May 2001). They used mouse strains that are unable to detect most sugars or sweeteners, such as saccharin. It had previously been established that the gene that determines their ability to taste sweet compounds is located at the end of chromosome 4. The taste receptors identified so far (receptive to bitter tastants and umami) belong to a family of proteins called the G-coupled receptors, so the researchers looked for genes with similar motifs in the chromosome-4 region and found one, T1R3. As might be expected of a taste-receptor gene, its corresponding protein is produced only in a subset of taste-bud neurons. More importantly, all non-taster mice carry a mutation in T1R3 gene that is predicted to impair the function of the receptor. These results indicate that T1R3 is the sweet tooth receptor, although further experiments are necessary to prove the case. This discovery may lead to a new generation of 'designer' sweeteners and a greater understanding of how molecular codes enable taste discrimination.
Dr. Robert Margolskee
Mount Sinai School of Medicine
New York University
New York, New York - USA
Telephone: +1 212-659-8611
Fax: +1 212-849-2599
Dr. Peter Mombaerts
The Rockefeller University
New York, New York - USA
Telephone: +1 212-327-7300
Fax: +1 212-327-7310
(C) Nature Genetics press release.
A related paper, by Linda Buck (of Harvard Medical School, Boston, USA) and colleagues is in May's issue of Nature Neuroscience [See Hum-Molgen posting on Candidate Gene Encoding A Sweet Receptor].
Message posted by: Trevor M. D'Souza
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