How sweet it is
Our appreciation of sweet foods begins with an interaction between sugars and specific receptors on taste cells of the tongue. However, despite progress in identifying receptors for other tastes (sour, bitter, salty and umami or glutamate), the sweet taste receptor in mammals has remained elusive. Now, a group led by Linda Buck at Harvard University has identified a candidate gene that may encode a sweet receptor (Nature Neuroscience, Vol. 4, No. 5, 01 May 2001). The group studied two strains of mice: so-called 'tasters', which prefer water containing sugar or saccharin, and 'nontasters', which show far less preference for sweet water.
Based on previous evidence that the sweet taste receptor gene might resemble the bitter and umami receptors (which are G-protein-coupled receptors), the researchers searched for G-protein-coupled receptor genes within the region of the mouse genome known to control the 'taster' or 'nontaster' phenotype.
They found several such genes, but one in particular (T1R3) was expressed in taste cells. Furthermore, they found specific changes in T1R3 (and not the other genes) in the 'nontaster' mice, thus providing further evidence that this gene may function as a sweet taste receptor. Despite the strong circumstantial evidence that T1R3 encodes a sweet taste receptor, definitive proof awaits a functional test. For example, it should be possible to insert T1R3 into a cell that normally does not respond to sweet stimuli. If T1R3 indeed codes for a sweet taste receptor, such a cell should become responsive to sweet stimuli. Experiments of this sort have proven particularly difficult in the taste receptor field. Nevertheless, the work will certainly spark more research in this area, as there is substantial commercial interest in designing new sweeteners. At a more basic level, the work should also help to answer long-standing mysteries such as how responses at single neurons give rise to the complex perception of taste.
Dr. Linda Buck
Department of Neurobiology
Harvard Medical School
220 Longwood Ave.
Boston, Massachusetts 02115
tel: +1 617 432 4803
fax: +1 617 734 7557
(C) Nature Neuroscience press release.
See also similar work from Robert Margolskee and colleagues (Columbia University) in the May issue of Nature Genetics [See Hum-Molgen Posting on Sweet Tooth Gene Identified].
Message posted by: Trevor M. D'Souza