The T1R2 receptor

by Séverine Altairac

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Though a dog would wag a tail for a biscuit, a cat would just turn its snout up in disgust. It all has to do with taste buds...or to be more precise with a protein which is involved in the taste mechanism: T1R2. T1R2 is an integral part of the sweet receptors, which direct the perception of sweetness to the brain. Other tastes, such as a salty taste, or a bitter, acid and umami taste - which is mainly perceived by the Asians - also have their specific taste receptors, all of which are distributed on the tongue's surface, in the taste buds.

What is specific to cat sweet receptors? In all mammals - humans included - the sweet receptors are an assembly of two proteins: T1R2 and T1R3. Both are G-protein coupled receptors that are lodged in the membranes of the taste cells within the taste buds. In felines - such as cats, cheetahs and tigers - the sweet receptor is faulty: there is no T1R2, despite the fact that their genome carries the gene. But the gene is defective and, as a result, T1R2 cannot be synthesized. Consequently, the feline sweet taste receptor lacks T1R2 and cats are not able to perceive anything sugary.

So it is less a question of finding sugar distasteful than simply not being able to taste it at all. And feline behavior is modified accordingly: they show no interest whatsoever in anything sweet. This does not imply, however, that cats do not tolerate sugar. They do and they get it - and hence their energy source - in the form of glycogen via the meat they eat. This 'no sweet taste' trait seems only to be specific to felines; dogs and bears, for instance, would kill for a biscuit or some honey. So - though irresistible it may seem to you - there is no point in offering your cat a piece of cake. It's just a matter of proteins.

Also read: "The taste experience".

UniProt cross references
Taste receptor type 1 member 3 (T1R3), Felis silvestris catus (cat): Q49KI5
Taste receptor type 1 member 2 (T1R2), Homo sapiens (human): Q8TE23
Taste receptor type 1 member 3 (T1R3), Homo sapiens (human): Q7RTX0
Protein Spotlight (ISSN 1424-4721) is a monthly review written by the Swiss-Prot team of the SIB Swiss Institute of Bioinformatics. Spotlight articles describe a specific protein or family of proteins on an informal tone. Follow us: Subscribe · Twitter · Facebook