Snapshot Issue 23 June 2006

The T1R2 receptor

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".

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

L'édition française de cette chronique est disponible dans l'Instantanés du mois de Prolune.

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