The cysteine-rich domain of human T1R3 is necessary for the interaction between human T1R2–T1R3 sweet receptors and a sweet-tasting protein, thaumatin

► The interaction between thaumatin and chimeric human–mouse T1Rs was evaluated. ► The responses to sweet receptors differed between thaumatin and other sweeteners. ► The CRD of human T1R3 is important for the interaction with thaumatin. Thaumatin is an intensely sweet-tasting protein perceived by humans but not rodents. Its threshold value of sweetness in humans is 50 nM, the lowest of any sweet-tasting protein. In the present study, the sites where sweet receptors interact with thaumatin were investigated using human embryonic kidney 293 (HEK293) cells expressing the sweet receptors T1R2–T1R3. Chimeric human– mouse sweet receptors were constructed and their responses to sweeteners were investigated. The human (h) T1R2– mouse (m) T1R3 combination responded to sucralose but not to thaumatin, clearly indicating that a T1R3 subunit from humans is necessary for the interaction with thaumatin. Furthermore, results obtained from using chimeric T1R3s showed that the cysteine-rich domain (CRD) of human T1R3 is important for the interaction with thaumatin. The CRD of T1R3 would be a prominent target for designing new sweeteners.