Sweet enhancing effect of neohesperidin dihydrochalcone (NHDC) or cyclamate has been reported to be
synergistic in human sensory tests. However, little is known about whether these synergisms are caused
by the mechanism mediated by the human sweet-taste receptor. Here, we examined the sweetness
intensity of sweet tastant mixtures by measuring the responses of cultured cells stably expressing the
human sweet-taste receptor. The results showed that the cell response to sucrose was synergistically
potentiated by the addition of NHDC or cyclamate. Moreover, a point mutation in the transmembrane
domain of hT1R3 almost completely eliminated the enhancing effects of NHDC and cyclamate. These
results suggest that ligand–receptor interactions in the transmembrane domain of hT1R3 are necessary
for NHDC and cyclamate to elicit the synergistic potentiation of the receptor activation. Our results
may provide the foundation of a molecular basis for receptor-based synergisms of sweet tastes in mixtures
of diverse sweet substances