Acid-induced sweetness of neoculin is ascribed to its pH-dependent agonistic-antagonistic interaction with human sweet taste receptor.

Abstract

Neoculin (NCL) is a sweet protein that also has taste-modifying activity to convert sourness to sweetness. However, it has been unclear how NCL induces this unique sensation. Here we quantitatively evaluated the pH-dependent acid-induced sweetness of NCL using a cell-based assay system. The human sweet taste receptor, hT1R2-hT1R3, was functionally expressed in HEK293T cells together with G alpha protein. When NCL was applied to the cells under different pH conditions, it activated hT1R2-hT1R3 in a pH-dependent manner as the condition changed from pH 8 to 5. The pH-response sigmoidal curve resembled the imidazole titration curve, suggesting that His residues were involved in the taste-modifying activity. We then constructed an NCL variant in which all His residues were replaced with Ala and found that the variant elicited strong sweetness at neutral pH as well as at acidic pH. Since NCL and the variant elicited weak and strong sweetness at the same neutral pH, respectively, we applied different proportions of NCL-variant mixtures to the cells at this pH. As a result, NCL competitively inhibits the variant-induced receptor activation. All these data suggest that NCL acts as an hT1R2-hT1R3 agonist at acidic pH but functionally changes into its antagonist at neutral pH.

DOI: 10.1096/fj.07-100289

Cite this paper

@article{Nakajima2008AcidinducedSO, title={Acid-induced sweetness of neoculin is ascribed to its pH-dependent agonistic-antagonistic interaction with human sweet taste receptor.}, author={Ken-ichiro Nakajima and Yuji Morita and Ayako Koizumi and Tomiko Asakura and Tohru Terada and Keisuke Ito and Akiko Shimizu-Ibuka and Jun-ichi Maruyama and Katsuhiko Kitamoto and Takumi Misaka and Keiko Abe}, journal={FASEB journal : official publication of the Federation of American Societies for Experimental Biology}, year={2008}, volume={22 7}, pages={2323-30} }