Introduction of a negative charge at Arg82 in thaumatin abolished responses to human T1R2-T1R3 sweet receptors |
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Authors: | Ohta Keisuke Masuda Tetsuya Tani Fumito Kitabatake Naofumi |
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Affiliation: | aDepartment of Natural Resources, Graduate School of Global and Environmental Studies, Kyoto University, Uji, Kyoto 611-0011, Japan;bDivision of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Uji, Kyoto 611-0011, Japan |
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Abstract: | Thaumatin, an intensely sweet-tasting protein, elicits a sweet-taste sensation at a level as low as 50 nM. Although previous sensory analyses have suggested that Lys67 and Arg82 are important to the sweetness of thaumatin, the exact effects of each residue on sweet receptors are still unknown. In the present study, various mutants of thaumatin altered at Arg82 as well as Lys67 were prepared and their sweetness levels were quantitatively evaluated by cell-based assays using HEK293 cells expressing human sweet receptors. Mutations at Arg82 had a more deteriorative effect on sweetness than mutations at Lys67. Particularly, a charge inversion at Arg82 (R82E) resulted in an abolishment of the response to sweet receptors even at a concentration as high as 1 mM. These results indicate that Arg82 plays a central role in determining the sweetness of thaumatin. A strict spatial charge location at residue 82 appears to be required for interaction with sweet receptors. |
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Keywords: | Abbreviations: HEK293, human embryonic kidney 293 CD, circular dichroism DMEM, Dulbecco&rsquo s modified Eagle&rsquo s medium FBS, fetal bovine serum HBSS, Hank&rsquo s balanced salt solution EC50, 50% effective concentration |
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