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Masuda T, Suzuki M, Yamasaki M, Mikami B. Subatomic structure of orthorhombic thaumatin at 0.89 Å reveals that highly flexible conformations are crucial for thaumatin sweetness. Biochem Biophys Res Commun 2024; 703:149601. [PMID: 38364680 DOI: 10.1016/j.bbrc.2024.149601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2024] [Accepted: 01/29/2024] [Indexed: 02/18/2024]
Abstract
Thaumatin is a sweet-tasting protein that elicits a sweet taste at a threshold of approximately 50 nM. Structure-sweetness relationships in thaumatin suggest that the basicity of two amino acids residues, Arg82 and Lys67, are particularly responsible for sweetness. Using tetragonal crystals, our structural analysis suggested that flexible sidechain conformations of these two residues play an important role in sweetness. However, in tetragonal crystals, Arg82 is adjacent to symmetry-related residues, and its flexibility is relatively restrained by the crystal packing. To reduce and diminish these symmetry-related effects, orthorhombic crystals were prepared, and their structures were successfully determined at a resolution of 0.89 Å. Within the orthorhombic lattice, two alternative conformations were more clearly visible at Lys67 than in a tetragonal system. Interestingly, for the first time, three alternative conformations at Arg82 were only found in an orthorhombic system. These results suggest the importance of flexible conformations in sweetness determinants. Such subtle structural variations might serve to adjust the complementarity of the electrostatic potentials of sweet receptors, thereby eliciting the potent sweet taste of thaumatin.
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Affiliation(s)
- Tetsuya Masuda
- Department of Food Sciences and Human Nutrition, Faculty of Agriculture, Ryukoku University, 1-5 Yokotani, Seta Oe-cho, Otsu, Shiga, 520-2194, Japan; Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan.
| | - Mamoru Suzuki
- Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Masayuki Yamasaki
- Department of Food Sciences and Human Nutrition, Faculty of Agriculture, Ryukoku University, 1-5 Yokotani, Seta Oe-cho, Otsu, Shiga, 520-2194, Japan
| | - Bunzo Mikami
- Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan; Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan
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Pomon B, Zhao Y, Lai AL, Lin T, Freed JH, Abbaspourrad A. Thermal Degradation of Thaumatin at Low pH and Its Prevention Using Alkyl Gallates. Food Hydrocoll 2023; 139:108544. [PMID: 37546699 PMCID: PMC10399911 DOI: 10.1016/j.foodhyd.2023.108544] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Thaumatin, a potent sweet tasting protein extracted from the Katemfe Plant, is emerging as a natural alternative to synthetic non-nutritive sweeteners and flavor enhancer. As a food additive, its stability within the food matrix during thermal processing is of great interest to the food industry. When heated under neutral or basic conditions, thaumatin was found to lose its sweetness due to protein aggregation caused by sulfhydryl catalyzed disulfide bond interchange. At lower pH, while thaumatin was also found to lose sweetness after heating, it does so at a slower rate and shows more resistance to sweetness loss. SDS-PAGE indicated that thaumatin fragmented into multiple smaller pieces under heating in acidic pH. Using BEMPO-3, a lipophilic spin trap, we were able to detect the presence of a free-radical within the hydrophobic region of the protein during heating. Protein carbonyl content, a byproduct of protein oxidation, also increased upon heating, providing additional evidence for protein cleavage by a radical pathway. Hexyl gallate successfully inhibited the radical generation as well as protein carbonyl formation of thaumatin during heating.
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Affiliation(s)
- Benjamin Pomon
- Department of Food Science, College of Agriculture and Life sciences, Cornell University, Stocking Hall, Ithaca, NY, 14853
| | - Yu Zhao
- Department of Food Science, College of Agriculture and Life sciences, Cornell University, Stocking Hall, Ithaca, NY, 14853
| | - Alex L. Lai
- Department of Chemistry, College of Arts and Sciences, Cornell University, Ithaca, NY 14853
| | - Tiantian Lin
- Department of Food Science, College of Agriculture and Life sciences, Cornell University, Stocking Hall, Ithaca, NY, 14853
| | - Jack H. Freed
- Department of Chemistry, College of Arts and Sciences, Cornell University, Ithaca, NY 14853
| | - Alireza Abbaspourrad
- Department of Food Science, College of Agriculture and Life sciences, Cornell University, Stocking Hall, Ithaca, NY, 14853
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Masuda T, Okubo K, Baba S, Suzuki M, Tani F, Yamasaki M, Mikami B. Structure of thaumatin under acidic conditions: Structural insight into the conformations in lysine residues responsible for maintaining the sweetness after heat-treatment. Food Chem 2022; 389:132996. [PMID: 35500407 DOI: 10.1016/j.foodchem.2022.132996] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Revised: 04/09/2022] [Accepted: 04/14/2022] [Indexed: 11/19/2022]
Abstract
Thaumatin is an intensely sweet-tasting protein. Its sweetness persists when heated under acidic conditions, but disappears when heated at a pH above 7.0. To clarify how the structural features of thaumatin resist insoluble aggregation during heating under acidic conditions, we analysed its crystal structure obtained at pH 4.0, 6.0, and 8.0. Simultaneously, the melting temperature (Tm) at these pH levels was determined using differential scanning fluorimetry. At pH 4.0, the Tm of thaumatin was substantially lower and the overall B-factor value of its structure was higher than those at pH 6.0. Interestingly, the relative B-factor values for most lysine residues decreased as the pH reduced. These results suggest that the overall structure at pH 4.0 becomes flexible but the relative flexibility of some regions is lower than that at pH 6.0. Thus, the reduction in relative flexibility might play an important role in preventing thermal aggregation, thereby maintaining the sweetness.
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Affiliation(s)
- Tetsuya Masuda
- Laboratory of Food Chemistry, Department of Food Sciences and Human Nutrition, Faculty of Agriculture, Ryukoku University, 1-5 Yokotani Seta Oe-cho, Otsu, Shiga 520-2194, Japan; Laboratory of Food Chemistry, Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.
| | - Kyohei Okubo
- Laboratory of Food Chemistry, Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
| | - Seiki Baba
- Structural Biology Division, Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan
| | - Mamoru Suzuki
- Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Fumito Tani
- Laboratory of Food Chemistry, Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
| | - Masayuki Yamasaki
- Laboratory of Food Chemistry, Department of Food Sciences and Human Nutrition, Faculty of Agriculture, Ryukoku University, 1-5 Yokotani Seta Oe-cho, Otsu, Shiga 520-2194, Japan
| | - Bunzo Mikami
- Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan; Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
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Ren S, Hu P, Jia J, Ni J, Jiang T, Yang H, Bai J, Tian C, Chen L, Huang Q, Lv B, Feng X, Li C. Engineering of Saccharomyces cerevisiae for sensing sweetness. Biochem Eng J 2022. [DOI: 10.1016/j.bej.2021.108239] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Tang N, Liu J, Cheng Y. Potential improvement of the thermal stability of sweet-tasting proteins by structural calculations. Food Chem 2020; 345:128750. [PMID: 33302109 DOI: 10.1016/j.foodchem.2020.128750] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2020] [Revised: 11/05/2020] [Accepted: 11/26/2020] [Indexed: 11/19/2022]
Abstract
The low thermal stability of the sweet-tasting proteins limited their applications in food industry. Improve their thermal stability is the key to developing their applications in food processing. In the present study, saturation mutagenesis was performed on 4 sweet-tasting proteins, brazzein (988 mutations), curculin (2109 mutations), monellin (1824 mutations) and thaumatin (3933 mutations), using structural calculations in order to find more thermal stable mutations. The obtained results indicated that our calculated ΔΔG value (ΔΔG < 0 stabilizing, ΔΔG > 0 destabilizing) was a good predictor for predicting changes in thermal stability caused by mutations. Moreover, mutating the negatively charged residues to the other non-negatively charged amino acids was an efficient way to improve the thermal stability of the investigated sweet-tasting proteins. In addition, some promising mutations sites were identified for improving thermal stability using mutagenesis. This study provides useful information for future protein engineering to improve the thermal stability of the sweet-tasting proteins.
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Affiliation(s)
- Ning Tang
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing Key Laboratory of Functional Food from Plant Resources, Beijing 100083, China.
| | - Jiachen Liu
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing Key Laboratory of Functional Food from Plant Resources, Beijing 100083, China
| | - Yongqiang Cheng
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing Key Laboratory of Functional Food from Plant Resources, Beijing 100083, China
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Masuda T, Okubo K, Murata K, Mikami B, Sugahara M, Suzuki M, Temussi PA, Tani F. Subatomic structure of hyper-sweet thaumatin D21N mutant reveals the importance of flexible conformations for enhanced sweetness. Biochimie 2018; 157:57-63. [PMID: 30389513 DOI: 10.1016/j.biochi.2018.10.020] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2018] [Accepted: 10/26/2018] [Indexed: 01/26/2023]
Abstract
One of the sweetest proteins found in tropical fruits (with a threshold of 50 nM), thaumatin, is also used commercially as a sweetener. Our previous study successfully produced the sweetest thaumatin mutant (D21N), designated hyper-sweet thaumatin, which decreases the sweetness threshold to 31 nM. To investigate why the D21N mutant is sweeter than wild-type thaumatin, we compared the structure of the D21N mutant solved at a subatomic resolution of 0.93 Å with that of wild-type thaumatin determined at 0.90 Å. Although the overall structure of the D21N mutant resembles that of wild-type thaumatin, our subatomic resolution analysis successfully assigned and discriminated the detailed atomic positions of side-chains at position 21. The relative B-factor value of the side-chain at position 21 in the D21N mutant was higher than that of wild-type thaumatin, hinting at a greater flexibility of side-chain at 21 in the hyper-sweet D21N mutant. Furthermore, alternative conformations of Lys19, which is hydrogen-bonded to Asp21 in wild-type, were found only in the D21N mutant. Subatomic resolution analysis revealed that flexible conformations at the sites adjacent to positions 19 and 21 play a crucial role in enhancing sweet potency and may serve to enhance the complementarity of electrostatic potentials for interaction with the sweet taste receptor.
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Affiliation(s)
- Tetsuya Masuda
- Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan.
| | - Kyohei Okubo
- Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan
| | - Kazuki Murata
- Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan
| | - Bunzo Mikami
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan
| | - Michihiro Sugahara
- RIKEN SPring-8 Center, Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan
| | - Mamoru Suzuki
- Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Piero Andrea Temussi
- Department of Basic and Clinical Neurosciences, King's College London, London, SE59RX, UK; Dipartimento di Chimica, Universita' di Napoli Federico II, Napoli, I-80126, Italy
| | - Fumito Tani
- Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan
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