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ABSTRACT:Thaumatin is frequently used as a model protein in crystallization studies because it rapidly forms crystals in the presence of tartrate ions. The thermodynamic and kinetic properties of thaumatin crystals have been studied for almost 10 years, and the results are contradictory. Here we show that by using a homogeneous preparation of thaumatin and controlling the stereochemistry of the tartrate precipitant, it is possible to achieve consistent results for the protein solubility. To understand the role of protein impurities in the crystallization of thaumatin, we examined two commercial sources of the protein and characterized the heterogeneities therein. To examine the effect of precipitant stereochemistry, we crystallized thaumatin with L, D, and DL (racemic) tartrate ions. We suggest that the inconsistencies among previous results stem in part from the different behavior of thaumatin with the L and D enantiomers: the solubility of thaumatin crystals increases with temperature in L-tartrate, whereas it decreases with temperature in D-tartrate. Our results demonstrate the importance of using pure protein and stereochemically pure precipitants in the crystallization of proteins.
ABSTRACT:Thaumatin is frequently used as a model protein in crystallization studies because it rapidly forms crystals in the presence of tartrate ions. The thermodynamic and kinetic properties of thaumatin crystals have been studied for almost 10 years, and the results are contradictory. Here we show that by using a homogeneous preparation of thaumatin and controlling the stereochemistry of the tartrate precipitant, it is possible to achieve consistent results for the protein solubility. To understand the role of protein impurities in the crystallization of thaumatin, we examined two commercial sources of the protein and characterized the heterogeneities therein. To examine the effect of precipitant stereochemistry, we crystallized thaumatin with L, D, and DL (racemic) tartrate ions. We suggest that the inconsistencies among previous results stem in part from the different behavior of thaumatin with the L and D enantiomers: the solubility of thaumatin crystals increases with temperature in L-tartrate, whereas it decreases with temperature in D-tartrate. Our results demonstrate the importance of using pure protein and stereochemically pure precipitants in the crystallization of proteins.
Thaumatin, an intensely sweet-tasting protein used as a sweetener, was secreted by the methylotrophic yeast Pichia pastoris. Approximately 100 mg L -1 of recombinant thaumatin I was obtained using an expression vector which possesses three copies of the thaumatin gene containing the 22-amino acid presequence. Expression yield was about three-fold higher than when the α-factor secretion signal from Saccharomyces cerevisiae was used. The circular dichroism and tryptophan fluorescence spectra for recombinant thaumatin I were almost the same as those for plant thaumatin. Large amounts of homogeneous recombinant thaumatin allowed for preparation of high-quality crystals in the presence of cryoprotective glycerol used in high-resolution x-ray structural analysis to help further understand the perception of the sweet taste of thaumatin.
The article contains sections titled: 1. Introduction 2. Sensory Properties 2.1. Structural Requirements for Sweetness 2.2. Sweetness Intensity 2.3. Taste Characteristics 2.4. Synergism 3. Uses 3.1. Foods and Beverages 3.2. Table‐Top Sweeteners 3.3. Cosmetics 3.4. Pharmaceuticals 3.5. Feed 3.6. Others 4. General Toxicology and Physiology 4.1. Toxicology 4.2. Metabolism 4.3. Suitability for Diabetics 4.4. Dental Effects 5. Food Legislation 5.1. International Regulations and Assessments 5.2. National Food Legislation 6. Substances Commonly Used as Sweeteners 6.1. Acesulfame K 6.1.1. General Information 6.1.2. Physical and Chemical Properties 6.1.3. Production 6.1.4. Specifications and Analysis 6.1.5. Toxicology and Legislation 6.1.6. Uses 6.2. Aspartame 6.2.1. General Information 6.2.2. Physical and Chemical Properties 6.2.3. Production 6.2.4. Specifications and Analysis 6.2.5. Toxicology and Legislation 6.2.6. Uses 6.3. Cyclamate 6.3.1. General Information 6.3.2. Physical and Chemical Properties 6.3.3. Production 6.3.4. Specifications and Analysis 6.3.5. Toxicology and Legislation 6.3.6. Uses 6.4. Saccharin 6.4.1. General Information 6.4.2. Physical and Chemical Properties 6.4.3. Production 6.4.4. Specifications and Analysis 6.4.5. Toxicology and Legislation 6.4.6. Uses 7. Sweeteners of Lesser Importance 7.1. Glycyrrhizin 7.1.1. General Information and Properties 7.1.2. Production 7.1.3. Toxicology and Legislation 7.1.4. Uses 7.2. Neohesperidin Dihydrochalcone 7.2.1. General Information and Properties 7.2.2. Production 7.2.3. Toxicology and Legislation 7.2.4. Uses 7.3. Stevioside and Rebaudioside 7.3.1. General Information and Properties 7.3.2. Production 7.3.3. Toxicology and Legislation 7.3.4. Uses 7.4. Sucralose 7.4.1. General Information and Properties 7.4.2. Production 7.4.3. Toxicology and Legislation 7.4.4. Uses 7.5. Thaumatin 7.5.1. General Information and Properties 7.5.2. Production 7.5.3. Toxicology and Legislation 7.5.4. Uses 8. New Developments 8.1. Alitame 8.2. Others 9. Substances Formerly Used as Sweeteners 9.1. Dulcin 9.2. Others
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