Sweet-tasting proteins

Brazzein is another small sweet-tasting protein whose solution structure has been recently solved by NMR. Brazzein tastes 2000 times sweeter than sucrose on a weight basis and is exceptionally thermostable. As indicated by NMR, the structure of this 54 residue, single-chain polypeptide does not change between 32 and 82 °C and retains its sweetness after incubation at 98 °C for two hours.Brazzein contains one a-helix and three strands of antiparallel jd-sheet stabilized by four intramolecular disulphide bonds. It has been proposed that the disulphide bonds could be responsible for the thermostability of brazzein by forming a compact structure at the tertiary level.The structure of brazzein does not resemble that of the other two sweet proteins with known structures, monellin and thaumatin, whereas sequence alignment and structural prediction indicate that brazzein shares the fold of a newly identified family of serine proteinase inhibitors. 

Van der Wei H, Loeve K, Isolation and characterization ofThaumatin I and II, the sweet tasting proteins from Thaumatococcus danieUii Benth, Eur J Biochem 31 221-225, 1972. 

Cornelissen, B., Hooft van Huijsduijnen, R. Bol, J. (1986). A tobacco mosaic virus-induced tobacco protein is homologous to the sweet-tasting protein thaumatin. Nature 321, 531-2. 

The occurrence of sweet-tasting proteins, such as thaumatin, monellin, mabinlin and pentadin, in the pulp of fruits of various rain forest species has been reported. The sweet-tasting proteins have different molecular lengths (from 54 residues of brazzein to 207 residues of thaumatin), virtually no sequence homology and very little structural homology. Thaumatin, the most characterised sweet protein, is 100,000 times sweeter than sugar on a molar... 

Pentadin is a sweet-tasting protein that was isolated from the fruit of Oubli (P bmzzecma Baillon), a climbing shrub that is native to West African countries. Pentadin s molecular mass is estimated to be 12kDa. It is reported to be 500 times sweeter than sucrose on a weight basis. The primary structure has not yet been determined, although amino acid analyses were carried out.91... 

Synergistic effects between MSG and sodium chloride have also been reported [8], For maximum palatability of a clear soup, more MSG must be added if only small amounts of salt are used, and vice versa. Optimum amounts of salt and MSG are 0.8 % and 0.4 %, respectively. Thaumatin, an intensely sweet tasting protein has been reported to have a similar synergistic effect to that of 5 -ribonucleotides on MSG, but at significantly lower dosages [8]. Other umami substances with synergistic effects on each other include various amino acids (e.g. L-cysteine, D,L-homocysteine, cysteine S-sulfonate), polypeptides, cycloalliin, and histamine [8]. 

Curculin The sweet taste of curculin disappears in a few minutes after holding it in the mouth. Then, water elicits the sweet taste again and black tea tastes like sweetened tea. In addition, curculin modifies sour into sweet taste (like miraculin). Sweet tasting protein (molecular weight 28,000) isolated from the fruits of Curculigo latefolia. 

Thaumatin (trade name Talin ) Masks bitter taste. Sweet tasting protein (molecular weight 22,000) isolated from the fruit of the West African perennial plant Thau-matoccus danielli. Although the primary taste property of thaumatin is sweetness, its main use is as a flavour modifier. 

Faus I (2000) Recent developments in the characterization and biotechnological production of sweet-tasting proteins. Appl Microbiol Biotechnol 53 145-151 Fisher GL, Pfaffmann C, Brown E. (1965) Dulcin and saccharin taste in squirrel monkeys, rats, and men. Science 150 506... 

Assadi-Porter, F.M., Aceti, D.J., and Markley, J.L. (2000). Sweetness determinant sites of brazzein, a small, heat-stable, sweet-tasting protein. Arc/r. Biochem. Biophys. 376, 259-265. 

Bodani, U.C., Anchin, J.M., and Linthicum, D.S. (1993). Monoclonal antibodies to sweet taste proteins, IL Development of two different immunoassays for thaumatin and monellin. Hybridoma 12,177-183. 

Caldwell, J.E., Abildgaard, F., Dzakula, Z., Ming, D., HeUekant, G., and Markley, J.L. (1998). Solution structure of the thermostable sweet-tasting protein brazzein. Nat. Struct. Biol. 5, 127 431. 

Murzin, A.G. (1993). Sweet-tasting protein monellin is related to the cystatin family of thiol proteinase inhibitors. J. Mol. Biol. 230, 689-694. 

Slootstra, J.W., De Geus, P., Haas, H., Verrips, C.T., and Meloen, R.H. (1995). Possible active site of the sweet-tasting protein thaumatin. Chem. Senses 20, 535-543. 

Sweet proteins, proteins and peptides that elicit sweet taste. Thaumatin, mondlin, mabinlin, brazzein, egg lysozyme, and neoculin (previously named curculin) have been identified as sweet-tasting proteins. New G protein-coupled receptors have been... 

Pentadin. Sweet-tasting protein (Mr 12000) ft-om the plant Pentadiplandra brazzeana (Pentadiplandraceae) having a 500-fold higher sweetness than sucrose. In contrast to other, protein-based sweeteners, P. is stable to heat. 

Figure 5.1. Shallenberger and Acree hypothesis for the interaction of the AH and B units of a sweet compound, with complementary groups on the sweet-tasting protein receptor.

Figure 5.2. Binding of the Shallenberger-Kier AH-B-X glucophore with the complementary AH -B -X groups at the sweet-tasting protein receptor site.

L-phenylalanine binding only two of the three complementary sites of the sweet taste protein receptors sites (NO TASTE)... 

Figure 5.4. Proposed binding of d- and L-p-glucopyranose with the three complementary binding sites of the sweet-taste protein receptor, and the binding of D-phenylalanine with the three sites, but the binding of L-phenylalanine with only two of the sites.

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