Protein Monellin

Exotic proteins Monellin Resilin Glue proteins... 

That the initial event of taste stimulation takes place on the cell surface of the taste receptor is now universally accepted. In addition, accumulated evidence strongly suggests that taste-bud stimulation is extracellular in nature. For example, (1) the sweet-taste response is both rapid and reversible, (2) the intensely sweet proteins monellin" and thaumatin could not possibly penetrate the cell, because of their size, and (3) miraculin, the taste-modifying glycoprotein, having a molecular weight of 44,000 would also be too large to penetrate the taste cell. ... 

Additional evidence that the exterior surface of the taste receptor cell plasma membrane is the location of the sweet receptor is provided by the action of the chemostimulatory proteins, monellin and thaumatin. Monellin occurs in the fruit of the African serendipity berry (Dioscoreophyllum cumminsii), and thaumatin is found in the fruit of Thaumatococcus daniellii, also... 

Xu J, Toptygin D, Graver KJ, Albertini RA, Savtchenko RS, Meadow ND, Roseman S, Callis PR, Brand L, Knutson JR. Ultrafast fluorescence dynamics of tryptophan in the proteins monellin and iiaglc. J. Am. Chem. Soc. 2006 128 1214-1221. 

Interestingly, the human TAS1R2/TAS1R3, but not its mouse counterpart, are sensitive to the sweet proteins monellin, thaumatin, and brazzein, and to the artificial sweeteners neo-tame, cyclamate, and aspartame (9-11). This difference provides a molecular explanation for the previous observation that these compounds are sweet for humans but not attractive to rodents (9). The species difference also applies to the inhibitor lactisole that blocks the sweet taste in humans but not in rats, and only inhibits the response of human TAS1R2/TAS1R3 to sweet stimuli (9). 

Brockhoff A, Behrens M, Massarotti A, Appendino G, Meyerhof W (2007) Broad tuning of the human bitter taste receptor hTAS2R46 to various sesquiterpene lactones, clerodane and lab-dane diterpenoids, strychnine, and denatonium. J Agric Food Chem 55 6236-6243 Brouwer JN, Hellekant G, Kasahara Y, van der Wei H, Zotterman Y (1973) Electrophysiological study of the gustatory effects of the sweet proteins monellin and thaumatin in monkey, guinea pig and rat. Acta Physiol Scand 89 550-557... 

Ariyoshi, Y., and Kohmtira, M. (1994). Solid-phase synthesis and structure-activity relationships of analogs of the sweet protein monellin. J. Soc. Synth. Org. Chem. Jpn. 52,359-369. 

Kohmura, M., Nio, N., and Ariyoshi, Y. (1992). Highly probable active site of the sweet protein monellin. Biosci. Biotechnol. Biochem. 56,1937-1942. 

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

Some proteins display rather exotic functions that do not quite fit the previous classifications. Monellin, a protein found in an African plant, has a very sweet taste and is being considered as an artificial sweetener for human consumption. Resilin, a protein having exceptional elastic properties, is found in... 

In a study of the three-dimensional structure of thaumatin, it was reported that, not only do antibodies raised against thaumatin cross-react with monellin,but antibodies raised against monellin also cross-react with thaumatin, suggesting that there is some structural similarity between portions of the two sweet-protein molecules. Earlier studies " had shown that there is a limited homology in the amino acid sequence in the two proteins. Five tripeptides in monellin have their counterparts in thaumatin. 

The design of safe sweeteners is very important for people who are afiected by diabetes, hyperlipemia, caries and other diseases that are linked to sugar consumption. Sweet proteins, which are found in several tropical plants, are many times (100-100,000) sweeter than sucrose on a molar basis. Only a few sweet proteins are known miraculin, monellin, thaumatin, curculin, mabinlin. 

Native monellin consists of two polypeptide chains, a 45-residue A-chain and a 50-residue B-chain, linked by non-covalent interactions. At neutral pH, it is fairly resistant to heat denaturation with a higher than 80 °C. The crystal structure of native monellin shows a tertiary structure comprising an anti-parallel /1-sheet with five strands and an a-helix. H NMR spectroscopy and hydrogen exchange methods have been used to characterize the alcohol-denaturated state of monellin in order to understand how its secondary structure depends on environmental conditions. " Structural and dynamic studies by NMR have been carried out in order to compare native monellin and a non-sweet analogue in which Asp was replaced by Abu . The three-dimensional structures of the two proteins are found to be very... 

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. 

There are seven known sweet and taste-modifying proteins, namely (1) monellin and (2) thaumatin (3) mabinlin. and (4) curculin (5) pentadin, (6) brazzein and (7) miraculin.The properties and characteristics of these proteins are illustrated in Table 2. There are several recent reviews relating to sweet proteins. Apart from curculin and... 

Of course, the goal of every synthetic organic chemist is to obtain crystalline products, and a few cases of crystalline synthetic proteins have been reported. These include the ribonuclease A synthesized in solution/35 which crystallized after chemical workup and affinity chromatography (see Section 5.1.6.2.2). Further examples include an HIV protease analogue/701 a ubiquitin analogue/59 and monellin/89 which were each prepared by solid-phase methods and purified by HPLC. 

Unusual proteins are also characteristic of the biome free-sulfydryl type for both tropical Americas and the East, and taste-modifying type, like miraculin, monellins, and thaumatin, for tropical Africa. 

Figure 30-31 Structures of some very sweet compounds. The backbone structure of the protein thaumatin I is included. The main body of this structure consists of two (3 sheets forming a flattened (3 barrel. (3 Strands in the top sheet are shaded light, and those in the bottom sheet are darker. Open bars represent disulfide bonds, and the regions with sequences homologous to monellin are indicated by the hatched marks. From de Vos et al.9i0...

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... 

Monellin is a sweet protein that was isolated from the fruit of Dioscoreophyllum cumminsii (Staff Diels, which is known as the serendipity berry and is native to West Africa. It is a basic protein with an isoelectric point of approximately 9.3 and is 3000 times sweeter than sucrose.65 66 Perception lasts for more than 1 h and leaves an aftertaste. Heat denatures monellin proteins they lose their sweetness when heated over 50 °C at low pH. Monellin has a molecular mass of 10.7 kDa. Monellin has two noncovalently associated polypeptide chains chain A contains 44 amino acid residues and chain B has 50 residues. In 1976, the primary structure of monellin was proposed independently by three groups but their results all differed somewhat.67-69... 

Brazzein is a sweet protein that was isolated from the fruit of the West African climbing plant Oubli (Pentadiplandra brazzeana Baillon). Along with pentadin, which was discovered in 1989, brazzein is the second sweet protein that was discovered in this fruit. Like other natural sweet proteins such as monellin and thaumatin, it is highly sweet. On a weight basis, brazzein is 500 times sweeter than sucrose when compared to 10% sucrose solution and 2000 times sweeter when compared to 2% sucrose solution. Its sweet perception is more similar to that of sucrose than that of thaumatin, and it presents a clean sweet taste with a lingering aftertaste. Brazzein is stable over a broad pH range from 2.5 to 8 and is heat stable at 80 °C for 4h.84... 

Monellin Dioscoreophyllum cumminsii (serendipity Sweet protein... 

Single-chain Monellin (= MNEI Monellin B-Gly-Phe-Monellin A)] (94 aa, lOkDa protein) Synthetic Sweet ( = Monellin)... 

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