Sweeteners monellin

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... 

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. 

An engineered single-chain monellin (SCM) constructed by fusing the two chains, A and B, covalently has been proved to retain all of the sweetening power and has a greater thermal stability.SCM was studied by NMR both in solution (Fig. and in the solid-state. Several SCM mutants were... 

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). 

Several plant-derived proteins have been reported previously as sweeteners, inclusive of curculin [103], mabinlin [104,105], monellin [28,106], pentadin [107], and thaumatin, with the latter compound already mentioned as having commercial use as a sweetener and flavor enhancer [22]. Recently, a sixth sweet protein of plant origin, brazzein, was isolated from the fruits of an African climbing vine, Pentadiplandra... 

Do these diverse compounds give rise to a common perception of sweetness or to qualitatively different sensations Sweetness does indeed appear to be a unitary percept (Breslin et al. 1994,1996). However, some sweeteners may be discriminable on the basis of their activation of other sensory transduction mechanisms or differences in the temporal properties of their sensory action. For example, the sweetener sodium saccharin activates bitter receptors in some people (Kuhn et al. 2004 Pronin et al. 2007), and also inhibits sweet taste at high concentrations (Galindo-Cuspinera et al. 2006). Sweet proteins such as thaumatin and monellin can have a slow onset or evoke a prolonged sweetness compared with sugars (Faus 2000), likely owing to a relatively high affinity for the sweet taste receptor. 

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