Production of Sweet Protein Transgenics with Monellin
Sweet proteins can replace artificial sweeteners, since they are natural sweeteners with low calories. Monellin, a naturally sweet Dioscoreophyllum cumminsii protein, produces sweet flavor, because carbohydrate has been proved to be important to its sweet taste. It is a heterodimeric protein that loses its activities during denature with its 94 amino acid residues with a molecular weight of 10.5 kDa. A promising sweetener that tastes sweet at pH 29 is proposed for Monellin, while high pH or heating after 70 or higher could denature this protein. Structural studies showed that the relation between these two subunits gives stability to this heterodimer monellin as opposed to the indena. Monellin composed of one single polypeptide also has a flavor that is equivalent to the double-chain monellin. As flavor enhancer and high intensity sweetener, Monellin offers dual applications and was recommended for use in some countries. As the supply of naturally present monellin is small, its synthesis through transgenic organisms has been investigated thoroughly. Efforts were made in the different expression systems of bacterial, yeast and transgenic plants to produce this recombinant protein. Monellin development in transgenic fruit and vegetable products provides a viable approach to flavor and quality improvements. In prokaryotic (E. coli) and eukaryotic (tomato) systems, the stable and enhanced expression of synthetic sweet protein monellin has been reported. The temperature of the recombinant monellin protein remained strong and sweet over a range of temperature (up to 70?) and intense pH levels.