Miraculin is a glyco-protein (glyco-proteins are made of amino acids and carbohydrates).

Does it cause miracles though?!

Well, in some ways, yes it does – but only small ones.

After miraculin has been tasted, ordinarily sour foods taste sweet. However, miraculin is not sweet tasting in itself.

It is extracted from the fruit  fruit of Synsepalum dulcificum and is a heat stable water soluble substance. As you can imagine, it is being touted as a potential sweetener in food and scientists are trying to mass produce it by inserting the relevant gene into bacteria and tomatoes (recombinant DNA technology).

Image kindly reproduced according to the licence at: http://en.wikipedia.org/wiki/File:Miraculin.png

For more information on miraculin, read the article at http://en.wikipedia.org/wiki/Miraculin