Miraculin

Miraculin Glycoprotein
Crystallographic structure of a dimeric miraculin like protein from seeds of Murraya koenigii.
Identifiers
Symbol	MIRA_RICDU
UniProt	P13087

Miraculin is a natural sugar substitute, a glycoprotein extracted from the fruit of Synsepalum dulcificum. The berry, also known as the miracle fruit, was first documented by explorer Chevalier des Marchais, who searched for many different fruits during a 1725 excursion to its native West Africa.

Miraculin itself is not sweet. However, after the taste buds are exposed to miraculin (which binds to sweet receptors on the tongue), acidic foods which are ordinarily sour (such as citrus) are perceived as sweet. This effect lasts up to an hour.

The active substance, isolated by Prof. Kenzo Kurihara (栗原 堅三　Kurihara Kenzō), a Japanese scientist, was named miraculin after the miracle fruit when Kurihara published his work in Science in 1968.

Miraculin was first sequenced in 1989 and was found to be a glycoprotein consisting of 191 amino acids and some carbohydrate chains.

Miraculin occurs as a tetramer (98.4 kDa), a combination of 4 monomers group by dimer. Within each dimer 2 miraculin glycoproteins are linked by a disulfide bridge.

The molecular weight of the glycoprotein is 24.6 kDa including 3.4 kDa (13.9% of the weight) of sugar constituted (on molar ratio) of glucosamine (31%), mannose (30%), fucose (22%), xylose (10%) and galactose (7%).

The taste-modifying protein, miraculin, has seven cystein residues in a molecule composed of 191 amino acid residues. Both tetramer miraculin and native dimer miraculin in its crude state have the taste-modifying activity of turning sour tastes into sweet tastes.

Miraculin, like curculin (another taste-modifying agent), is not sweet by itself, but it can change the perception of a sour beverage into a sweet beverage, even for a long period after consumption. The anti-sweet compound Gymnemic acid suppresses the sweet taste of miraculin, like it does for sucrose. The duration and intensity of the taste-modifying phenomena depends on various factors — miraculin concentration, duration of contact of the miraculin with the tongue, and acid concentration. Maximum sweet-induced response has been shown to be equivalent to the sweetness of 17% sucrose solution.