Molecular mechanisms of the action of miraculin, a taste-modifying protein.

Miraculin (MCL) is a homodimeric protein isolated from the fruits of Richadella dulcifica, a shrub native to West Africa. Although it is flat in taste at neutral pH, MCL has taste-modifying activity in which sour stimuli produce a sweet perception. Once MCL enters the mouth, strong sweetness can be detected for more than 1 h each time we taste a sour solution. While the human sweet taste receptor (hT1R2-hT1R3) has been identified, the molecular mechanisms underlying the taste-modifying activity of MCL remain unclear. Recently, experimental evidence has been published demonstrating the successful quantitative evaluation of the acid-induced sweetness of MCL using a cell-based assay system. The results strongly suggested that MCL binds hT1R2-hT1R3 as an antagonist at neutral pH and functionally changes into an agonist at acidic pH. Since sweet-tasting proteins may be used as low-calorie sweeteners because they contain almost no calories, it is expected that MCL will be used in the near future as a new low-calorie sweetener or to modify the taste of sour fruits.