Miraculin protein found in miracle fruit berries and glycoprotein

Miraculin is a plant protein that has an unusual property of changing taste by switching sour into a sweet taste. Two histidine residues, located in exposed regions, are the main responsible of the properties of miraculin. Miraculin is found in a berry called Synsepalum dulcificum.

Miraculin is a taste-modifying protein isolated from the red berries of Richadella dulcifica, a shrub native to West Africa. Miraculin by itself is not sweet, but it is able to turn a sour taste into a sweet taste.

Taste effects of miraculin
Cortical representation of taste-modifying action of miracle fruit in humans.
Neuroimage. 2006 Dec;33(4):1145-51. Yamamoto C, Nagai H, Takahashi K, Nakagawa S, Yamaguchi M, Tonoike M, Yamamoto T. Department of Behavioral Physiology, Graduate School of Human Sciences, Osaka University, 1-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
Red berries of a tropical plant called miracle fruit, Richadella dulcifica, reduce the sour and aversive taste of acids and add sweet and palatable taste. To elucidate the brain mechanism of this unique action of miracle fruit, we recorded taste-elicited magnetic fields of the human cerebral cortex. The initial taste responses were localized in the fronto-parietal opercular/insular cortex reported as the primary taste area. The mean latency of the response to citric acid after chewing miracle fruit was essentially the same as that for sucrose and was 250-300 ms longer than that for citric acid. Since it is known that stimulation with acids after the action of miracle fruit induces both sweetness and sourness responses in the primate taste nerves, the present results suggest that the sourness component of citric acid is greatly diminished at the level of subcortical relays, and mostly sweetness information reaches the cortical primary taste area. We propose the idea that the qualitative aspect of taste is processed in the primary taste area and the affective aspect is represented by the pattern of activation among the different cortical areas.

Miraculin research studies
Complete amino acid sequence and structure characterization of the taste-modifying protein, miraculin.
J Biol Chem. 1989 April. Department of Chemistry, Faculty of Education, Yokohama National University, Japan.
The taste-modifying protein, miraculin, has the unusual property of modifying sour taste into sweet taste. The complete amino acid sequence of miraculin purified from miracle fruits by a newly developed method (Theerasilp, S., and Kurihara, Y. (1988) J. Biol. Chem. 263, 11536-11539) was determined by an automatic Edman degradation method. Miraculin was a single polypeptide with 191 amino acid residues. The calculated molecular weight based on the amino acid sequence and the carbohydrate content (13.9%) was 24,600. Asn-42 and Asn-186 were linked N-glycosidically to carbohydrate chains. High homology was found between the amino acid sequences of miraculin and soybean trypsin inhibitor.

Molecular modelling of miraculin: Structural analyses and functional hypotheses.
Biochem Biophys Res Commun. 2008 Feb 29; Paladino A, Costantini S, Colonna G, Facchiano AM. Paladino A, Costantini S, Colonna G, Facchiano AM. Laboratory of Bioinformatics and Computational Biology, National Council of Researches, Institute of Food Sciences ISA - CNR, via Roma 52A/C, 83100 Avellino, Italy.
Miraculin monomer is flavourless at all pH as well as at high concentration; the dimer form elicits its taste-modifying activity at acidic pH; a tetrameric form is also reported as active. Two histidine residues, located in exposed regions, are the main responsible of miraculin activity. Since structural data of miraculin are not available, we have predicted its three-dimensional structure and simulated both its dimer and tetramer forms by comparative modelling and molecular docking techniques.

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