Miraculin

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The Miracle Fruit, origin of Miraculin
'Miraculin'
Identifiers
Symbol MIRA_RICDU
UniProt P13087
Other data

Miraculin is a glycoprotein extracted from the miracle fruit plant, a shrub native to West Africa (Synsepalum dulcificum or Richadella dulcifica).[1]

Local names for the plant include taami, asaa, and ledidi. Miraculin itself is not sweet, but the human tongue, once exposed to miraculin, perceives ordinarily sour foods, such as citrus, as sweet for up to an hour afterwards. This small red berry has been used in West Africa to improve the taste of acidic foods. Because the miracle fruit itself has no distinct taste, this taste-modifying function of the fruit had been regarded as a miracle.

The active substance, isolated by Prof. Kenzo Kurihara, a Japanese scientist, was named miraculin after the miracle fruit when he published his work in Science in 1968.[2]

Contents

[edit] Glycoprotein structure

Miraculin was first sequenced in 1989 and was found to be a glycoprotein consisting of 191 amino acids and some carbohydrate chains.[3]

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.[4]

SIGNAL (29) MKELTMLSLS FFFVSALLAA AANPLLSAA
1-50 DSAPNPVLDI DGEKLRTGTN YYIVPVLRDH GGGLTVSATT PNGTFVCPPR
51-100 VVQTRKEVDH DRPLAFFPEN PKEDVVRVST DLNINFSAFM PNPGPETISS
101-150 WCRWTSSTVW RLDKYDESTG QYFVTIGGVK FKIEEFCGSG FYKLVFCPTV
151-191 CGSCKVKCGD VGIYIDQKGR GRRLALSDKP FAFEFNKTVY F
Amino acids sequence of glycoprotein miraculin unit adapted from Swiss-Prot biological database of protein sequences.[5]

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%).[1]

[edit] Sweetness properties

Miraculin, unlike curculin (another taste-modifying agent), is not sweet by itself, but it can change 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. [4] 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.

Glycoprotein is sensitive to heat: when heated over 100 °C, miraculin loses its taste-modifying property. Miraculin activity is inactivated at pH below 3 and pH above 12 at room temperature. The sweet modifying effect stays at pH 4 (in acetate buffer), for 6 months at 5 °C.[1]

The detailed mechanism of the taste-inducing behaviour is still unknown. It has been suggested that the miraculin protein can change the structure of taste cells on the tongue.[6] As a result, the sweet receptors are activated by acids, which are sour in general. This effect remains until the taste buds return to normal. The two histidine residues (i.e. His29 and His59) appear to be mainly responsible for the taste-modifiying behavior.[7] One site maintains the attachment of the protein to the membranes while the other (with attached xylose or arabinose) activates the sweet receptor membrane in acid solutions. The presence of positively charged ions (Ca2+ and/or Mg2+) interferes with the binding of the active sugar of miraculin to the sweet receptor and therefore inactivates the effect.[4]

[edit] As a sweetener

As miraculin is a readily soluble protein and relatively heat stable, it is a potential sweetener in acidic food (e.g. soft drinks). Japanese researchers' more or less successful attempts to mass produce it are focused on recombinant technology. While attempts to express it in yeast, and tobacco plants have failed, researchers have succeeded in preparing genetically modified E. coli bacteria[8] and lettuce[6][9] that express miraculin. The scientists' crops resulted in 40 micrograms of miraculin per gram of lettuce leaves, which was considered a large amount.[6] Two grams of lettuce leaves produced roughly the same amount of miraculin as in one miracle fruit berry.[10]

Miraculin was denied approval for use as a sweetener by the United States Food and Drug Administration (FDA).[11][12]

Miraculin has no legal status in the European Union. However it is approved in Japan as a harmless additive, according to the List of Existing Food Additives published by the Ministry of Health and Welfare (published by JETRO).

[edit] References

  1. ^ a b c Theerasilp S, Kurihara Y (August 1988). "Complete purification and characterization of the taste-modifying protein, miraculin, from miracle fruit". J. Biol. Chem. 263 (23): 11536–9. PMID 3403544. http://www.jbc.org/cgi/reprint/263/23/11536. 
  2. ^ Kurihara K, Beidler LM (September 1968). "Taste-modifying protein from miracle fruit". Science (journal) 161 (847): 1241–3. doi:10.1126/science.161.3847.1241. PMID 5673432. 
  3. ^ Theerasilp S, Hitotsuya H, Nakajo S, Nakaya K, Nakamura Y, Kurihara Y (April 1989). "Complete amino acid sequence and structure characterization of the taste-modifying protein, miraculin". J. Biol. Chem. 264 (12): 6655–9. PMID 2708331. http://www.jbc.org/cgi/reprint/264/12/6655. 
  4. ^ a b c Kurihara Y (1992). "Characteristics of antisweet substances, sweet proteins, and sweetness-inducing proteins". Crit Rev Food Sci Nutr 32 (3): 231–52. PMID 1418601. 
  5. ^ UniProtKB/Swiss-Prot database entry P13087
  6. ^ a b c Rowe, Aaron (2006-12-07). "Super Lettuce Turns Sour Sweet". Wired Magazine. http://www.wired.com/science/discoveries/news/2006/12/72251. Retrieved on 2008-07-22. ""Sweet receptors sit on taste buds and wait for sweet molecules to come along and set them off," explained Göran Hellekant, a miraculin researcher and professor of physiology and pharmacology at the University of Minnesota. "Normally, they can only be set off by chemicals that are legitimately sweet, but miraculin may distort their shape a bit so that they become responsive to acids, instead of sugar and other sweet things."" 
  7. ^ Ito K, Asakura T, Morita Y, Nakajima K, Koizumi A, Shimizu-Ibuka A, Masuda K, Ishiguro M, Terada T, Maruyama J, Kitamoto K, Misaka T, Abe K (August 2007). "Microbial production of sensory-active miraculin". Biochem. Biophys. Res. Commun. 360 (2): 407–11. doi:10.1016/j.bbrc.2007.06.064. PMID 17592723. 
  8. ^ Matsuyama T, Satoh M, Nakata R, Aoyama T, Inoue H (April 2009). "Functional expression of miraculin, a taste-modifying protein in Escherichia coli". J. Biochem. 145 (4): 445–50. doi:10.1093/jb/mvn184. PMID 19122203. 
  9. ^ Sun HJ, Cui ML, Ma B, Ezura H (January 2006). "Functional expression of the taste-modifying protein, miraculin, in transgenic lettuce". FEBS Lett. 580 (2): 620–6. doi:10.1016/j.febslet.2005.12.080. PMID 16406368. 
  10. ^ "To Make Lemons Into Lemonade, Try 'Miracle Fruit'". Wall Street Journal. 2007-03-30. http://online.wsj.com/article_email/SB117522147769754148-lMyQjAxMDE3NzM1MDIzMjAxWj.html. Retrieved on 2008-05-28. "[...]two grams produce roughly the same effect as one miracle fruit." 
  11. ^ DM Cannon The old sweet lime Trick. The Rare Fruit Review. 1992. Vol 1. Number 2.
  12. ^ AD Kinghorn and DD Soejarto. Sweetening Agents of plant-origin. CRC Crit. Rev. Plant Sci. 1986, 4, 79-120.

[edit] See also

[edit] External links

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