Team:Brown/Project

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Revision as of 18:21, 13 July 2010

Project 1 - TAT-PTD

Project Description

Progress

Project 2 - Quad-state light-activation

Project Description

Progress

Project 3 - Miracle Yogurt

Background

In the early eighteenth century, French cartographer and navigator Chevalier des Marchais travelled all along the west coast of Africa. His maps and manuscripts were published after his death by Père J. B. Labat in Amsterdam in 1730-31. One of these, from 1725, documented a peculiar food culture among local tribes, who consumed tiny red berries before most meals.

These berries are known as Synsepalum dulcificum, Richadella dulcifica, or colloquially ‘miracle fruit’. They have a peculiar quality: for 30 minutes to two hours after consumption, sour foods are perceived as sweet. This fascinating property was not rediscovered until the mid-19th century, when Prof. Kenzo Kurihara, a Japanese scientist, published an article in Science about the isolation of the active compound, which he coined miraculin.

Soon afterward, Robert Harvey and Don Emery became co-founders of a miracle berry start-up called Miralin. In 1974, the FDA cut support for the company and halted the approval of miracle berries as a harmless food additive only weeks after the Miralin offices were raided by an unknown party. Although the identity of the thieves was never determined, claims have been made that the raid and subsequent FDA disapproval were supported by high-ups in the sugar and sweetener industry.

Today, miracle berries are making an underground comeback thanks to a few small startups, with slogans such as mBerry’s “Make life sweeter.” In the last few years, their popularity has grown exponentially, and it’s all thanks to a single protein named miraculin.

Miraculin is a small glycoprotein, 191 amino acids long, that was first sequenced in 1989. Almost 14% of the protein’s weight is made up of various sugars, but these are not necessary for the taste-modifying effects. In miracle berries, miraculin occurs as a tetramer, more specifically a combination of two homodimers. Within these dimers, two miraculin monomers are bound together by a disulfide bridge. Miraculin is readily soluble in aqueous solution and is heat stable up to 100°C. It is active at pH 3-12, and can remain stable and active at pH 4 for 6 months in a refrigerated environment.

Unlike similar taste-modifying proteins, miraculin does not intrinsically possess a sweet taste, however the maximum sweetness response induced by miraculin has been shown equivalent to 17% sucrose solution (very sweet). The mechanism of miraculin’s taste-modifying properties has not yet been conclusively determined. Mutation experiments suggest that two histidine residues (His29 and His59) are mainly responsible for these properties. Both histidine residues are involved in dimerization. It is hypothesized that one site acts to attach miraculin to the cell membranes of the sweet tastebuds. The other induces a conformational change in response to protonation (acids, the major components of sour taste, are proton donors) that brings miraculin in contact with an active site of a receptor on the surface of the tastebud cell.

Together, these cause miraculin to bind transiently to the tastebud and induce activation of the sweetness response when in the presence of sour acids. The ability of the fruit to turn non-sweet foods into sweet foods without a caloric penalty is highly valuable, and alone provides a reason to mass-produce miraculin-containing miracle fruit. Synsepalum dulcificum, however, is not a practical plant to mass-produce. Its seeds have a 24% sprouting success rate, and the young plants require high humidity and partial shade. They do not bear fruit for the first 2-3 years, and only crop out twice a year. What’s more, it takes 2-3 berries worth of pulp to yield one ‘dose’. These limitations make miraculin an excellent candidate for production in transgenic organisms.

If miraculin, tagged with a secretion signal, can be successfully inserted into L. lactis, it will result in an extraordinarily cheap and easily distributable mechanism for the mass-production of miraculin-containing yogurt, buttermilk, or cheese. To make yogurt, a small amount of active yogurt or dehydrated lactobacillus is added to milk and incubated at 38C for seven hours. Dehydrated bacteria can be easily shipped by mail, and a small amount of previously-made yogurt can be used as a starter culture for further production.

This yogurt would prove valuable for a number of populations: diabetics who cannot consume overly sugary foods, dieters who want to lose weight but cannot stick to their bland diets, cancer patients whose chemotherapy leaves a bitter, metallic taste (a pilot study has indicated that miracle berries counteract this effect), children who cannot stand the taste of bitter/sour foods, and foodies who seek a novel perceptual experience. By increasing consumption of probiotic cultures and decreasing consumption of high-calorie sugars and carcinogenic artificial sweeteners such as aspartame, the mass production and distribution of a miraculin-containing yogurt could provide a healthier lifestyle.

Project Description

We plan to insert the miraculin gene, along with a secretion tag, into Lactococcus lactis. This will be done via a hybrid E.coli/Lactobacillus shuttle vector pPTPi.