How the miracle fruit changes sour into sweet

This is so cool!!! I love when mechanisms are figured out at the molecular level!

http://blogs.discovermagazine.com/notro ... Science%29
How the miracle fruit changes sour into sweet
September 26th, 2011
by Ed Yong

Image by Hamale Lyman

To understand why the berry gets its name, you need to eat something acidic. The berries have the ability to make sour foods taste deliciously sweet. Munch one, and you can swig vinegar like it was a milkshake, or bite lemons as if they were candy.

The secret to the fruit’s taste-transforming powers is a protein called miraculin. Thanks to their efforts, we know a lot about the protein’s structure, and how acidity, temperature and dose affect its taste-altering powers.

The general idea is that miraculin changes the shape of proteins on our tongues called sweet receptors. Koizumi’s... showed that miraculin does stick directly to sweet receptors, and it latches on more strongly than do other conventional sweeteners like aspartame or saccharin. In neutral conditions, neither acidic nor alkaline, miraculin stops these other sweeteners from getting a hold on the sweet receptors. It actually represses the receptors, stopping them from doing their job. Under acidic conditions, the opposite happens – miraculin supercharges the sweet receptors. It distorts them into an active shape, while also making them extra-sensitive to sweeteners like aspartame.

Here, then, is what happens when you chomp on a miracle berry. Miraculin sits on your sweet receptors for an hour or so. For most of that time, it silences the receptors, which is why the fruit itself tastes of very little. Whenever you take a bite or swig of something acidic, miraculin gains a few extra protons and changes shape. In doing so, it also changes the shape of the sweet receptors it has stuck to, sending them into a signalling frenzy.

Some general knowledge of receptors:
Receptors often have multiple "ligands" - those molecules that bind to receptors and either activate or deactivate them. Because these ligands are competing for essentially the same, or nearby, binding sites on the receptor, they will affect whether other ligands can or cannot bind (because when a ligand binds to a receptor, it changes the physical shape of the receptor, which distorts other binding sites on the receptor for other ligands); thus affecting what happens inside the cell once the receptor is activated. Even more cool is what happens to the receptor once bound by a ligand - some remain embedded within the cell wall and the physical change causes them to release molecules that are bound to the receptors on the inside of the cell which then float freely off to instigate changes; whereas other receptors become internalized wholly within the cell, leaving the outer cell wall, and traveling around to effect change - often to the nucleus where they set off transcription of DNA into RNA which creates proteins that go do the work in the cell. Cascade effects can be very complicated and messy, with interactions happening between other pathways that are activated - there's always stuff going on inside cells!
see her for more info if you're interested: http://en.wikipedia.org/wiki/Receptor_% ... emistry%29
http://en.wikipedia.org/wiki/Signal_transduction

Reference: Koizumi, Tsuchiya, Nakajima, Ito, Terada, Shimizu-Ibuka, Briand, Asakura, Misaka & Abe. 2011. Human sweet taste receptor mediates acid-induced sweetness of miraculin. PNAS
http://www.pnas.org/content/early/2011/09/16/1016644108

Grady wrote: geek

:Thank You:

On a personal, well-known note about me, I detest biochemistry - having to learn how to design experiments that would let you know the difference between competitive antagonists, non-competitive antagonists, and uncompetitive antagonists , full agonists, partial agonists, and inverse agonists, and interpret the results of the graphical data were such an bane to my existence that my brain refused to absorb the info - I never got above a C in the 3 biochemistry classes I took, undergrad or graduate. I think it's cool as hell, but I don't want to ever research it!