Friday, June 01, 2012

My most favorite toxin..... melittin

 I missed out on the fun! Last week there was a toxin carnival at Sciencegeist and I wasn't aware of it. It inspired me, however, to think of a toxin I would be interested in researching. I knew immediately what my choice would be: bee venom. (I don't think anyone covered this topic but I only perused quickly through the articles listed.)

Bee venom has always fascinated me. How is it that a  tiny, tiny creature like a bee can land on a person and create such an excruciatingly painful welt on their skin? It amazes me that such a miniscule, otherwise insignificant creature can do such a thing. So- I want to know more about the chemistry of how it happens.

It turns out that the chemical causing pain in these pesky and painful bee stings is called melittin. It would be logical to assume that, given the small amount of bee venom injected by the teeny, tiny pest that it would be 100% melittin. Wrong! Only about half of the approximately 0.1 mg of toxin is actually the toxic compound itself. The rest are other peptides which contribute to the strong Ouch! of pain but none more than the melittin itself.

Melittin has a tetramer structure. What? You might ask. What is a tetramer? I asked the same question in my 400-leve inorganic class during undergrad when we had finally graduated to naming complex compounds. A tetramer structure is a repeating structure of  four base units (in this case peptides made of amino acids). (Hence the prefix "tetra") (If you study enough chemistry you begin to realize the utmost importance of memorizing your Greek and Latin prefix and suffix terms. It is one of the many times in science that a mastery of the English language comes in very handy.)  The tetrameric structure may seem insignificant until you realize that it greatly influences the overall function of the molecule.

If you are a beginner (and I expect my readers to mostly be beginners) then I would suggest you visit my post about how soap works before you read on. This molecule has the polar/nonpolar properties in common with the soap/water/grease situation which is a simplified version of how this molecule works.

Basically, the way the alpha-helical monomers are structured, their polar outsides and nonpolar insides allow the molecule to penetrate phospholipids and interfere with critical body processes like the sodium/potassium channels that allow production of ATP.  But- just like many toxins, this capability can be used in a positive way for medicinal purposes.

Melittin is currently being researched for its ability to fight diseases like lyme disease. It is also being investigated as a possible cure for cancer. Apparently they are developing a nano-device to deliver the melittin to specific areas of the body  in order to avoid exposure of the chemical to healthy tissue.

So whether you come in contact with melittin by accident (and a small Ouch! of pain) or via the purposeful hand of a healing doctor (let's hope not) this "toxin" is versatile to say the least!

The Triple Helix Online: Sweeter than Honey by  Colleen Thurman, Dec  7, 2009
Thomas C. Terwilligert and David Eisenbergg. The Structure of Melittin. The Journal of Biological Chemistry.  1982, Vol 257 No 11, 6016-6022.