Medical Mystery: Mirror Images of Amino Acids Provide Clues to Schizophrenia, Stroke and Lobster Sex (preview)

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In the chemistry of life, left-handed amino acids are the rule. Why does nature make so many exceptions?

By Sarah Everts

Image: Dan Saelinger

In Brief

• Amino acids, the building blocks of proteins, can adopt forms that, like our right and left hands, are mirror images of each other. When life arose on the earth, it favored so-called left-handed amino acids over right-handed ones to carry out cellular activities.
• For a long time the only exceptions to this pattern were found in bacteria. In recent years, though, more and more examples have been found in higher organisms, including humans.
• Biomedical researchers are studying applications of the exotic amino acids to treat medical conditions, such as schizophrenia, cystic fibrosis and macular degeneration.

Irritate a male platypus during breeding season, and you may end up trapped by its stumpy hind legs, threatened by a set of sharp spurs that are armed with venom. The painful poison hobbles male competitors and is a handy defense against pesky humans and dogs. It is also a somewhat odd concoction, as might be expected from a mammal that is famous for its egg-laying, duck-billed weirdness. Platypus venom contains a class of molecules that biologists once thought did not occur naturally outside the microscopic world of bacteria.

Those molecules are mirror images of the amino acids that cells normally string together to make all of life's proteins, which are vital to proper functioning. The mirror images are composed of the same atoms that make up the 20 or so standard amino acids in biology's tool kit, and the atoms are attached to one another in the same order. Yet the orientation of the attachments diverges slightly, resulting in structures that differ from classic amino acids in much the way a right hand differs from a left hand. The two forms are not, however, interchangeable in biological reactions. Indeed, classic amino acids are now referred to as left-handed, and their mirror images are said to be right-handed.

This article was originally published with the title Mirror Molecules.

Source: http://rss.sciam.com/click.phdo?i=c4749bc94965186880a2caa925e07f94

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