August 5, 2003

Purdue scientists discover why we’re all lefties deep down

WEST LAFAYETTE, Ind. – It may be a right-handed world, but recent Purdue University research indicates that the first building blocks of life were lefties – and suggests why, on a molecular level, all living things remain southpaws to this day.

Download graphic - caption below

In findings that may shed light on the earliest days of evolutionary history, R. Graham Cooks and a team of Purdue chemists have reported experiments that suggest why all 20 of the amino acids that comprise living things exhibit "left-handed chirality," which refers to the direction these basic biological molecules twist–and how a single amino acid might be the reason.

Amino acids can be oriented either to the left or the right and possess the same chemical properties regardless of their chirality. But somewhere along the line, living things evolved using only amino acids of the left-handed variety. Scientists have puzzled over the reason for many years, but Cooks’ group seems to have found the answer: A single amino acid called serine set the standard eons ago, forcing all other biological molecules to follow suit.

"We believe that serine was the first biological molecule to make a chiral choice, possibly one of the root steps in chemical evolution itself," said Cooks, Henry Bohn Hass Distinguished Professor of Analytical Chemistry in Purdue’s School of Science. "Left-handed serine was able to form clusters with strong bonds, and left-handed serine clusters are able to link to other left-handed amino acids. So once serine took the left fork in the road, only the lefties in the primordial soup got to partner up for the dance of life."

Proteins – larger biomolecules – followed the lead taken by serine, Cooks said. The study also suggests that the chirality of other biomolecules, such as sugars, was determined by serine as well.

Cooks’ research, co-authored with Sergio Nanita and Zoltan Takats, doctoral students who are members of Cooks' research group, appears as the cover article in the current issue of the German journal Angewandte Chemie, considered a leading chemistry publication.

Just as books with thousands of words can be written using only 26 letters, the thousands of proteins that form all living things are built out of different combinations of 20 amino acids, which are among the simplest of biological molecules. All molecules exhibit variou