Scientists Create Brand New Organism

By Cat Lazaroff

WASHINGTON, DC, January 14, 2003 (ENS) - A group of scientists has created an organism that produces an amino acid that no other living thing has ever used.

All living things use the same 20 amino acids to build all of the proteins that make up all living cells. Now, scientists led by Scripps Research Institute chemistry professor Dr. Peter Schultz have engineered a version of the E. coli bacteria that can produce a 21st amino acid.

The project is designed to help answer some of the basic questions regarding the evolution of life, such as why organisms have not evolved more than 20 of these basic chemical building blocks. The researchers hope to learn whether access to additional amino acids could give organisms an evolutionary advantage.

E. coli

A photomicrograph of Escherichia coli, (Bacillus coli), bacteria. A team of researchers has engineered a new version of this ubiquitous bacteria, one that can produce an unnatural amino acid. (Photo courtesy Centers for Disease Control)
"Why did life settle on 20 amino acids?" said Dr. Ryan Mehl, once a researcher at Scripps and now on the faculty of Franklin & Marshall College in Lancaster, Pennsylvania. "Would more amino acids give you a better organism - one that could more effectively adapt if placed under selective pressure?"

To address this question, Mehl, Schultz and their collaborators added a pathway to an E. coli bacterium that allows it to make the new amino acid - p-aminophenylalanine (pAF) - from simple carbon sources. Analytical techniques showed that pAF was incorporated into proteins just as well as the 20 natural amino acids.

"This allows you to have a totally autonomous organism that you can 'race'in one pot by evolving the new bacterium alongside its ancestors with 20 amino acids," said Christopher Anderson, a researcher at Scripps and another author of the paper.

By racing the organisms - exposing both to selective pressures at the same time and watching their development - the researchers hope to see if the organism with the expanded genetic code has an evolutionary advantage over natural organisms.

A number of scientists have added unnatural amino acids to organisms, but most of these experiments involved eliminating the organism's supply of the natural amino acid and substituting a close relative.

"So, in the end, you still have a 20 amino acid bacterium, but it's using an unnatural amino acid instead of the natural one," Anderson explained.

"What our group really wanted to do is expand the genetic code, not just recode it. To do that, it takes a lot more effort," added Anderson. "You have to come up with some way of specifically denoting how the protein is going to encode this 21st amino acid, because everything else in the genetic code already has a meaning associated with it."

Schultz

Dr. Peter Schultz led the research that created the new version of E. coli. (Photo courtesy Scripps Research Institute)
The scientists managed, though genetic engineering techniques, to create a bacterium that can make the new amino acid by itself, as opposed to being fed the unnatural amino acid from an outside source.

"This bug is self sufficient; it can make, load and incorporate the new amino acid in the emerging protein all on its own," Mehl said. "It's a bona fide unnatural organism now. Essentially, this bacterium can be added to a minimal media [salts and a basic carbon source] and it's able to do the rest."

E. coli is notorious for its ability to reproduce fast, so the researchers took careful steps aimed at preventing the bacteria from escaping the laboratory.

"We crippled the organism's ability to biosynthesize leucine [one of the 20 essential amino acids] to avoid any risk that the organism could propagate outside a controlled lab setting," Anderson said. "Our unnatural organism will always live in the lab. We have no intention of putting it out in the wild or in commercial products where it could 'get out'."

The research team next hopes to develop organisms that can produce unnatural amino acids that are more useful to medicine and industry.

"We are now focusing on more 'useful' unnatural amino acids such as ketone and PEG containing amino acids," Anderson said.

PEG stands for polyethylene glycol, a polymer that can be connected to proteins used in medicines to enhance their therapeutic value.

"I don't think it is at all unrealistic to imagine that in the not too distant future there will be a transgenic goat that can biosynthesize a PEG amino acid and incorporate it into therapeutic proteins secreted into the animal's milk," Anderson concluded. "We are just beginning to look at the applications, but we have many projects in the works."

The team's findings are scheduled to appear in the January 29 print edition of the "Journal of the American Chemical Society." The article was published January 4 on the journal's website.

For more information on Scripps research regarding encoding for unnatural amino acids, visit: http://schultz.scripps.edu/Research/UnnaturalAAIncorporation/research.html