Elaborating how amino acids shaped the genetic code of ancient microbes

Researchers discovered that without specific amino acids, ancient proteins would not have identified how to evolve into anything alive on the planet today, including plants, animals, and humans, by mimicking early Earth conditions in the lab.

The observations, which describe how amino acids sculpted the genetic code of ancient microbes, help to explain how life began on Earth.

You see the same amino acids in every organism, from humans to bacteria to archaea, and that’s because all things on Earth are connected through this tree of life that has an origin, an organism that was the ancestor to all living things. We're describing the events that shaped why that ancestor got the amino acids that it did.”

Stephen Fried, Chemist, Johns Hopkins University

Stephen Fried co-led the study with researchers at Charles University in the Czech Republic.

The observations were published in the Journal of the American Chemical Society.

The investigators recreated primordial protein synthesis from four billion years ago in the lab by using an alternative set of amino acids that were prevalent before life on Earth arose.

They discovered that ancient organic compounds incorporated the best amino acids for protein folding into their biochemistry. In other words, life flourished on Earth not only because some amino acids were abundant and easy to produce in ancient habitats but also because some of them were particularly effective at assisting proteins in adopting specific shapes to perform important functions.

Protein folding was basically allowing us to do evolution before there was even life on our planet. You could have evolution before you had biology, you could have natural selection for the chemicals that are useful for life even before there was DNA.”

Stephen Fried, Chemist, Johns Hopkins University

Despite the fact that there were hundreds of amino acids on the primordial Earth, all living things use the same 20 of these compounds. Fried refers to these compounds as “canonical.” However, scientists have been unable to determine what makes those 20 amino acids so unique, if anything at all.

During the first billion years of Earth’s existence, the atmosphere was made up of a variety of gases, such as ammonia and carbon dioxide, which interacted with high levels of ultraviolet radiation to produce some of the simpler canonical amino acids. Others arrived via meteorites, which brought a mixed bag of ingredients that assisted life on Earth in completing a set of 10 “early” amino acids.

Fried’s group is attempting to answer the question of how the rest came to be with the new research, especially since those space rocks brought much more than “modern” amino acids.

Fried adds, “We're trying to find out what was so special about our canonical amino acids. Were they selected for any particular reason?”

According to researchers, the Earth is 4.6 billion years old, and DNA, proteins, and other molecules did not begin to form simple organisms until 3.8 billion years ago. The new research sheds new light on the mystery of what happened in the interim.

To have evolution in the Darwinian sense, you need to have this whole sophisticated way of turning genetic molecules like DNA and RNA into proteins. But replicating DNA also requires proteins, so we have a chicken-and-egg problem. Our research shows that nature could have selected for building blocks with useful properties before Darwinian evolution.”

Stephen Fried, Chemist, Johns Hopkins University

Researchers have discovered amino acids in asteroids far from Earth, implying that these compounds are common in other parts of the universe. That is why Fried believes the new research could have implications for the discovery of life beyond Earth.

“The universe seems to love amino acids. Maybe if we found life on a different planet, it wouldn't be that different,” Fried concludes.