Each and every organism present on Earth has amino acids. That’s because all things on Earth are connected through this tree of life with an origin, an organism that was the ancestor of all living things. A new study describes the events that shaped why that ancestor got the amino acids that it did.
To do so, scientists simulated early Earth conditions in the lab. They mimicked primordial protein synthesis of 4 billion years ago by using an alternative set of amino acids that were highly abundant before life arose on Earth.
They discovered that the biochemistry of prehistoric organic compounds included the amino acids most suitable for protein folding. In other words, life evolved on Earth because some amino acids were available and simple to synthesize in prehistoric settings. Some were particularly good at assisting proteins in taking on particular forms to carry out essential activities.
Ancient proteins would not have known how to evolve into everything alive today without specific amino acids.
Stephen Fried, a Johns Hopkins chemist who co-led the research with scientists at Charles University in the Czech Republic, said, “Protein folding allowed 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.”
Throughout its first billion years, Earth’s atmosphere was made up of various gases, including ammonia and carbon dioxide, which combined with intense ultraviolet radiation to create some of the simplest classical amino acids. Others arrived via special delivery by meteorites, which brought a variety of components and completed a set of 10 “early” amino acids that helped life on Earth.
Fried said, “We’re trying to discover what was so special about our canonical amino acids. Were they selected for any particular reason?”
According to scientific estimates, the Earth is 4.6 billion years old, and it took until 3.8 billion years ago for DNA, proteins, and other chemicals to start forming primitive life. The latest research provides fresh hints on the enigma of what transpired in between.
Fried said, “To have evolution in the Darwinian sense, you need to have this 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.”
Amino acids have been found in asteroids distant from Earth, indicating that these substances are common across the universe. Fried believes the new findings may also impact the likelihood of discovering life in space.
Fried said, “The universe seems to love amino acids. Maybe it wouldn’t be that different if we found life on a different planet.”
- Mikhail Makarov, Alma C. Sanchez Rocha et al. Early Selection of the Amino Acid Alphabet Was Adaptively Shaped by Biophysical Constraints of Foldability. The Journal of the American Chemical Society. DOI: 10.1021/jacs.2c12987