Imagine a world before life as we know it. A world where organic compounds were just beginning to take shape, and the very building blocks of life were being formed. This is the world that scientists have been working hard to understand by simulating conditions on Earth some 4.6 billion years ago.
Their aim? To unlock a greater understanding of how amino acids brought the first ingredients for life into being. And what they discovered was nothing short of astonishing. Proteins play many vital roles in organisms, and scientists have long known that amino acids are the key components that make up these proteins. But what they wanted to know was why a specific group of 20 'canonical' amino acids is used again and again to build proteins when there are so many more of these amino acids to pick from. Through a reconstruction of primordial protein synthesis, the researchers showed that ancient organic compounds would have favored the amino acids best at folding proteins, tailoring them for specific functions. In other words, a process of evolution or natural selection was underway even at this stage: it wasn't the amino acids that were most readily available that were picked, but the amino acids most suited to a particular job.
"If other amino acids had been selected as part of the core group billions of years ago," noted chemist Stephen Fried, "the very building blocks of life would not have been as efficient at doing that life-building." But what's truly fascinating is that this process of protein folding allowed for evolution to take place even before there was life on Earth! "You could have evolution before you had biology," explains Fried. "You could have natural selection for the chemicals that are useful for life even before there was DNA." The implications of this research go far beyond our own planet. The same amino acids found on Earth can also be found in many other places in the Universe. "Maybe if we found life on a different planet," suggests Fried, "it wouldn't be that different."
As we continue to explore our universe and search for signs of extraterrestrial life, this new understanding of how proteins may have evolved before life itself could prove invaluable. The study has been published in the Journal of the American Chemical Society – an important milestone in our quest to understand how life came into being on Earth and beyond.