Direct evidence of 'key ingredient' for first life on Earth identified

The first direct experimental evidence showing the "key ingredient" at the dawn of life on Earth has been discovered by scientists.

Researchers have found how proteins developed the ability to accelerate the chemical reaction needed to synthesise proteins – allowing life to arise on Earth.

Charles Carter, lead author of the study published in the Journal of Biological Chemistry, looked at two major superfamilies of enzymes. He and his team from the UNC School of Medicine found a single ancient gene likely used its two opposite strands of DNA, both of which activated amino acids.

He said: "The peptide made from one strand activated those amino acids needed for the insides of proteins, and the peptide made from the other strand activated those amino acids needed for the outsides of proteins."

How life began on Earth is not known. Scientists think there were simply tiny catalysts that probably evolved the ability to speed up and synchronise the reactions needed for life to evolve. What these catalysts were and how they appeared at the same time is not known.

Speaking to IBTimes UK, Carter said: "We're trying to run the clock backwards from the contemporary modern enzymes to something that by consensus evolutionary thinking must have been part of the ancestral gene.

"I've localised this in the first 500 million years after the Earth cooled to the point there was liquid water. This is kind of an intellectual desert. Outside of this work we have no way to do experiments that tell us what might have happened in that period of time. In my mind that period of time covered the period during which the most dramatic inventions that nature ever made were made."

The key obstacle to the formation of life is the reaction between combines amino acids with adenosine triphosphate, or ATP (which transfers chemical energy within cells). This combination allows proteins to assemble spontaneously.

The researchers devised experiments to take apart synthetases – which speed up this reaction – to show the necessary catalytic activity derives from parts of the enzymes all members of synthetase share – the ability to bind to ATP.

Carter dubbed these enzyme fragments protozymes. Findings showed enzymatic activity focuses on the activation reaction with ATP, meaning the protozymes were able to form tight complexes with structures during the transitions that take place during the chemical reactions that form proteins. This, he said, would be necessary during catalysis – and therefore the creation of the first life on Earth.

The team then conducted experiments to show designer protozymes exhibit the same activity as those Carter's research had identified.

He said: "We discovered that nature solved the problem of activating amino acids destined to be inside (class I) folded proteins and outside (class II) folded proteins by evolving a single gene to do both jobs. Moreover, the protozymes managed to do this in a most unusual way: by relying on two entirely different interpretations of the same genetic information."

Carter said this finding has opened up the field somewhat in the search for how life on Earth began.

He said: "We now have more information about how amino acids eventually evolved into complex molecules necessary to create life as we know it. But perhaps more importantly, we've been able to provide a new set of tools that will enable others to approach questions about the origin of life in ways that are scientifically sound and productive."

Carter said he is "optimistic" we will discover exactly how life on Earth began. He said: "I think the human species is curious enough and has developed the necessary tools to give an affirmative answer to that question. I think we're still quite a way away; there are many many unanswered questions."

He said the findings provided a "set of tools" with which scientists can now conduct experiments, allowing them to frame questions as to how they came to be. Carter said: "Where did these protozymes actually come from? There must have bene a blueprint for them.

"Where did that blueprint come from? I think the fact that these protozymes are catalytically accessible, that we can actually do experiments with them, that we can begin to work backwards to even simpler ancestors.

"Life comes from very important coincidences in the laws of physics. From my perspective this is the first time we've been able to think about doing that kind of experiment that is closely related to a question of the start of life on Earth."