The question of how life first emerged here on Earth is a mystery that continues to elude scientists. Despite everything that scientists have learned from the fossil record and geological history, it is still not known how organic life emerged from inorganic elements (a process known as abiogenesis) billions of years ago.
One of the more daunting aspects of the mystery has to do with peptides and enzymes, which fall into something of a "chicken and egg" situation.
Addressing this, a team of researchers from the University College London (UCL) recently conducted a study that effectively demonstrated that peptides could have formed in conditions analogus to primordial Earth.
The study which details their findings was recently published in the scientific journal Nature. The research team was led by Dr. Matthew Powner, a Reader of Organic Chemistry with UCL's Department of Chemistry, and included Pierre Canavelli and Dr. Saidul Islam – both of whom are researchers with UCL's Organic and Biological Chemistry Section.
As Powner explained the purpose of their study in a recent interview with UCL News:
"Peptides, which are chains of amino acids, are an absolutely essential element of all life on Earth. They form the fabric of proteins, which serve as catalysts for biological processes, but they themselves require enzymes to control their formation from amino acids. So we've had a classic chicken-and-egg problem – how were the first enzymes made?"
As they indicate in their study, considerable research in the past has been dedicated to finding out how peptides first formed and allowed for the emergence of life. However, all previous research has focused on amino acids, rather than the reactivity of their chemical precursors (known as aminonitriles).
Whereas aminonitriles require harsh conditions to form amino acids (typically strongly acidic or alkaline), amino acids need to be recharged with energy to form peptides. However, the researchers found a way to bypass both of these steps by demonstrating that peptides could be made directly from energy-rich aminonitriles.
Their method took advantage of the built-in reactivity of aminonitriles with the other molecules that were a part of Earth's primordial environment. The process consisted of combining hydrogen sulfide with aminonitriles and the chemical substrate ferricyanide ([Fe(CN)6]3?) in water, which yielded peptides.
What this demonstrated was that aminonitriles are capable of achieving peptide bond formation in water all on their own, and with greater ease than amino acids.
In addition, it showed that this could take place amid conditions and chemicals that are outgassed during volcanic eruptions and which were likely present on Earth billions of years ago. Said Pierre Canavelli, the first author of the study:
"Controlled synthesis, in response to environmental or internal stimuli, is an essential element of metabolic regulation, so we think that peptide synthesis could have been part of a natural cycle that took place in the very early evolution of life."
"This is the first time that peptides have been convincingly shown to form without using amino acids in water, using relatively gentle conditions likely to be available on the primitive Earth," added co-author Dr Saidul Islam.
These findings could have significant implications for the study of abiogenesis, as well as the search for life on extrasolar planets. They may also be useful to the field of synthetic chemistry since amide bond formation is essential to the manufacture of synthetic materials, bioactive.
Compared to conventional chemical processes that are used commercially, this new method is more efficient and much more cost-effective.
Looking ahead, the research team is looking to further their studies by finding other ways in which aminonitriles can lead to peptides. They are also currently investigating the functional properties of peptides that their experiment produced in the hopes of better understanding how they could have helped trigger the formation of life on Earth ca. 4 billion years ago.
After many generations of trying (and failing) to recreate the building blocks of life, could it be that scientists have simply been going about it backwards? And does this mean that organic technology could be right around the corner?
Only time will tell…