“ What is life then? It is a physical process that rides on matter like a strange, slow wave. It is a controlled and artistic chaos, a set of chemical reactions so overwhelmingly complex that more than eighty million years ago produced the mammalian brain that now, in human form, writes love letters and uses silicon computers to calculate the temperature of matter. at the origin of the universe ”. In this poetic way they described Lynn Margulis and her son Dorian Sagan in their book ‘What is life?’ that which defines the object of study of biology and whose secrets we have not yet been able to unravel.
We are barely able to define life (it is a controversial concept, especially in ‘intermediate’ forms such as viruses) and even less to clarify its origin, about which there are various theories and unresolved questions.
One of the questions refers to the origin of proteins, the fundamental building blocks that make up the structure of living organisms. To understand the significance of this question we must clarify some basic biochemistry concepts. Proteins are made up of amino acids, a type of organic molecule. The union of two or more amino acids originates peptides , and we call peptides proteins when they have a high molecular weight and, according to the author’s criteria, are formed by a chain of more than 50-100 amino acids with a certain three-dimensional structure.
It was before chicken or the egg?
The problem with its origin is that the reaction necessary for the peptides to form from amino acids requires enzymes, which are also proteins. “We are faced with the classic dilemma: who was first, the chicken or the egg?” Explains Matthew Powner, a researcher at University College London. Powner and his team just published an article in the journal Nature in which they demonstrate how peptides can take a kind of shortcut and form without the need for amino acids.
In their work they reveal that the precursors of amino acids, called aminonitriles, under certain conditions could be converted directly into amino acids taking advantage of their own reactivity and with the help of other molecules that would also be present in that primal environment of the Earth.
“Many researchers have tried to understand how the first peptides that were the basis of life were formed, but most of the research has focused on amino acids, overlooking the reactivity of their precursors,” explained Powner.
Under normal conditions, aminonitriles require very extreme pH conditions – strongly acidic or alkaline – to form amino acids which, in turn, require a lot of energy to bind and form peptides. Well, the British team found a way to skip these two steps, obtaining, directly, peptides from aminonitriles.
Highly reactive molecules
The researchers found that amino nitriles, due to their innate reactivity, are able to form peptide bonds in water much more easily than amino acids. In the article published in Nature , a sequence of simple reactions that combine hydrogen sulfide with aminonitriles and ferricyanide is described, leading to the formation of peptides.
“Controlled synthesis, in response to environmental or internal stimuli, is an essential part of metabolic regulation, so we think that peptide synthesis could have been part of a natural cycle that took place very early in life. “said Pierre Canavelli, the first author of the article.
Another fact that supports this theory is that the molecules used to experimentally obtain this chain of reactions must have been present in that primitive Earth, since they are compounds that would be released during the emissions of gases resulting from the volcanic activity of that time.
Synthetic chemistry applications
In addition to helping us better understand the processes that gave rise to life, these findings will also be useful on an industrial level, as the formation of amide bonds is essential in the manufacture of many commercially important synthetic materials and pharmaceuticals. This method could lower costs by not needing many of the reagents currently used.
The team of researchers is now analyzing the functional properties of the peptides they have synthesized, and they hope the results will allow them to better understand how they might have contributed to the beginning of life four billion years ago.
