How did life begin on our planet? This is the main question that astrobiology tries to solve, a science that investigates the origins of our existence in order to also try to understand if life as we know it on other planets is possible.
Now, a team of scientists from New Jersey State University (USA) has identified a possible candidate to be the first protein on Earth, a molecule that would also have the capacity to perform catalysis – accelerate chemical reactions – a fundamental process for the cells. It is not, of course, a complex protein like those that are part of our body, which usually consist of between hundreds and thousands of amino acids , since these are the result of millions of years of evolution. It is estimated that the first proteins on Earth would be much simpler, made up of a maximum of ten to twenty amino acids.
It was in the late 1980s that chemist Günter Wächtershäuser theorized that life must have started in the ocean, specifically in rocks containing iron and sulfur. Wächtershäuser and other scientists predicted that the first proteins would have bound to these metals to serve as catalysts for the chemical reactions that produce life.
This is the primordial peptide
To ‘hunt down’ the possible first peptide – short chain protein – on our planet, the team of scientists used a computer simulation and developed a small 12 amino acid peptide that they then tested in the laboratory. It is a molecule that contains only two types of amino acids – compared to the approximately twenty that current proteins contain – it is very short and could have arisen spontaneously on primitive Earth, if the right conditions were given. In addition, in the nucleus of this peptide there is a cluster of metals that resembles the structure and chemistry of iron and sulfur that were abundant in the oceans at that time.
Another of the most relevant characteristics of this primordial protein is that it is capable of being repeatedly charged and discharged, which allows it to transport electrons within a cell. It is a very important capacity if we think that this small molecule would be the basis of the chemical reactions that began to draw life.
“Today’s proteins known as ferredoxins do just this: they transport electrons around the cell to promote metabolism,” explains Professor Paul G. Falkowski, one of the authors. “A primordial peptide like this would have had a similar function in the origins of life.” Those peptides could have acted early in life by moving electrons in early metabolic cycles.
Falkowski is also the principal investigator of a project funded by NASA called ENIGMA, whose main objective is precisely to know how protein catalysis evolved in the beginning of life. With the help of computer simulations, the researchers have already dissected almost 10,000 proteins and in January 2018 they published a work in which they described what they call ‘The LEGOS of life ‘: these are four chemical structures that can stack and form like this all the proteins that make up the interior of all living organisms.
The small primordial peptide now identified could be the precursor to these LEGOS of life, and the next step will be to simulate the processes by which the first peptides would have articulated the chemistry of life in their origins.
The work has been published in the Journal of the American Chemical Society .
Reference: Kim et al. 2018. Minimal Heterochiral de Novo Designed 4Fe – 4S Binding Peptide Capable of Robust Electron Transfer. Journal of the American Chemical Society. DOI: 10.1021 / jacs.8b07553
