Phosphorus compound could have created three crucially vital components
Three at one stroke: A small phosphorus compound could have been the crucial prerequisite for first life on Earth, because this chemical was able to synthesize three major biomolecules: Nucleotides as precursors of RNA and DNA, Peptides as protein precursors and Lipids for the envelope membranes of the first cells. Thus, the molecule called Phosphorodiamidate was possibly the key to the development of the first cells.
A molecule could have helped in the formation of three important life molecules. © Natalia Kollegova / pixabay
One thing is clear: at about 3.5 billion years ago, the first living cells must have appeared on Earth. But where and how this happened is still puzzling. For example, the first RNA and DNA building blocks could have been formed by lightning or brought to Earth by comets. However, how these building blocks became chain-shaped genetic molecules and how the first proteins were formed from amino acids is just as unclear as the formation of the first cell envelopes from lipids.
One of the reasons: All these biomolecules require a special chemical reaction for their formation, the so-called Phosphorylation. However, all of the candidate reactants would only have worked in one of these three basic classes of life molecules, or they would need very specific environmental conditions incompatible with primordial soup.
It is therefore hard to imagine how these very different reaction processes should have taken place in one place to form the first primitive life forms, explains Ramanarayanan Krishnamurthy of the Scripps Research Institute at La Jolla.
It would be much more obvious that there was a molecule in the primordial soup that could phosphorylate all three substance classes. But such an "all-rounder" has been sought in vain.
One molecule - three effects
Now, however, Krishnamurthy and his colleagues may have found just this missing molecule. As they found in experiments, the phosphorus-nitrogen compound phosphorodiamidate (H4N2O2P) can react with a wide range of biomolecule building blocks and assemble them into larger chains. What is needed is only an aqueous solution of the building blocks and the catalyst Imidazole, a simple organic compound that was most likely present in primordial soup.
Phosphorodiamidate is a compound of phosphorus, oxygen and nitrogen. © public domain
For example, if the phosphorodiamidate is added to a solution containing the four nucleotide bases of the RNA, it phosphorylates it and joins it into short RNA chains, the researchers report. The phosphorodiamidate also combines single fatty acids and glycerine to lipids with similar efficiency.
We were surprised to see that even large vesicles with lipid bilayer formed, report Krishnamurthy and his colleagues.
And even with the third important class of molecules of life, the phosphorus compound reacted - with amino acids. In the experiment, it combined the amino acids glycine, aspartic acid and glutamic acid by phosphorylation into short peptide chains.
Obstetrician of first life?
With that, the researchers could finally have discovered the actor which co-created the most important life molecules.
It almost reminds me a little bit of the fairy, who wields her wand in the fairytale Cinderella, turning simple everyday objects into something more complex and interesting, says Krishnamurthy. This phosphorylation agent could then have created both oligonucleotides and oligopeptides and the cell-like structures that included them in one place.
Thus only the phosphorodiamidate would have created the conditions under which the first life could form. Whether phosphorodiamidate was actually present in primeval soup, however, is likely to be difficult to prove after more than 3.5 billion years. But at least the scientists think it is very likely - also because this molecule can work under aqueous conditions and in a wide range of temperatures.
Echo of primordial soup chemistry still in our cells
At least there is some evidence that the necessary building blocks were present for those on the primeval Earth.
Astronomers have discovered evidence for phosphorus-nitrogen compounds in the gas and dust of interstellar space, says Krishnamurthy. It is therefore very plausible that such compounds were also present on the early Earth and played a role in the formation of complex life molecules.
In addition: until today, the phosphorylation of molecules in our cells takes place in a very similar way as by the Phosphorodiamidate - even if the actors are now different.
Thus, phosphorodiamidate phosphorylates by the same breakage of phosphorus-nitrogen bonds and under the same conditions as protein kinases, says Krishnamurthy. And at the heart of each cell's metabolic cycle, chemistry is quite similar to that of phosphorodiamidate.