Carbon might be the backbone of organic chemistry, but life on Earth wouldn't be what it is today if it weren't for another critical member of the periodic table – phosphorus.
Transforming run of the mill hydrocarbons into the kinds of molecules that include this important element is a giant evolutionary leap, chemically speaking. But now scientists think they know how such a vital step was accomplished.
Researchers from The Scripps Research Institute in California have identified a molecule capable of performing phosphorylation in water, making it a solid candidate for what has until now been a missing link in the chain from lifeless soup to evolving cells.
In the classic chicken and egg conundrum of biology's origins, debate continues to rage over which process kicked off others in order to get to life. Was RNA was followed by protein structures? Did metabolism spark the whole shebang? And what about the lipids?
No matter what school of abiogenesis you hail from, the production of these various classes of organic molecules requires a process called phosphorylation – getting a group of three oxygens and a phosphorus to attach to other molecules.
Nobody has provided strong evidence in support of any particular agent that might have been responsible for making this happen to prebiotic compounds. Until now.
"We suggest a phosphorylation chemistry that could have given rise, all in the same place, to oligonucleotides, oligopeptides, and the cell-like structures to enclose them," says researcher Ramanarayanan Krishnamurthy.
Enter diamidophosphate (DAP).
Combined with imidazole acting as a catalyst, DAP could have bridged the critical gap from early compounds such as uridine and cytidine. That might not seem overly exciting, but phosphorylating nucleosides like these is a crucial step on the road to building the chains of RNA that could serve as the first primitive genes.
Some DAP in room-temperature water also managed to phosphorylate amino acids, as well as assist in their linking into short protein chains.
Even better than that, the researchers demonstrated the same agent could also marry phosphoryl groups with glycerol and fatty acids, producing the kinds of phospholipids that line up into cell membranes.
"With DAP and water and these mild conditions, you can get these three important classes of pre-biological molecules to come together and be transformed, creating the opportunity for them to interact together," says Krishnamurthy.
The diagram below gives you some idea of just how all-singing, all dancing this fancy compound is.
This isn't proof positive of DAP's role in the origins of biology, of course. For one thing, it's yet to be demonstrated that diamidophosphate was present in Darwin's 'warm little pond' some 4 point something billion years ago.
But there are some suspicious DAP-like fingerprints left on today's biochemistry.
"DAP phosphorylates via the same phosphorus-nitrogen bond breakage and under the same conditions as protein kinases, which are ubiquitous in present-day life forms," says Krishnamurthy.
"DAP's phosphorylation chemistry also closely resembles what is seen in the reactions at the heart of every cell's metabolic cycle."
The next step will be to work with geochemists to identify a potential non-biological source of DAP, if not find something similar.
For the better part of a century, researchers have hunted for ways non-living chemicals could potentially self-assemble into complex systems based on simple rules.
It's likely that there will always be gaps in our knowledge on the origins of life. DAP helps fill one aching void, at least.
This research was published in Nature Chemistry.