Proteins are made of amino acids, which are thought to have been around long before life emerged:
In living organisms today, amino acids combine with RNA to make a protein. But this translation process requires a set of protein enzymes that, paradoxically, are made by protein synthesis. It becomes a chicken or egg problem: How was a protein made without a protein?
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First, the team took an amino acid and “activated it” — basically removing a water molecule, which made it reactive and able to form a bond with other molecules. But the activated amino acid wouldn’t directly bind to RNA in this form. The team needed to find a helper molecule that would aid the amino acid in binding to RNA.
Powner and his colleagues decided to experiment with a class of compounds called thiols, or molecules with a sulfur attached to a carbon. These molecules are better known for their role in energy production and regulation in cells than for protein synthesis, but the team previously found they are fairly easy to make under basic conditions that would have existed on a baby Earth.
When the thiol was introduced, the team found it first reacted with the activated amino acid in water and then slowly transferred that amino acid to RNA. More of these compounds combine and form proteins in cells.
The binding “was very unexpected [and] wasn’t what we set out to achieve,” Powner said. He said this mechanism essentially solves how to initiate protein synthesis without another protein.
“In a scenario where you have amino acids, where you have RNA molecules, if you have thiols — sulfur molecules — this is, I think, almost inevitable that this kind of process can happen,” Powner said.