Ancient proteins offer new clues about origins of life on Earth

Amazing stuff! What was going on in the primordial soup between 4.6 and 3.8 billion years ago? Can you guess? 😊

With AI can humans shorten evolution from millions of years to perhaps hours? Time will tell!

"... In the lab, the researchers mimicked primordial protein synthesis of 4 billion years ago by using an alternative set of amino acids that were highly abundant before life arose on Earth.

They found ancient organic compounds integrated the amino acids best suited for protein folding into their biochemistry. In other words, life thrived on Earth not just because some amino acids were available and easy to make in ancient habitats but because some of them were especially good at helping proteins adopt specific shapes to perform crucial functions. ...
Even though the primordial Earth had hundreds of amino acids, all living things use the same 20 of these compounds. Fried calls those compounds "canonical." But science has struggled to pinpoint what's so special—if anything—about those 20 amino acids. ...
Scientists have spotted amino acids in asteroids far from Earth, suggesting those compounds are ubiquitous in other corners of the universe. ..."

From the abstract:

"Whereas modern proteins rely on a quasi-universal repertoire of 20 canonical amino acids (AAs), numerous lines of evidence suggest that ancient proteins relied on a limited alphabet of 10 “early” AAs and that the 10 “late” AAs were products of biosynthetic pathways. However, many nonproteinogenic AAs were also prebiotically available, which begs two fundamental questions: Why do we have the current modern amino acid alphabet and would proteins be able to fold into globular structures as well if different amino acids comprised the genetic code? Here, we experimentally evaluate the solubility and secondary structure propensities of several prebiotically relevant amino acids in the context of synthetic combinatorial 25-mer peptide libraries. The most prebiotically abundant linear aliphatic and basic residues were incorporated along with or in place of other early amino acids to explore these alternative sequence spaces. The results show that foldability was likely a critical factor in the selection of the canonical alphabet. Unbranched aliphatic amino acids were purged from the proteinogenic alphabet despite their high prebiotic abundance because they generate polypeptides that are oversolubilized and have low packing efficiency. Surprisingly, we find that the inclusion of a short-chain basic amino acid also decreases polypeptides’ secondary structure potential, for which we suggest a biophysical model. Our results support the view that, despite lacking basic residues, the early canonical alphabet was remarkably adaptive at supporting protein folding and explain why basic residues were only incorporated at a later stage of protein evolution."

Ancient proteins offer new clues about origins of life on Earth | Hub In early Earth simulation co-led by researchers at Johns Hopkins, scientists gain insights into how amino acids shaped the genetic code of ancient microorganisms

Early Selection of the Amino Acid Alphabet Was Adaptively Shaped by Biophysical Constraints of Foldability (no public access, here is the link to the preprint and PDF)