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An experiment in recreating primordial proteins solves a long-standing riddle:

Scientists believe that the very first true proteins materialized from shorter protein segments called peptides. The peptides would have been sticky assemblies of the amino acids that were spontaneously created in the primeval chemical soup; the short peptides would have then bound to one another, over time producing a protein capable of some sort of action. The spontaneous generation of amino acids had already been demonstrated in 1952, in the famous experiment by Miller and Urey, in which they replicated the conditions thought to exist on Earth prior to life and added energy like that which could come from lightning or volcanoes. Showing amino acids could, under the right conditions, form without help from enzymes or any other mechanism in a living organism suggested that amino acids were the "egg" that preceded the enzyme "chicken."

Tawfik, who is in the Institute's Biomolecular Sciences Department, says that is all well and good, "but one vital type of amino acid has been missing from that experiment and every experiment that followed in its wake: amino acids like arginine and lysine that carry a positive electric charge." These amino acids are particularly important to modern proteins, as they interact with DNA and RNA, both of which carry net negative charges. RNA is today presumed to be the original molecule that could both carry information and make copies of itself, so contact with positively-charged amino acids would theoretically be necessary for further steps in the development of living cells to occur.

But there was one positively-charged amino acid that appeared in the Miller-Urey experiments, an amino acid called ornithine that is today found as an intermediate step in arginine production, but is not, itself, used to build proteins. The research team asked: What if ornithine was the missing amino acid in those ancestral proteins? They designed an original experiment to test this hypothesis.

Also at phys.org

Journal Reference:
Liam M. Longo, Dragana Despotović, Orit Weil-Ktorza, et al. Primordial emergence of a nucleic acid-binding protein via phase separation and statistical ornithine-to-arginine conversion [$], Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.2001989117)

Original Submission