How did life arise on Earth? Researchers have found among the first and perhaps only hard evidence that simple protein catalysts – essential for cells, the building blocks of life, to function – may have existed when life began.
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Extremely fascinating, it contains a heterochiral mix of amino acids. This strongly indicates you don’t actually need homochirality to get a functional biopolymer.
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While this seems like a a very thorough paper (I skimmed through the 40+ pages of supplemental info since I don’t have access to JACS unfortunately) and quite a feat, I feel like the ScienceDaily article exaggerates the significance to OoL research.
Essentially, researchers did a lot of work to find and build a 12-amino acid polypeptide that had robust electron transfer activity. It was impressive because it was short, used only two amino acids, and is heterochiral as @Rumraket pointed out.
What I don’t see, is any correlation to any actual polypeptide known to exist 4 billion years ago. This was, as far as I can tell, a proof of concept to help see how simple polypeptides/proteins might be to have function needed for life to exist. The JACS abstract is, naturally, a better description:
Ambidoxin is a designed, minimal dodecapeptide consisting of alternating L and D amino acids that binds a 4Fe–4S cluster through ligand–metal interactions and an extensive network of second-shell hydrogen bonds. The peptide can withstand hundreds of oxidation–reduction cycles at room temperature. Ambidoxin suggests how simple, prebiotic peptides may have achieved robust redox catalysis on the early Earth.
I was wondering why they didn’t cite Eck and Dayhoff’s 1966 article on Ferredoxin which to my knowledge is the first where it is suggested 4Fe–4S cluster proteins trace to the origin of life:
Eck RV, Dayhoff MO. Evolution of the structure of ferredoxin based on living
relics of primitive amino Acid sequences. Science. 1966 Apr 15;152(3720):363-6.
PubMed PMID: 17775169.
Abstract
The structure of present-day ferredoxin, with its simple, inorganic active site and its functions basic to photon-energy utilization, suggests the incorporation of its prototype into metabolism very early during biochemical evolution, even before complex proteins and the complete modern genetic code existed. The information in the amino acid sequence of ferredoxin enables us to propose a detailed reconstruction of its evolutionary history. Ferredoxin has evolved by doubling a shorter protein, which may have contained only eight of the simplest amino acids. This shorter ancestor in turn developed from a repeating sequence of the amino acids alanine, aspartic acid or proline, serine, and glycine. We explain the persistence of living relics of this primordial structure by invoking a conservative principle in evolutionary biochemistry: The processes of natural selection severely inhibit any change a well-adapted system on which several other essential components depend.