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| Researchers have designed a synthetic small protein that wraps around a metal core composed of iron and sulfur. This protein can be repeatedly charged and discharged, allowing it to shuttle electrons within a cell. Such peptides may have existed at the dawn of life, moving electrons in early metabolic cycles. Image: Vikas Nanda Source: Rutgers Today |
Researchers at Rutgers University have found perhaps the only hard evidence that simple protein catalysts may have existed when life began.
It has long been postulated that life may have begun on iron and sulphur-containing rocks in sea water and that these metals, bound to short peptide chains could have acted as catalysts for simple metabolic processes, long before RNA, DNA and bigger, more complex proteins evolved.
The team used computer modelling to design a short, 12-amino acid peptide for testing. This one had just two different amino acid from the 20 of which larger proteins are made. Being short and simple, it could easily have arisen spontaneously and the metal cluster at the heart of the catalyst are similar to those found in in the oceans on early Earth when life arose.
Most importantly, the molecule can charge and discharge electrons repeatedly without degrading in the process. This function is carried out in modern cells by proteins known as ferredoxins.
Abstract
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.
Kim, J. D., Pike, D. H., Tyryshkin, A. M., Swapna, G. V. T., Raanan, H., Montelione, G. T., Nanda, V., Falkowski, P. G. (2018).
Minimal heterochiral de novo designed 4Fe-4S binding peptide capable of robust electron transfer.
J. Am. Chem. Soc., Article ASAP DOI: 10.1021/jacs.8b07553
Copyright © 2018 American Chemical Society.
Reprinted with kind permission.
No doubt, creationists will get excited over the fact that this catalyst was designed by scientists with the age of computer technology. What they won't recognise is that there was no 'magic' involved in actually assembling the short, 12-amino acid chain from just two different amino acids with the sulphur/iron cluster in the centre. This was just basic chemistry from chemicals that were there at this stage in Earth's history and at the beginning of life.
This isn't abiogenesis in the sense that it wasn't an early, free-living, self-replicating system enclosed in a membrane, but it shows how just such a system could itself be the result of an evolutionary process from very simple precursors which could easily have arisen spontaneously.
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