Researchers at Rutgers and Rice Universities have shed some light on the mystery of how life on Earth got started. After studying proteins that are key to metabolism in modern cells, the team reverse engineered a simplified protein that may have been responsible for kickstarting the process in ancient times. And to prove the idea, they then implanted it into living bacteria and found that it works just fine.
The protein in question belongs to a group called ferredoxins. These proteins act like biological capacitors, using clusters of iron and sulfur to accept electrons from one molecule and pass them onto other molecules. This makes them vital to the process of metabolism in bacteria, plants and animals.
Modern ferredoxins come in an array of complex forms, but it's believed that all of these would have arisen from a much simpler version, in the distant past. In an earlier study, the Rutger researchers designed a small, synthetic ferredoxin that could be similar to the evolutionary building blocks that life used billions of years ago.
For the new study, the Rutgers scientists teamed up with researchers at Rice to put these synthetic proteins to the test – namely, by seeing if they do their expected job in a lifeform. The researchers edited the genome of the bacteria E. coli to remove the gene it naturally uses to produce ferredoxins, and then spliced in a gene that encodes for the engineered, more simple version of the protein.
The team created several different variations, and found that they generally did the job. Although the E. coli colonies grew more slowly than usual, they did survive, with the proteins functioning well enough at transferring electrons between molecules.
The study has many implications. For one, it improves our understanding of the evolution of early life on Earth, and possibly that of extraterrestrials.
"We are closer to understanding the inner workings of the ancient cell that was the ancestor of all life on earth – and, therefore, to understanding how life arose in the first place, and the pathways life might have taken on other worlds," says Andrew Mutter, lead author of the study.
The breakthrough is also important for synthetic biology. Understanding how metabolism works and how it can be exploited could allow scientists to program microbes for all sorts of uses, such as energy storage, biofuel production or even fighting viruses.
"These proteins channel electricity as part of a cell's internal circuitry," says Vikas Nanda, co-author of the study. "The ferredoxins that appear in modern life are complex – but we've created a stripped-down version that still supports life. Future experiments could build on this simple version for possible industrial applications."
The research was published in the journal Proceedings of the national Academy of Sciences.
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