From Rutgers University via Forbes: “A Tiny Protein Like This May Have Kick-Started Life On Earth”

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From Rutgers University

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Forbes

Aug 31, 2018
Fiona McMillan

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Ambidoxin is a synthetic small protein that wraps around a metal core composed of iron and sulfur. Vikas Nanda/Rutgers University-New Brunswick

Researchers have reverse engineered a simple protein that may have helped kick start life on Earth.

Their findings, published in the Journal of the American Chemical Society, provide strong new evidence that simple protein catalysts could have contributed to the development of life.

A few decades ago, a chemist named Günter Wächtershäuser put forward a theory that life most likely began on volcanic rocks in the ocean that were rich in iron, sulfur and a variety of other minerals and elements useful for the kind of chemistry needed for simple life forms to emerge. He and others went on to surmise that this process would have been helped along by peptides — which are short proteins — that would have been capable of functioning as catalysts.

A catalyst is anything that can speed up or increase the likelihood of a chemical reaction. Protein catalysts, or enzymes, are able to achieve this by bringing the reactants together in close proximity, and sometimes by also bringing other factors into the mix that help the reaction along, such as a metal ion, a water molecule, or some other type of molecule that gets things moving. In this way, enzymes are like really good party hosts.

Of course, modern enzymes are often big bulky things comprising hundreds of amino acids. There are 20 amino acids to choose from, so countless combinations are possible. These big, complex enzymes are able fold into a stunning variety of elaborate shapes, enabling them to capture and hold reactants, and carry out reactions. They’re absolutely critical to the function of both simple and complex cellular life; we literally couldn’t live without them.

However, such complex molecules took billions of years to evolve. Wächtershäuser and others have proposed that the earliest peptides would have had much simpler structures — perhaps just 10 or 20 amino acids — with just enough chemical complexity to enable them to carry out basic primordial chemistry.

Yet exactly what such peptides may have looked like has been a mystery.

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Underwater sulfur chimneys at Northwest Eifuku volcano. Life may have begun on volcanic underwater rocks like these.Credit: Pacific Ring of Fire 2004 Expedition. NOAA Office of Ocean Exploration; Dr. Bob Embley, NOAA PMEL, Chief Scientist; Public domain image

Now Vikas Nanda and his colleagues at Rutgers University have used computer modeling to find out just how simple a peptide can get while still retaining the ability to function as a catalyst.

In so doing, they have designed a peptide only 12 amino acids long that is able to wrap around a cluster of iron and sulfur atoms, which closely resemble iron-sulfur clusters that would have been found in ancient oceans.

Interestingly, the peptide, which they named ambidoxin, doesn’t need the full variety of 20 amino acids available to modern proteins — it only requires two types of amino acid. Given its simplicity, the researchers suggest such a structure could have evolved spontaneously under the right conditions.

Importantly, ambidoxin is able to carry out simple oxidation-reduction chemistry, also known as redox catalysis. Essentially it is able to be charged and discharged without falling apart, effectively enabling it to shuttle electrons from one place to another.

“Modern proteins called ferredoxins do this, shuttling electrons around the cell to promote metabolism,” says senior author Paul G. Falkowski, who leads Rutgers’ Environmental Biophysics and Molecular Ecology Laboratory.

“A primordial peptide like the one we studied may have served a similar function in the origins of life,” he says.

By shuttling electrons around, ambidoxin (or something like it) may have contributed to early metabolic cycles, and could have served as a precursor to longer, more complex enzymes.

See the full article here .


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