A part of a protein that may be key to identifying planets on the edge of supporting life has been discovered by a group of Rutgers researchers trying to identify the earliest origins of metabolism, the set of basic chemical events that originally powered life on Earth.
The research, published in Science Advances, has important implications for the search for extraterrestrial life because it provides researchers with a new clue to the search, said Vikas Nanda, a researcher at the Center for Advanced Biotechnology and Medicine (CABM) at Rutgers.
Based on laboratory studies, Rutgers scientists say that one of the most likely chemical candidates to start life was a simple peptide with two nickel atoms that they call “Nickelback,” not because it has anything to do with a Canadian rock band, but because that it has nitrogen in its backbone. atoms connect two critical nickel atoms. A peptide is a component of a protein made up of several basic building blocks known as amino acids.
“Scientists believe that sometime between 3.5 and 3.8 billion years ago, there was a tipping point, something that started the change from prebiotic chemistry — molecules before life — to living biological systems,” Nanda said. “We believe the change was triggered by several small precursor proteins that performed key steps in an ancient metabolic reaction. And we think we’ve found one of these ‘pioneer peptides’.”
The scientists conducting the study are part of a Rutgers-led team called Evolution of Nanomachines in Geospheres and Microbial Ancestors (ENIGMA), which is part of the Astrobiology program at NASA. Scientists are trying to understand how proteins evolved to become the predominant catalyst for life on Earth.
When NASA scientists search the universe with telescopes and probes for signs of past, present or emerging life, they look for specific “biological signatures” known to be harbingers of life. Peptides like Nickelback could become the latest biological signature used by NASA to detect planets on the verge of producing life, Nanda said.
The original inciting chemical, the researchers reasoned, would have to be simple enough to assemble spontaneously in the prebiotic soup. But it would have to be chemically active enough to have the potential to extract energy from the environment and drive a biochemical process.
To do so, the researchers adopted a “reductionist” approach: They began by examining existing contemporary proteins known to be associated with metabolic processes. They knew that proteins were too complex to appear early, so they reduced them to their basic structure.
After a series of experiments, the researchers concluded that Nickelback was the best candidate. The peptide consists of 13 amino acids and binds two nickel ions.
Nickel, they reasoned, was an abundant metal in the early oceans. When the nickel atoms are attached to the peptide, they become effective catalysts, attracting additional protons and electrons and producing hydrogen gas. Hydrogen, the researchers reasoned, was also more abundant on early Earth and would have been a critical source of energy for metabolism.
“This is important because while there are many theories about the origin of life, there are very few actual laboratory tests of these ideas,” Nanda said. “This work shows that not only are simple protein metabolic enzymes possible, but that they are very stable and very active – making them a plausible starting point for life.”
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