A team of Rutgers scientists, focused on uncovering the origins of metabolism that fueled life on Earth, has discovered a protein fragment that could assist in the identification of planets that may be capable of supporting life. Published in Science Advances, the study has significant implications in the search for extraterrestrial life by providing researchers with a new clue to detect such planets. The protein fragment, dubbed "Nickelback" by the Rutgers scientists, is a simple peptide consisting of two nickel atoms bound by nitrogen atoms in its backbone. While unrelated to the Canadian rock band, this discovery is a promising candidate for the chemical that could have initiated life on Earth.
"Scientists believe that sometime between 3.5 and 3.8 billion years ago there was a tipping point, something that kickstarted the change from prebiotic chemistry -- molecules before life -- to living, biological systems," Nanda said. "We believe the change was sparked by a few 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. The researchers are seeking to understand how proteins evolved to become the predominant catalyst of life on Earth.
When scouring the universe with telescopes and probes for signs of past, present or emerging life, NASA scientists look for specific "biosignatures" known to be harbingers of life. Peptides like nickelback could become the latest biosignature employed by NASA to detect planets on the verge of producing life, Nanda said.
An original instigating chemical, the researchers reasoned, would need to be simple enough to be able to assemble spontaneously in a prebiotic soup. But it would have to be sufficiently chemically active to possess the potential to take energy from the environment to drive a biochemical process.
To do so, the researchers adopted a "reductionist" approach: They started by examining existing contemporary proteins known to be associated with metabolic processes. Knowing the proteins were too complex to have emerged early on, they pared them down to their basic structure.
Researchers conducted experiments to identify the chemical that could have initiated life on Earth. They found that a peptide called Nickelback, made up of 13 amino acids and binding two nickel ions, was the best candidate. The nickel atoms in the peptide acted as catalysts, attracting protons and electrons to produce hydrogen gas, which was a vital source of energy for metabolism. This discovery is significant as it provides a laboratory-tested theory on the origins of life and suggests that simple protein metabolic enzymes could have been the starting point for life.