A computer rendering of the Nickelback peptide shows the backbone nitrogen atoms (blue) linking two critical nickel atoms (orange). Scientists who have identified this part of a protein believe it could provide clues to detect planets about to produce life. Credit: The Nanda Lab A team of Rutgers scientists dedicated to identifying the primordial origins of metabolism, a set of fundamental chemical reactions that first fueled life on Earth, has identified part of a protein that could provide scientists with clues to detect planets about to produce life. The research, published in Scientists Progress, has important implications for the search for extraterrestrial life because it gives researchers a new clue to look for, said Vikas Nanda, a researcher at Rutgers’ Center for Biotechnology and Advanced Medicine (CABM).
Based on laboratory studies, the Rutgers scientists say that one of the most likely chemical candidates for causing life was a simple peptide with two nickel atoms that they call “Nickelback” not because it has anything to do with the nickel band. Canadian rock, but because its backbone is nitrogen. The atoms are attached to two critical nickel atoms. A peptide is a constituent of a protein made up of a few building blocks known as amino acids. “Scientists believe that between 3.5 and 3.8 billion years ago there was a tipping point, something that triggered the shift from prebiotic (pre-life molecules) chemistry to living biological systems,” Nanda said. ‘We think the change was caused by a few small precursor proteins that performed key steps in an ancient metabolic reaction. And we think we have 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 NASA’s Astrobiology Program. Researchers seek to understand how proteins evolved to become the main enabler of life on Earth. NB structure model and comparison with natural enzymes. [Ni-Fe] hydrogenase (left) (PDB ID: 5XLE) and ACS (right) (PDB ID: 1RU3) are large complex proteins with active dimetallic sites coordinated by few ligands. The NB model structure (middle) combines elements from both active sites into a 13-residue polypeptide. Credit: Scientists Progress (2023). DOI: 10.1126/sciadv.abq1990
By scanning the universe with telescopes and probes for signs of past, present, or emerging life, NASA scientists search for specific “biosignatures” known as precursors of life. Peptides like nickel could become the latest biosignature used by NASA to detect planets about to produce life, Nanda said. According to the researchers, an original trigger chemical should be simple enough to spontaneously assemble into a prebiotic soup. But it would have to be chemically active enough to have the potential to extract energy from the environment to drive a biochemical process.
To do this, the researchers took a “reductionist” approach: They started by looking at existing contemporary proteins known to be associated with metabolic processes. Knowing that proteins were too complex to have appeared very early, they reduced them to their basic structure. After sequences of experiments, the researchers concluded that the best candidate was Nickelback. The peptide is made up of 13 amino acids and is bound to two nickel ions.
Nickel, they thought, was an abundant metal in the early oceans. When attached to the peptide, the nickel atoms become powerful 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 an essential energy source to fuel metabolism. “This is important because while there are many theories about the origins of life, there is very little actual laboratory evidence for these ideas,” Nanda said.
More information: Jennifer Timm et al, Design of a Minimal Di-Nickel Hydrogenase Peptide, Scientists Progress (2023). DOI: 10.1126/sciadv.abq1990. www.science.org/doi/10.1126/sciadv.abq1990