This 'Earthly' ancestral substance may aid in the search for alien life
Scientists working to identify the fundamental chemical processes that first powered life on Earth have discovered a portion of a protein that may have been the trigger.
Better yet, the findings could help scientists determine what to look out for on planets close to supporting life.
According to laboratory research, Rutgers scientists believe that "Nickelback," a simple peptide containing two nickel atoms, was one of the most plausible chemical choices that initiated life. A peptide is a component of a protein and is formed of a few basic amino acid building blocks.
"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," said Professor Vikas Nanda in a press release, who co-authored the study.
"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.'"
Nickelback as a biosignature for distance life
Scientists from NASA search the universe using telescopes and probes for particular "biosignatures" that are thought to be early indicators of life. According to Nanda, peptides similar to Nickelback could be the newest biosignature used by NASA to identify planets that are about to support life.
The scientists reasoned that an initial 'instigating' chemical would need to be simple enough to allow for spontaneous assembly in a prebiotic soup. Yet, it would need to be chemically active enough to have the capacity to absorb energy from the environment to power biological activity.
The researchers used a "reductionist" approach, starting by looking at proteins now known to be connected to metabolic processes. They reduced the proteins to their simplest form because they knew they were too complex to have formed during early Earth.
They reasoned that nickel was an abundant metal in the early oceans. The nickel atoms transform into powerful catalysts when attached to the peptide, drawing in more protons and electrons and generating hydrogen gas.
They also concluded that hydrogen was more prevalent on early Earth and would have been a vital energy source for metabolism.
"This is important because, while there are many theories about the origins of life, there are very few actual laboratory tests of these ideas," said Nanda.
"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," he concluded.
The study was published in Science Advances on March 10.
Ancestral metabolic processes involve the reversible oxidation of molecular hydrogen by hydrogenase. Extant hydrogenase enzymes are complex, comprising hundreds of amino acids and multiple cofactors. We designed a 13–amino acid nickel-binding peptide capable of robustly producing molecular hydrogen from protons under a wide variety of conditions. The peptide forms a di-nickel cluster structurally analogous to a Ni-Fe cluster in [NiFe] hydrogenase and the Ni-Ni cluster in acetyl-CoA synthase, two ancient, extant proteins central to metabolism. These experimental results demonstrate that modern enzymes, despite their enormous complexity, likely evolved from simple peptide precursors on early Earth.
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