Scientists think they have identified the essential elements of the first proteins that made life possible. If they’re right, it could open new doors to understanding the big question of how and under what conditions life could emerge from an inanimate world.
There is a lot of research and debate about where life began and whether it was DNA, RNA, or a mix that came first. Rutgers University researchers are exploring the question from a different angle, trying to identify the ancestral proteins we all come from. They provided some possible answers with the paper published in the journal Science Advances.
The researchers concluded that collecting and using energy are essential properties for life. Whatever the source of energy, chemical storage and use involves electron transfer, and this must be true from the start. When life was just beginning it made sense to use the most readily available electron conductors, they continued. In the early ocean, this would have been a small subset of transition metals that were soluble under the conditions of the day.
Therefore, metal-binding proteins must be original for life, with many subsequent biological functions performed by repurposed versions of these original proteins. Metal binding remains crucial to life today, so the authors sought the structure of the original proteins by looking for common features in proteins that fulfill this role in the tree of life. It reports commonalities in almost all transition metal-binding proteins, regardless of their function, the organism from which they come, or the metal being processed.
Professor Yana Bromberg said in a statement, “We found that the metal-binding cores of the existing proteins, although not the proteins themselves, are indeed similar,” and continued:
Interestingly, these blocks were found not only in metal-binding cores, but also in other regions of the proteins and many other proteins that were not considered in the study.
Observations suggest that rearrangements of these tiny building blocks may have had a single or few common ancestors, and have given rise to all the varieties of proteins and functions currently available, namely life as we know it.
The almost universal structures are mostly oxidoreductases, enzymes that transfer electrons between molecules. The authors conclude that they existed more than 3.8 billion years ago.
Following the Great Oxidation Event, proteins diversified, folding in many new and more complex ways. The authors feel that this makes it very difficult to identify the original sequences, but that it is possible to trace the evolution of protein components based on their structure. In the process, they identified distantly related peptides—short chains of amino acids that can form the building blocks of proteins—using their structural alignment.
Like any insight into how life arose, we think it could be useful in the search for life beyond Earth. . .
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