Researchers believe that they have identified the core elements of the first proteins that made life possible. If they are right, it can open new doors to understand the great question of how and under what circumstances life can come out of a living world.
There are many lines of exploration and debate about where life began and whether DNA, RNA, or a mixture came first. Researchers at Rutgers University are exploring the issue from a different angle, trying to identify the ancestral proteins we all came from. They have provided some possible answers, published in the journal Science Advances.
Collecting and using energy are essential characteristics of life, the researchers reasoned. Whatever the source of the energy, its chemical storage and use involves the transfer of electrons, and this must have been true from the beginning. When life had just begun, it makes sense that it has used the most readily available electron conductors, they continued. In the early seas, this would have been the small subset of transition metals that were soluble under today's conditions.
Therefore, proteins that bind metals must have been original to life, with many subsequent biological functions performed by recycled versions of these original proteins. Metal binding is still essential to life today, so the authors sought the structure of the original proteins by looking for common features in proteins that fulfill this role across the tree of life. They report common features in almost all transition metal binding proteins, regardless of their function, the organism they come from, or the metal being treated.
"We saw that the metal-binding nuclei of existing proteins are actually similar, although the proteins themselves may not be," said study author Professor Yana Bromberg in a statement.
"We also saw that these metal-binding nuclei often consist of repeated substructures, like LEGO bricks. Oddly enough, these blocks were also found in other areas of the proteins, not just metal-binding nuclei, and in many other proteins that were not taken into account in our study Our observation suggests that rearrangements of these small building blocks may have had a single or a small number of common ancestors and given rise to the whole range of proteins and their functions that are currently available - ie to life, which we know that. "
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.
After the great oxidation event, proteins diversified and folded in an abundance of new and more complex ways. The authors believe that this makes it too difficult to identify the original sequences, but consider it possible to trace the development of protein components based on their structures. In the process, they identified distantly related peptides (short chains of amino acids that can form the building blocks of proteins) using their structural adaptations.
Bromberg noted that this, like any insight into how life originated, could prove useful in searching for life beyond Earth, as well as in the search for creating new living things through synthetic biology.