A New Perspective on the Origins of Life on Earth

According to LMU scientists led by Thomas Carell, a unique chemical species consisting of RNA and peptides set in motion the evolution of life into increasingly sophisticated forms.

Finding out how life may have arisen so long ago on the early Earth is one of science’s most interesting challenges. What conditions were required for the basic building blocks of more complex life to emerge? One of the main possibilities is the so-called RNA universe theory, which was proposed by molecular biology pioneer Walter Gilbert in 1986. According to the idea, nucleotides — the basic building elements of the nucleic acids A, C, G, and U — formed in the primordial soup and were used to make short RNA molecules.

As a result, single-stranded RNA molecules may unite to form double strands, giving rise to the theoretical possibility that the molecules could reproduce themselves. In each example, only two nucleotides match together, indicating that one strand is the exact opposite of the other and so serves as a template for another.

This replication could have improved over time, resulting in more sophisticated life at some point. “The RNA world notion has the enormous advantage of sketching out a process where complex biomolecules like nucleic acids with specialized catalytic and information-coding characteristics can develop,” explains Thomas Carell of Ludwig Maximilian University of Munich (LMU). Double strands of DNA, a slightly modified, durable kind of macromolecule consisting of nucleotides, make up genetic material as we know it today.

The hypothesis, however, is not without flaws. RNS, for example, is a delicate molecule, especially as it grows longer. Furthermore, it is unclear how RNA molecules are linked to the world of proteins, for which the genetic material, as we all know, provides the blueprints. Carell’s working group has uncovered a possibility for this linkage to have occurred, according to a new research published in Nature.

To comprehend, we must examine RNA in further detail. RNA is a complex macromolecule in and of itself. It contains non-canonical bases, some of which have very strange structures, in addition to the four canonical bases A, C, G, and U, which carry genetic information. These non-information-coding nucleotides are critical for RNA molecules to function properly. We now know of over 120 different modified RNA nucleosides that nature incorporates into RNA molecules. They are almost certainly vestiges of the previous RNA world.

The Carell group has now established that these non-canonical nucleosides are the “secret ingredient” that permits the RNA and protein worlds to interact. According to Carell, some of these molecular fossils can “adorn” themselves with individual amino acids or even small chains of them (peptides) when found in RNA. When amino acids or peptides are present in a solution at the same time as the RNA, this results in tiny chimeric RNA-peptide structures. The amino acids and peptides linked to the RNA in such structures subsequently react with one another to generate larger and more complicated peptides. “We were able to make RNA-peptide particles in the lab that could encode genetic information and even produce lengthening peptides in this method,” says the researcher.

As a result, the ancient fossil nucleosides are similar to RNA nuclei, producing a core around which lengthy peptide chains can grow. Peptides were even developing at numerous spots on some RNA strands. “That was a pretty unexpected revelation,” Carell says. “It’s plausible that there was never a pure RNA world, but that RNA and peptides co-existed in a single molecule from the beginning.” As a result, the concept of an RNA world should be expanded to include an RNA-peptide world. According to the new theory, peptides and RNA mutually assisted each other during evolution.

The availability of RNA molecules that could adorn themselves with amino acids and peptides and therefore combine them into larger peptide structures was a vital feature in the beginning, according to the new interpretation. “RNA has developed into a better amino acid linking catalyst throughout time,” says Carell. This link between RNA and peptides or proteins has been maintained to this day. The ribosome is the most significant RNA catalyst, and it still links amino acids together to form long peptide chains. It is one of the most complicated RNA engines in the body, and it is in charge of converting genetic information into functional proteins in every cell. Carell claims that “the realm of RNA peptides thereby solves the chicken-and-egg issue.” “The new concept establishes a foundation for the origin.”