Scientists answer the fundamental question of how life began on Earth

A group of Japanese scientists have found the missing link between chemistry and biology in the origin of life. (CREDIT: Creative Commons)

After all, the missing link is not an undiscovered fossil. It’s a tiny, self-replicating globule called a coacervate drop, designed by two researchers in Japan to represent the evolution of chemistry into biology.

They published their results in Connection with nature.

“Chemical evolution was first proposed in the 1920s as the idea that life first arose from the formation of macromolecules from simple small molecules, and these macromolecules formed molecular assemblies that could reproduce,” said first author Muneyuki Matsuo, assistant professor of chemistry at the Graduate School of Integrated Life Sciences, Hiroshima University.

“Since then, many studies have been carried out to experimentally test the RNA world hypothesis, according to which, before the evolution of DNA and proteins, there was only self-replicating genetic material. However, the origin of molecular ensembles reproducing from small molecules has remained a mystery for about a hundred years since the emergence of the chemical evolution scenario. This is the missing link between chemistry and biology in the origin of life,” he continued.

Matsuo collaborated with Kensuke Kurihara, a researcher at the KYOCERA Corporation, to answer the age-old question: How did free-form chemicals on the early Earth become life? Like many researchers, they initially thought that it was all about the environment: the ingredients were formed under high pressure and temperature, and then cooled to more favorable conditions for life. The issue was distribution.

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“Proliferation requires the spontaneous production and self-assembly of polymers under the same conditions,” Matsuo said.

They developed and synthesized a new prebiotic monomer from amino acid derivatives as a precursor to the self-assembly of primitive cells. When added to room temperature water at atmospheric pressure, the amino acid derivatives condensed to form peptides, which then spontaneously formed droplets.

The drops increased in size and number when fed more amino acids. The researchers also found that the droplets can concentrate nucleic acids – the genetic material – and are more likely to survive against external stimuli if they exhibit this function.

A group of Japanese scientists have found the missing link between chemistry and biology in the origin of life. (TEACHER: Hiroshima University)

“The droplet-based protocell could serve as a bridge between ‘chemistry’ and ‘biology’ during the origin of life,” Matsuo said. “This research could help explain the appearance of the first living organisms on the primordial Earth.”

In the first step, the amino acid thioester is oligomerized to form a peptide. Droplets are formed from the product by liquid-liquid phase separation (LLPS). Continuous addition of amino acid thioesters as a source of nutrition and physical stimulus to the droplets allows the droplets to divide while they self-replicate autocatalytically by incorporating nutrients. The persistence of a proliferating droplet reflects its ability to concentrate macromolecules such as nucleic acids. (CREDIT: Nature Communications)

The researchers plan to continue studying the process of evolution from amino acid derivatives to primitive living cells, as well as improve their platform to test and study the origin of life and continue evolution.

Conclusions:

Since the process of evolution from amino acid thioesters to primitive living beings could be realized by concentrating RNA, lipids, and peptides inside a proliferating droplet and then manifesting a biological-like function, it seems appropriate to call this scenario the “droplet world hypothesis”.

The droplet can be given various life-like functions by including alternative amino acids or peptides between the cysteine ​​and thioether moiety in the current monomer, or by using other alkylthiols as leaving groups. Interestingly, nonribosomal peptide synthesis by a similar mechanism has been found in some bacteria and eukaryotic cells.

In these in vivo peptide syntheses, amino acid thioesters function as monomers to form peptides. Droplets composed of peptides and nucleic acids and formed inside the cell can serve as sites for reactions associated with gene expression in modern cells.

These results are consistent with the scenario that the protocell was based on CDs formed by thioether reactions. Furthermore, since the drop world hypothesis was derived from model experiments, a consequence of this hypothesis is that the protocell could have arisen from CiA polymerization of monomers more primitive than amino acid thioesters. Thus, the system proposed in this study is a very powerful platform, not only to test the ancient scenario of the origin of life in the drop world, but also to develop self-sustaining materials that mimic higher life forms.

“By designing peptide droplets that proliferate when fed new amino acid derivatives, we experimentally cleared up a long-standing mystery of how prebiotic ancestors could reproduce and survive by selectively concentrating prebiotic chemicals,” Matsuo said. “Instead of an RNA world, we found that ‘droplet world’ may be a more accurate description, as our results indicate that the droplets became evolving molecular aggregates, one of which became our common ancestor.”

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Note: Materials provided above by the University of Hiroshima. Content can be edited for style and length.

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