ELSI scientists are discovering a new chemistry that could help explain the origins of cell life

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ELSI scientists are discovering a new chemistry that could help explain the origins of cell life

Chemists find simplest organic molecules can self-assemble to give cell-like structures under early Earth conditions

Before life on Earth began, the environment probably contained a large number of chemicals that reacted with each other in a more or less random way, and it is not clear how such complex things as cells could emerge from this chemical chaos. Today, a team led by Tony Z. Jia of the Earth-Life Science Institute (ELSI) of the Tokyo Institute of Technology and Kuhan Chandru of the National University of Malaysia, showed that simple α-hydroxy acids, such as glycolic and lactic acid (which is used in common facial gels), spontaneously polymerize and assemble into polyester droplets when dried at medium temperature followed by rehydration, as may have been found on beaches or banks of primary rivers and drying balls. These form a new type of cell-type compartment that can trap and concentrate biomolecules such as nucleic acids and proteins. These droplets, unlike most modern cells, are able to fuse and reform easily and may therefore have hosted early polyvalent genetic and metabolic systems that are potentially critical to the origins of life.

Scientists around the world are actively working to understand how life began. All modern earthly life, from bacteria to humans, is composed of cells. Cells are composed of lipids, proteins and nucleic acids, the lipids forming the cell membrane, an enclosure that holds the other components together and interfaces with the environment, exchanging food and waste. How molecular assemblies as complex as the cells originally formed remain a mystery.

Most research on the origins of life focuses on how molecules and structures in contemporary life were produced by the environment and then assembled into structures that led to the first cells. However, there were probably many other types of molecules that formed at the same time as biomolecules on the early Earth, and it is possible that life began to use a very simple chemistry unrelated to modern biomolecules, then evolved through increasingly complex steps to give birth to modern cell structures.

Previous work at ELSI has shown that the moderate temperature drying of simple organic compounds known as alpha-hydroxy acids, found in meteorites and numerous simulations of prebiological chemistry, spontaneously polymerizes them into mixtures of long polyesters. Based on this work, Jia and her colleagues then examined these reactions under the microscope and found that these polyester composite systems form a gel phase and self-assemble spontaneously when re-wetted to form simple cell-shaped structures.

The most difficult aspect of this work was to develop new methods to characterize the properties and functions of droplets, as no one had yet analyzed such systems. Jia noted that the team was fortunate to have such a diversity of multidisciplinary expertise, including chemists, biochemists, materials specialists and geologists. After determining their composition and showing their tendency to self-assemble, the next question was whether these cellular structures might be able to do something chemically useful. Modern cell membranes perform many crucial functions that help maintain the cell; for example, they retain macromolecules and metabolites in one place, while providing a constant internal environment, which can be very different from that outside the cell. They first measured the stability of these structures and found that they could persist for very long periods of time depending on environmental conditions, but that they could also be fused and fused.

They then tested the ability of these structures to sequester molecules from the environment and discovered that they accumulated large dye molecules to a remarkable degree. They then showed that these droplets could also contain RNA and protein molecules and allow them to be functionally catalytic. In addition, the team demonstrated that droplets could help to form a lipid layer on their surface, suggesting that they could have helped to form protocells.

Jia and her colleagues are not sure if these structures are the direct ancestors of the cells, but they think it is possible that such droplets may have allowed the assembly of protocells on Earth. The new system of compartmentalization they have found is extremely simple, they note, and could easily be formed in the primitive environments of the Universe. This allows us to imagine non-biological systems on the early Earth that may still have played a role in the origins of life on Earth," says Jia. This suggests that there may be many other non-biological systems that should be the subject of future research of this type." He believes that the development of these or similar model systems could better study the evolution of various chemical systems representative of the complex chemistry likely to be found on early planetary bodies.

"The primitive Earth was certainly a chemically disordered place," explains Jia, "and often most life studies focus on modern biomolecules under relatively "clean" conditions. It may be important to take these "messy" mixtures and see if there are any interesting functions or structures that can arise spontaneously." The authors now believe that by systematically increasing the chemical complexity of these systems, they will be able to observe their evolution over time and perhaps discover divergent and emerging properties.

"We have this new experimental system that we can now play with, so that we can start studying phenomena like the evolution and evolution of these droplets. The possible combinations of structures or functions that these droplets can have are almost infinite. While the physical rules governing droplet formation are quite universal in nature, we hope to study similar systems to find out if they can also form microdroplets with new properties," adds Jia.

Finally, although the team is currently focusing on understanding the origins of life, it notes that this fundamental research could have applications in other areas, such as drug delivery and personalized medicine. "This is just one wonderful example of the unexpected ways projects can develop when a team of scientists from around the world come together to try to understand new and interesting phenomena," said Jim Cleaves, also a member of ELSI.