Protocell Formations and Polymeric Molecules      Nature Communications 23 Nov 2020

Protocell compartments, used as models for an important step in the early evolution of life on Earth, can be made from short polymers. Protocell compartments form through liquid-liquid phase separation. Although they have no membrane separating them from their environment, the protocells can sequester RNA and maintain distinct internal microenvironments.

An important step for the early evolution of life on Earth is compartmentalization, thus making synthetic compartments that could function like protocells out of molecules that were more similar in size to the molecules that would have been available on Earth when life is a way of looking at the origin of cells.

Protocells are 'complex coacervates' made by combining two oppositely charged polymers in a solution. The polymers are attracted to each other and can form droplets through liquid-liquid phase separation, similar to oil droplets forming in a salad dressing as it separates. Polymers as short as five units long could form stable compartments. In a variety of salt concentrations these protocells were able to maintain an apparent pH inside that was different than the pH of the surrounding solution.

When single-stranded RNA molecules were added to the solution, compartments made from shorter polymers were better able to sequester the RNA and the RNA molecules inside the compartments were concentrated by as much as 500 times more than the surrounding solution. Double-stranded RNA molecules were also sequestered by the compartments and were more stable in the compartments made from shorter polymers. The RNAs formed some  of its secondary structure, but did not maintain its fully native folding inside the compartments.

These synthetic vesiciles capture the essence of plausible early-Earth molecules and suggest a feasible for a mechanism of the establishment of cell-like structure on early Earth.

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