Compartmentalization in an evaporating droplet suggests a feasible route to concentrate biomolecules

How life originated on the Earth is one of the most fundamental questions in modern science. Concentration and compartmentalization of the early functional biomolecules and their precursors were essential to furnish the first living cells. As a strategy to spatiotemporallly control intracellular biological reactions, liquid-liquid phase separation (LLPS) is recently proposed as a mechanism that may explain how functional biopolymers, such as RNA and proteins, can self-organize into liquid-like microdroplets inside cells. LLPS has been as a process that helps to concentrate early biomolecules and form various assemblies and compartments. However, unlike LLPS inside living cells, phase separation in the dilute and stochastic “primordial soup” is challenged by the unfavorablly high entropy and weak molecular interactions.

Recently, PhD student Wei Guo and a team led by Professor Anderson Shum from HKU Department of Mechanical Engineering and their collaborators from HKU School of Biomedical Sciences reported a prebiotically plausible pathway for biomolecule compartmentalization through the evaporation of an all-aqueous sessile droplet containing polyethylene glycol (PEG) and dextran. The water loss driven by evaporation increases the polymer concentrations, resulting in separation into PEG-rich phase and dextran-rich phase. Due to the non-uniform evaporation rate, the drying droplets exhibit interesting self-organization patterns and rich phase separation kinetics. More importantly, the resulting compartmentalization enables droplet reactions, as demonstrated by the localization and storage of nucleic acids, in vitro transcription, as well as a 3-fold enhancement of ribozyme activity. The paper was recently published in Nature Communications under the title “Non-associative phase separation in an evaporating droplet as a model for prebiotic compartmentalization”.