Lipid assembly on a polyphenyllactate droplet surface to form a hybrid protocell

Deciphering how primitive, inanimate matter organized into living systems is a central challenge in origins of life research. In this context, protocells—primitive cell-like compartments—are widely considered as plausible intermediates linking nonliving chemistry with early biological systems. Among various protocell models, formation of polyester droplets through wet-dry cycle-induced polymerization of hydroxy acids, followed by hydration, provides a prebiotically plausible model of primitive compartment formation on early Earth, resulting in a membraneless protocell providing relevant functions such as biomolecule enrichment. However, these droplets, while functional to some extent, may have necessarily required incorporation of membrane boundaries to support their stability and their potential to evolve over extended timescales. Here, we report the construction of lipid-coated polyphenyllactate (polyPA) droplets, in which lipid layers spontaneously assemble onto droplets to form stable membrane-bound compartments. By integrating the robustness of lipid bilayers with the molecular enrichment properties of polyPA droplets, lipid-coated polyPA droplets exhibit permeability to small molecules as well as significantly enhanced stability compared to membraneless polyPA droplets. This hybrid model protocell system provides a plausible bridge providing a transition from membraneless to membrane-bound protocells, a potential essential step leading towards the emergence of early cellular life.