Peptide-nucleotide microdroplets as a step towards a membrane-free protocell model

Although phospholipid bilayers are ubiquitous in modern cells, their impermeability, lack of dynamic properties, and synthetic complexity are difficult to reconcile with plausible pathways of proto-metabolism, growth and division. Here, we present an alternative membrane-free model, which demonstrates that low-molecular-weight mononucleotides and simple cationic peptides spontaneously accumulate in water into microdroplets that are stable to changes in temperature and salt concentration, undergo pH-induced cycles of growth and decay, and promote alpha-helical peptide secondary structure. Moreover, the microdroplets selectively sequester porphyrins, inorganic nanoparticles and enzymes to generate supramolecular stacked arrays of light-harvesting molecules, nanoparticle-mediated oxidase activity, and enhanced rates of glucose phosphorylation, respectively. Taken together, our results suggest that peptide-nucleotide microdroplets can be considered as a new type of protocell model that could be used to develop novel bioreactors, primitive artificial cells and plausible pathways to prebiotic organization before the emergence of lipid-based compartmentalization on the early Earth.