Design of Fuel-Dependent, Complex-Coacervate-Based Synthetic Cells.

Fuel-dependent synthetic cells are compartments that require fuel to emerge and sustain. Without fuel, they decay, serving as a selection pressure in fueling-starvation experiments. Recently, we introduced fuel-dependent synthetic cells based on droplets as a route to synthetic life. These droplets grow, divide, and decay under starvation conditions. However, which parameters influence their lifetime and their ability to divide remain unknown. Moreover, previous designs of these synthetic cells suffer from the accumulation of waste products of their chemical reactions. In this work, we offer design rules for chemically fueled complex coacervate droplets with a focus on hexapeptides. We find that incorporating tryptophan into peptide designs increases the peptides' affinity for polyanions and thus their ability to form droplets. The resulting synthetic cells are longer-lived and more waste-resistant and can produce offspring when RNA is used as the polyanion. Placing the tryptophan close to the reactive C-terminus further extends the droplet lifetime by slowing deactivation. Together, these results lead to a new series of peptides to produce waste-resistant, RNA-compatible, fuel-dependent synthetic cells.