Simulation Model for Functionalized Vesicles: Lipid-Peptide Integration in Minimal Protocells

A recently developed and presented stochastic simulation platform ('ENVIRONMENT' [12, 25]), which extends Gillespie's algorithm for chemically reacting, fixed-volume, homogeneous systems to volume-changing and globally heterogeneous conditions, is applied to investigate the dynamic behaviour of self-(re-)producing vesicles whose membrane consists of both lipids and small peptides. We claim that it is through the integration of these two types of relatively simple -and prebiotically plausible- components that protocells could start their development into functional supramolecular structures, allowing the formation of increasingly complex reaction networks in their internal aqueous milieu. The model is not spatially explicit, but takes into account quite realistically volume-surface constraints, osmotic pressure, diffusion/transport processes, structural elasticity. In this framework the time evolution of non-equilibrium proto-metabolic cellular systems is studied, paying special attention to the capacity of the system to get rid of its waste material, which proved critical for balanced cell growth (avoiding the risk of an osmotic burst). We also investigate the effects of including an explicit feedback mechanism in the system: the case in which waste transport mediated by peptide chains takes place only under osmotic stress conditions.