Mixed fatty acid-phospholipid protocell networks

Abstract

Self-assembled membranes composed of both fatty acids and phospholipids are both permeable for solutes and structurally stable, which was likely an advantageous combination for the development of primitive cells on the early Earth. Here we report on the solid surface-assisted formation of primitive mixed-surfactant membrane compartments, i.e. model protocells, from multilamellar lipid reservoirs composed of different ratios of fatty acids and phospholipids. Similar to the previously discovered enhancement of model protocell formation on solid substrates, we achieve spontaneous multi-step self-transformation of mixed surfactant reservoirs into closed surfactant containers, interconnected via nanotube networks. Some of the fatty acid containing compartments in the networks exhibit colony-like growth. We demonstrate that the compartments generated from fatty acid-containing phospholipid membranes feature increased permeability coefficients for molecules in the ambient solution, for fluorescein up to 7*10-6 cm/s and for RNA up to 3.5*10-6 cm/s. Our findings indicate that surface-assisted autonomous protocell formation and development, starting from mixed amphiphiles, is a plausible scenario for the early stages of the emergence of primitive cells.

Did Solid Surfaces Enable the Origin of Life?

“…They represent a local energy minimum, yet remain costly to the overall system due to high bending energy. To reduce bending energy, fragments of the The protocell networks can be formed from membranes consisting of phospholipids only, or from mixtures of phospholipids and fatty acids [35]. The networks have been shown to encapsulate water soluble compounds, even RNA and DNA [35][36][37].…”

“…To reduce bending energy, fragments of the The protocell networks can be formed from membranes consisting of phospholipids only, or from mixtures of phospholipids and fatty acids [35]. The networks have been shown to encapsulate water soluble compounds, even RNA and DNA [35][36][37]. Especially RNA has been a molecule of interest in origin of life studies, as it can act uniquely both as a genetic information carrier and an enzyme analog, catalyzing its own replication [38].…”

“…The surface-adhered compartments can grow rapidly and fuse with merging of contents [36], passively replicate by transporting material through the nanotubes [39], divide, migrate, and re-attach to a surface in remote locations [33]. The protocell networks can also grow in groups in a colony-like manner, where the membranes of the individual compartments are in physical contact with each other [35,37].…”

“…The protocell networks can be formed from membranes consisting of phospholipids only, or from mixtures of phospholipids and fatty acids [ 35 ]. The networks have been shown to encapsulate water soluble compounds, even RNA and DNA [ 35 , 36 , 37 ].…”

“…Another type of biomembrane morphology occurring as a result of surface interactions is the interconnected micro-container network [ 35 , 36 ] ( Figure 3 and Figure 4 B). The containers in such physical network may have accommodated different prebiotic chemical reaction networks [ 44 ].…”