Influence of amphiphile composition on properties of model primitive membranes and its implications for the origins of early cellular life

Abstract

Membrane compartmentalization is considered a feature fundamental to the origin, evolution, and maintenance of cellular life on Earth. Prebiotic membranes are thought to have preceded contemporary membranes and composed of single-chain amphiphiles (SCAs) such as fatty acids and their derivatives. Recent studies indicate that prebiotic environmental conditions would have directly influenced the biophysical properties of protocell membranes. Given this, I aimed to discern how prebiotically pertinent environmental constraints would have acted as important selection pressure(s) to shape the evolution of protocellular systems. I started out by generating model protocell membrane systems by mixing fatty acids of different chain lengths with other co-surfactants. The vesicle formation, its stability, and the properties of these model membrane systems were then evaluated as a function of multiple environmental factors, including varying pH, Mg2+ ion concentrations, dilution regimes, etc. Our results show that compositionally diverse membrane systems are amenable to readily forming compartments that are more stable and robust under multiple selection regimes. I evaluated the structural and chemical stability of these model protocellular membranes under wet-dry cycles, a geological feature with important implications for life’s origins. The change in various membrane properties and their encapsulation ability were systematically characterized. The membranes investigated were found to readily reassemble into vesicles even after multiple wet-dry cycles. This cycling induced compositional changes in these membranes, which led to changes in their physicochemical properties. Pertinently, multiple wet-dry cycles were also found to increase the vesicle’s encapsulation of small molecules. Finally, I evaluated the membrane-forming ability of dodecyl phosphate (DDP), a minimally studied prebiotically relevant SCA, as an alternative for fatty acid-based membranes. The self-assembly behavior of pure and mixed DDP membranes showed that DDP-based membranes are highly tuneable and would have been very suitable to support the emergence and evolution of protocellular life forms on the early Earth.