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bioRxiv · 10.1101/678847

Compositional heterogeneity of protocellular membranes: Implications for emergence of mixed vesicular systems

Sarkar, S.·Dagar, S.·Verma, A.·Rajamani, S.
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Abstract

Protocells are primitive cellular entities that are thought to have emerged during the dawn of life on Earth. Their membranes are considered to be made up of mixtures of single chain amphiphiles, such as fatty acids and their derivatives, moieties that would have been part of the complex prebiotic chemical landscape. In addition to their composition, the physico-chemical properties of these prebiological membranes would have been significantly affected and regulated by the physical environment that they were present in. In this study, the physico-chemical properties of two different chain length membrane systems were systematically characterized, under pertinent early Earth conditions. The membrane systems were designed to comprise a fatty acid and its alcohol and/or glycerol monoester derivative, to make a range of binary and tertiary vesicle combinations. Their properties were then evaluated as a function of multiple factors including their composition, stability under varying pH, Mg2+ ion concentrations and dilution regimes, and their permeability to small molecules. Our results demonstrate how these environmental constraints would have acted as important prebiotic selection pressures to shape the evolution of prebiological membranes. This study also illustrates how different fatty acid derivatives confer varying degree of stability when combined with their respective fatty acid moiety. Interestingly, when the membrane systems were subjected to multiple selection pressures in a consecutive manner, only the heterogeneous membrane systems survived the race. Our results illustrate that compositionally diverse membrane systems are more stable and robust to multiple selection pressures, thereby making them more suitable for supporting protocellular life.\n\nSignificance statementThe physico-chemical environment would have played an important role in shaping the composition and evolution of primitive membrane systems. This study demonstrates the importance of compositional heterogeneity on the stability of protomembrane systems under pertinent prebiotic selection pressures. Two different fatty acid based systems were mixed with their respective alcohol and/or glycerol monoester derivatives, to generate combinations of binary and tertiary membrane systems. Increasing chain length effected the physical property of the membranes thus affecting their stability. Furthermore, we also demonstrate how the head groups of the derivatives employed in this study (e.g. glycerol monoester and alcohol) contribute differently towards stabilizing the mixed membranes under a given selection condition, by discerning the molecular mechanism underlying this process. Our results illustrate how multiple selection pressures would have preferentially supported the emergence of compositionally heterogeneous membrane systems.

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Sarkar, S., Dagar, S., Verma, A., Rajamani, S.. 2019-06-21. Compositional heterogeneity of protocellular membranes: Implications for emergence of mixed vesicular systems. https://doi.org/10.1101/678847

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