Mineral Surface-Mediated Processes in Protocell Evolution: Membrane Self-Assembly and Emergence of Energy Transduction

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(1) Technical abstractWe propose that geochemical aqueous environment chemistry played an important role in selecting lipid membrane compositions that were stable (survival of the fittest protocells). We will use model "protocells" consisting of single-chain, multi-component amphiphile vesicles as a prebiotic analog to biological membrane-forming lipids. We will determine which mixed amphiphile compositions are stable under changing environmental solution conditions. Surviving vesicle populations will be quantitatively identified by fluorometry and UV-Vis spectroscopy and fittest amphiphile concentrations will be determined by high-pressure liquid chromatography. These vesicle compositions will be considered as the "fittest." Vesicle stability will be examined for a wide range of solution pHs and in the absence or presence of dissolved salts (NaCl, KCl, NaBr, CaCl2, MgCl2, MgSO4, each at 0.01 and 0.1M concentrations). For a smaller number of samples, we will also examine the temperature-dependence of vesicle stability. These conditions will represent a wide range of geochemical environments, such as freshwater, alkaline or acidic lake water, intertidal zone water and seawater. Results will have implications for determining which geochemical environments would have provided a selection pressure for survival of the fittest protocells.(2) Broader significance This project aims to understand a critical aspect of the evolution of life, namely in figuring out how cells, the building blocks of life, came to exist. An essential and critical component of cells is their membranes, which encase all of their contents. These membranes are made of lipids. In the history of the Earth, it is unknown what led to the formation of stable lipid membranes. This research seeks to address this mystery by examining the behavior of analogs to biological membrane-forming lipids under conditions that represent different natural environments. In particular, this study will examine the role that mineral surfaces can play in the formation of "protocells" from lipids.In addition to this project's implications for the origin of life, increasing our fundamental understanding of the interaction between minerals and lipid membranes has implications for medical geology, nanomedicine, and the health/safety of nanotechnology.