A fundamental consequence of cellular organization of living systems is that the aqueous milieu, bathing the cells, is also compartmentalized. Although water equilibrates readily across the elastic cellular boundary, passive permeation of solutes is strongly hindered. As a result, gradients of concentrations of ions, salt, and soluble biomolecules are readily established across the cellular boundary, producing osmotic activity of water. To deal with any sudden environmental changes in the amount of dissolved molecules in water, free-living cells have evolved complex molecular machinaries and mechanisms (e.g., mechanosensitive channels and compatible solute accumulation), which allows them to dissipate the osmotic stress. But how might primitive cells near the dawn of life on Earth – lacking advanced biochemical or genetic capabilities and composed essentially of simple amphiphiles– have responded to such environmental insults?<br/><br/>Drawing from recent experiments in our labs employing simple models for the cellular chassis (i.e., giant vesicles composed of amphiphilic lipids and polymers), this talk considers how the osmotic activity of water is transduced across cell-like compartments. It highlights how water activity and accompanying dissipation of osmotic energy couples with the compartmental boundary, mechanically remodeling the membrane shape and spatially reorganizing membrane components - both through a well-orchestrated cooperative dynamics. Comparing these processes as elemental events in the homeostatic working of a living cell, these findings support the idea that water is not a mere solvent for life – a blank canvas on which biomolecules become animated – but an active medium that guides organization and dynamics of biomolecules in complex, subtle and essential ways.<br/><br/>The work is carried out with Doug Gettel, Jeremy Sanborn, Sean Hong, Kamila Oglecka, James Ho, Madhavan Nallani, Rachel Kraut, and Bo Liedberg.

Dissipative and dynamic self-assembly: Spontaneous osmoregulation in giant vesicles

251st National Meeting (2016)

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