SHARING OF STRAIN BETWEEN SOFT BIOLOGICAL ASSEMBLIES AND SYNTHETIC LIQUID CRYSTALS
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Management of mechanical forces is one of the central principles of biology, yet it remains poorly understood in contexts ranging from life-threatening diseases like malaria to fundamental processes such as plant photosynthesis. This thesis explores how soft biological assemblies (vesicles, mammalian cells, and plant organelles) respond structurally and functionally to mechanical stresses imparted by aqueous nematic liquid crystals (LCs).First, we describe LC-induced straining of giant plasma membrane vesicles (GPMVs) derived from epithelial cells that express high levels of the cancer-associated glycoprotein Muc1. Single-vesicle-level characterization of GPMV size and Muc1 density reveals that their sizes and Muc1 densities are correlated, suggesting the role of Muc1 in controlling the sizes of plasma membrane blebs. Additionally, analysis of the GPMV shape-response to LC elasticity reveals that Muc1, previously reported to induce morphological changes on cell surfaces, has no influence on the mechanical properties of GPMVs, suggesting that the membranes of GPMVs are different in composition and mechanical properties to their parent cells. Infection of red blood cells (RBCs) by apicomplexan parasites can rigidify them and make them adhere to the walls of blood vessels (‘cytoadherence’) to survive the rigidity-based filtration by the spleen. While previous studies have established that rigidification and cytoadherence are correlated for Plasmodium infection of human RBCs, by characterizing the mechanical properties of RBCs using LCs, we reveal that this correlation also exists for Babesia infection of bovine RBCs, however, parasite proteins that enable cytoadherence of RBCs have no influence on their rigidification. Finally, we show that chloroplasts isolated from spinach leaves can be mechanically strained by LCs in a tunable manner. By measuring the rate of reduction of an electron acceptor dye, we reveal a reversible strain-dependent decrease in the photosynthetic activity of chloroplasts, with up to 80% reduction in activity for 40% strain. These findings uncover novel mechanisms by which mechanical stresses influence plant growth at the organelle level. Taken together, our findings provide new fundamental insights into the implications of mechanical stresses on soft biological assemblies and advance methodologies that enable biophysical studies in diverse systems.