Shaping membrane biointerfaces: shape-adaptation in giant vesicles powered by osmotic stresses

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Nontechnical AbstractChanges in the environment such as freezing or evaporation cause changes in the concentration of salt in the environment of cells and exert stress on the cells. A physical measure of this stress are changes in the osmotic pressure. If left unchecked, changes in the osmotic pressure could cause an instantaneous flow of water out of the cell when the concentration of salt in the cell environment increases and into the cell when the concentration of salt decreases. In the former case the cell shrinks due to dehydration; in the latter case, the cell swells, and may rupture and die. To avoid these catastrophic outcomes, cells have evolved sophisticated mechanisms to regulate their water content in response to changes in the osmotic pressure caused by variations in their local environments. Primitive cells near the dawn of life on Earth on the other hand are likely to have lacked the mechanisms present in today's cells. This proposal makes use of minimal model cells to examine simple mechanisms that could have helped primitive cells to survive changes in osmotic pressure. The proposed research is also providing design rules for synthetic cells capable of responding to chemical stimuli (e.g., osmotic stress) from their environment. A working hypothesis of this effort is that the flexible membrane of the primitive cell responds to osmotic stress by changing its shape and internal organization. The effort integrates fundamental scientific research with (1) education of both undergraduate and graduate students through an interdisciplinary course on physical biology; (2) engagement of underrepresented undergraduate students in STEM research through the Vertically-Integrated-Program at UC Davis; (3) creating opportunities for undergraduate students to participate in collaborative international research at NTU, Singapore, Sorbonne, France; or Chalmers, Sweden; and (4) public dissemination of science through general talks, interviews, and forums surrounding the art and science of living matter. Technical AbstractThe proposed research tests the hypothesis that cell-sized giant vesicles consisting of lipids alone respond to environmental osmotic stress by actively reorganizing the membrane components and undergoing shape remodeling. The investigators seek to obtain a fundamental understanding of how mechanical processes at the soft and flexible membrane interfaces contribute to the balance between stability and adaptability of cells subjected to environmental changes. A long-term expectation is that these efforts will furnish fundamental design principles and experimental capabilities to synthesize active, dynamic, and reconfigurable bio-inspired synthetic compartments and interfaces that display stimuli-responsive behavior and complex, emergent, and life-like functions. The proposed effort seeks to design and construct molecularly tailored giant lipid vesicles that are synthetic cell-sized compartments. These vesicles are subject to controlled osmotic stress, including upshifts and downshifts of the osmotic pressure that take place abruptly or gradually and to uniform or gradient perturbations. The structural adaptability of the vesicles is evaluated by monitoring the molecular redistributions and shape transitions in single vesicles and in ensembles of vesicles primarily using time-resolved fluorescence microscopy. The researchers also seek to create research, educational and outreach opportunities for graduate and undergraduate students that will foster their growth into skilled scientists.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.