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

【非技术内容】冷冻、蒸发等环境变化引起细胞环境中盐浓度的变化，对细胞产生应激作用。这种压力的物理测量是渗透压的变化。如果不加以控制，当细胞环境中的盐浓度增加时，渗透压的变化可能会导致水瞬间流出细胞，而当盐浓度降低时，水又流入细胞。在前一种情况下，细胞因脱水而收缩；在后一种情况下，细胞肿胀，并可能破裂和死亡。为了避免这些灾难性的结果，细胞已经进化出复杂的机制来调节其含水量，以响应由局部环境变化引起的渗透压变化。另一方面，地球上生命出现初期的原始细胞很可能缺乏今天细胞中存在的机制。这个建议利用最小的模型细胞来检查可能帮助原始细胞在渗透压变化中生存的简单机制。拟议的研究还为能够对环境中的化学刺激（例如渗透压力）做出反应的合成细胞提供了设计规则。这种努力的一个有效假设是，原始细胞的柔性膜通过改变其形状和内部组织来响应渗透压力。这项工作将基础科学研究与(1)通过物理生物学的跨学科课程对本科生和研究生进行教育；(2)通过加州大学戴维斯分校的垂直整合项目，让代表性不足的本科生参与STEM研究；(3)为本科生在南洋理工大学、新加坡、法国索邦大学创造参与国际合作研究的机会；或瑞典查尔默斯；(4)通过围绕生命物质的艺术和科学的一般性讲座、访谈和论坛，向公众传播科学。摘要本研究验证了细胞大小的由脂质组成的巨囊泡对环境渗透胁迫的反应是通过主动重组膜组分并进行形状重塑。研究人员试图对软性和柔性膜界面的机械过程如何促进细胞在环境变化下的稳定性和适应性之间的平衡有一个基本的了解。一个长期的期望是，这些努力将提供基本的设计原则和实验能力，以合成主动的、动态的和可重构的生物启发合成隔间和界面，显示刺激响应行为和复杂的、紧急的和类似生命的功能。提出的努力旨在设计和构建分子定制的巨型脂质囊泡，这是合成细胞大小的隔室。这些囊泡受到可控的渗透胁迫，包括突然或逐渐发生的渗透压上升和下降，以及均匀或梯度扰动。通过主要使用时间分辨荧光显微镜监测单个囊泡和囊泡群中的分子重新分布和形状转变来评估囊泡的结构适应性。研究人员还寻求为研究生和本科生创造研究、教育和推广机会，以培养他们成长为熟练的科学家。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.