Regulation of cell function by mechanical properties of biopolymer networks and lipid bilayers

项目摘要 细胞生物学的许多方面以及组织生理学和生物体的正常功能是 本质上是材料科学的问题。一种能使细胞正常运作的结构和反应， 有机体需要产生比随机布朗运动更大的运动。 细胞需要建造足够坚固的结构来抵抗重力和机械力 应力是由相同的分子结构和细胞组装产生的， 运动和力量。软物质的一个相关问题是理解软物质的物理化学和动力学。 形成细胞膜并协调细胞产生的信号的磷脂双层 膜并发送到内部。这个MIRA应用程序结合了两个物理研究。一个是专注于 纯化的生物聚合物网络、完整细胞和整个组织的机械性能。第二 涉及含有阴离子信号脂质的脂质双层的生物物理和生物化学表征， 确定这些脂质如何在动态膜中分布，以及这种组织如何影响它们的控制 细胞内蛋白质靶点。 我们已经描述并与理论家合作，解释了 半柔性聚合物网络，重点是细胞骨架中间丝蛋白波形蛋白， 展示了这些物理模型如何帮助解释细胞和组织机制。我们也证明了 基质的粘弹性与细胞表型相关，并且已经开发了新的材料， 研究他们。在膜研究中，我们与分子动力学专家合作， 阴离子信号脂质如PIP2的结构和运动的模型，范围从原子到分子。 从分子到宏观的膜尺度。生物化学和细胞研究表明， 这些脂质在双层中的分布影响它们控制细胞骨架肌动蛋白组装的方式， 细胞质/膜界面 今后的工作将在三个不同领域的这些研究的基础上开展。我们将使用我们建立的模型 半柔性网络，以确定为什么波形蛋白网络，与那些由更硬的聚合物形成的网络相比， 当压缩时变得更硬，而交联的肌动蛋白或微管变得更软。我们还将 将我们对细胞外聚合物和细胞的研究扩展到细胞内系统：细胞骨架网络 含有膜结合的细胞器和与液体颗粒交联的DNA或染色质， 细胞器包含在核基质中。在这里，我们将使用我们新开发的方法来制备完整的 由一薄层或细胞质和质膜包围的代谢活性核，并决定 核周波形蛋白笼如何影响核的结构和机械反应。 膜研究将使用我们以前的方法来改变PIP2在人工双层和分离细胞中的分布 膜，以研究细胞内Ca2+或Ca2+浓度的变化如何引发PIP2分布的类似变化。 胆固醇影响完整细胞中肌动蛋白的组装。我们还将建立在MD模拟相对较小的 膜系统的粗粒模拟使用的基本特征确定当前的全原子 仿真。这将使研究的系统是足够大的，并遵循了足够的时间， 产生相变和纳米级脂质簇。这些模型将用于预测 PIP2结合蛋白对脂质的横向分布做出反应，并在生物化学和细胞中测试这些想法。

Project Summary Many aspects of cell biology as well as tissue physiology and the proper functioning of organisms are essentially problems in material science. The structures and reactions that enable proper functioning of an organism need to produce movements that are greater than those generated by random Brownian motion. Cells need to build structures that are strong enough to resist gravitational forces as well as the mechanical stresses that are generated by the same molecular structures and cellular assemblies that evolved to generate movement and force. A related problem in soft matter is to understand the physical chemistry and dynamics of the phospholipid bilayer that forms the cell membrane and orchestrates the signals generated at the cell membrane and sent to the interior. This MIRA application combines two physical studies. One is focused on the mechanical properties of purified biopolymer networks, intact cells, and whole tissues. The second involves biophysical and biochemical characterizations of lipid bilayers containing anionic signaling lipids to determine how these lipids distribute in the dynamic membrane and how this organization impacts their control of intracellular protein targets. We have characterized and worked with theorists to explain the striking nonlinear elastic response of semi-flexible polymeric networks, with emphasis on the cytoskeletal intermediate filament protein vimentin, and shown how these physical models help explain cell and tissue mechanism. We have also shown how important viscoelastic properties of the substrate are to cell phenotypes and have developed new materials by which to study them. In membrane studies, we collaborate with molecular dynamics experts to produce a coherent model of the structures and motions of anionic signaling lipids such as PIP2 ranging from the atomic to the molecular, to the macroscopic membrane scale. Biochemical and cellular studies show that the spatial distribution of these lipids in bilayers impacts the way they control cytoskeletal actin assembly at the cytoplasm/membrane interface. Future work will build on these studies in three different areas. We will use our established models of semiflexible networks to determine why vimentin networks, in contrast to those formed by stiffer polymers, become stiffer when compressed, whereas crosslinked actin or microtubules become softer. We will also extend our studies of extracellular polymers and cells to intracellular systems: cytoskeletal networks containing membrane-bounded organelles, and crosslinked DNA or chromatin with the liquid particles and organelles contained in the nuclear matrix. Here we will use our newly developed method to prepare intact metabolically active nuclei surrounded by a thin layer or cytoplasm and a plasma membrane, and determine how the perinuclear vimentin cage influences the structure and mechanical response of the nucleus. Membrane studies will use our previous methods to alter PIP2 distribution in artificial bilayers and isolated cell membranes, to study how similar changes in PIP2 distribution triggered by changes in intracellular Ca2+ or cholesterol affect actin assembly in intact cells. We will also build on the MD simulations of relatively small membrane systems to coarse grain simulations using the essential features identified by current all-atom simulations. These will enable studies of systems that are large enough and followed for sufficient time to produce phase transitions and nano-scale lipid clusters. These models will be used to predict how different PIP2 binding proteins respond to lateral distribution of the lipid and test these ideas biochemically and in cells.