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

项目摘要 细胞生物学以及组织生理学和生物体的正常运作的许多方面是 材料科学中的本质问题。能使细胞正常运作的结构和反应 生物体需要产生比随机布朗运动产生的运动更大的运动。 细胞需要建造足够强大的结构来抵抗重力和机械 由相同的分子结构和细胞组装产生的压力，这些结构和细胞组装进化成 运动和力量。软物质中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 并被送到内部。这款Mira应用程序结合了两项物理研究。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类的脂类双层的生物物理和生化特性 确定这些脂质如何分布在动态膜中，以及该组织如何影响它们的控制 细胞内蛋白质靶标。 我们已经刻画并与理论家合作，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，以及 展示了这些物理模型如何帮助解释细胞和组织机制。我们还展示了它的重要性 底物的粘弹性特性与细胞表型有关，并已开发出用于 研究它们。在膜研究中，我们与分子动力学专家合作，产生一个连贯的 阴离子信号脂的结构和运动模型，如PIP2，从原子到 分子，到宏观的膜尺度。生化和细胞研究表明，空间 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。 未来的工作将建立在三个不同领域的这些研究的基础上。我们将使用我们已建立的模型 半柔性网络，以确定为什么波形蛋白网络，而不是由更坚硬的聚合物形成的网络， 压缩时会变得更硬，而交联的肌动蛋白或微管会变得更软。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，以及与液体颗粒和 核基质中的细胞器。在这里，我们将使用我们新开发的方法来完整地准备 由薄层或细胞质和质膜包围的代谢活跃的核，并确定 核周波形蛋白笼如何影响核的结构和力学响应。 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，以研究细胞内钙或钙离子的变化如何触发PIP2分布的相似变化 胆固醇影响完整细胞中肌动蛋白的组装。我们还将以相对较小的MD模拟为基础 使用当前全原子识别的基本特征对膜系统进行粗粒模拟 模拟。这些将使研究足够大并持续足够长时间的系统成为可能 产生相变和纳米级的脂簇。这些模型将被用来预测不同 PIP2结合蛋白对脂质的横向分布做出反应，并在细胞内用生化方法测试这些想法。

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.