Reprogramming materials properties of synapsin self-coacervates via phosphorylation code

非技术总结也许在寻找细胞内的结构，以激发下一代新材料的最有趣的方面是不是他们的整体结构特性，但细胞的能力，“重新编程”这些结构。就像重新编程软件可以执行不同的任务一样，重新编程材料可以让它们在生产后承担新的功能。这在相分离成富含蛋白质和蛋白质稀液相的选择蛋白质中尤其明显，就像添加到水中的油将分离成富含油的液相一样。这种相分离已被证明是由磷酸化控制的，或向蛋白质中添加带电的磷酸基团。并非所有的磷酸化都是平等的;蛋白质内某些位点的磷酸化将消除相分离的能力，而其他位点仍然可以控制分子进出富含蛋白质的液相的运输。然而，不能同时评估细胞中富含蛋白质的液相的磷酸化序列（或“磷酸化密码”）和相应的材料性质使得难以设计提供类似重编程能力的合成材料。本项目试图通过使用新的生物化学工程技术来制造具有特定磷酸化密码的蛋白质，并随后测量这些相分离蛋白质的材料特性，从而克服这一障碍。在这样做的过程中，将创建一个框架来设计具有类似重编程能力的其他材料，并可能产生一类新的仿生材料用于治疗和消费用途。除此之外，考虑到多学科科学和工程的要求，该项目不仅将为下一代跨学科科学家提供培训机会，而且将通过为大洛杉矶地区当地社区学院的学生提供研究机会来寻求扩大这一渠道。技术概述内插无序蛋白（IDP）作为生物聚合物在溶液中持续存在，并且可以经历相分离成富含蛋白质的液滴，类似于聚合物凝聚。这些亚细胞结构具有独特的目的，从细胞器隔离到潜在的细胞内生物反应器。然而，生物学已经建立了一个额外的复杂层; IDP可以通过翻译后修饰来“重编程”以改变材料性质，从而实现一系列动态性质，这对于良好折叠的蛋白质是不切实际的。（或添加带二价电荷的磷酸基团），已经显示出独立地控制突触蛋白的相行为和生物大分子运输性质，突触蛋白是在神经元内形成富含突触蛋白的液滴的IDP。虽然控制这些特性是生物材料研究的一个诱人目标，但破译可能发生在多个不同位点的修饰的“磷酸化密码”并将这些密码与其所得生物功能相关联仍然是一个具有挑战性的障碍。为了克服这一障碍，聚合物科学和物理化学的见解将用于靶向最有可能改变材料特性的特定磷酸化密码。然后，无细胞蛋白质合成策略将用于表达和纯化具有特定磷酸化密码的突触蛋白，并测量其所得生物材料的性质。最终，这些数据将形成一个设计框架的基础，该框架对其他基于IDP的生物材料甚至合成聚合物系统的重新编程具有解释和预测能力。该奖项反映了NSF的法定使命，并被认为值得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来支持。

NON-TECHNICAL SUMMARYPerhaps the most intriguing aspect in looking to structures within the cell to inspire the next generation of novel materials is not their bulk structural properties but the cellular ability to “reprogram” these structures. Much as reprogramming software allows it to perform different tasks, reprogramming materials allows them to take on novel functions after production. This is especially evident in select proteins that phase separate into protein-rich and protein-dilute liquid phases, much as oil added to water will separate into an oil-rich liquid phase. This phase separation has been shown to be controlled by phosphorylation, or the addition of a charged phosphate group to the protein. Not all phosphorylations are created equal; phosphorylation at certain sites within the protein will eliminate the ability to phase separate while others still can control the transport of molecules in-and-out of the protein-rich liquid phase. However, the inability to simultaneously assess the sequence of phosphorylation (or “phosphorylation code”) and the corresponding materials properties of the protein-rich liquid phase in the cell has made it difficult to design synthetic materials that offer similar reprogramming capability. This project seeks to overcome this obstacle by using novel biochemical engineering techniques to manufacture proteins with specific phosphorylation codes and subsequently measure the materials properties of these phase separating-proteins. In doing so, a framework will be created to design other materials with similar reprogramming capabilities and potentially generate a new class of biomimetic materials for therapeutic and consumer use. Beyond that, given the multidisciplinary scientific and engineering requirements, this project will not only provide training opportunities for the next generation of interdisciplinary scientists but seek to expand that pipeline by providing research opportunities for students at local community colleges in the greater Los Angeles area. TECHNICAL SUMMARYIntrinsically disordered proteins (IDPs) persist as biopolymers in solution and can undergo phase separation into protein-rich liquid droplets, akin to polymer coacervation. These subcellular structures serve unique purposes, ranging from organelle sequestration to potentially behaving as bio-reactors within the cell. However, biology has built in an additional layer of sophistication; IDPs can be “reprogrammed” via post-translational modifications to alter the materials properties, enabling a range of dynamic properties that would be impractical with well-folded proteins.One particular modification, phosphorylation (or the addition of a divalently-charged phosphate group), has been shown to independently control the phase behavior and biomacromolecule transport properties of synapsin, an IDP that forms synapsin-rich liquid droplets within the neuron. While control of these properties is an inviting target for biomaterials investigation, deciphering the “phosphorylation code” of modifications that can occur at multiple, distinct sites and correlating these codes to their resultant biological function remains a challenging obstacle. To overcome this barrier, insights from polymer science and physical chemistry will be used to target specific phosphorylation codes most likely to alter materials properties. Then, cell-free protein synthesis strategies will be used to express and purify synapsin with specific phosphorylation codes and measure their resultant biomaterials properties. Ultimately, this data will form the basis of a design framework that has explanatory and predictive power for reprogramming other IDP-based biomaterials and even synthetic polymer systems.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.