Exploiting Engineered Polyproteins in the Modular Design of Robust, Tuneable and Biofunctional Hydrogels

蛋白质是一种生物异常机器。这些细胞的主力负责大量的生物功能。它们单独行动，或作为更大的、通常是复杂的机器的一部分，通过结构和机械变化来执行它们的功能。对自然界中发现的蛋白质的机械性能的研究为设计具有先进机械性能的新材料提供了许多灵感。这包括巨大的肌肉蛋白Titin中的高机械强度、断裂韧性和弹性与天然丝素纤维耐人寻味的机械性能的非凡结合。尽管自然界表面上的生物复杂性，但研究表明，蛋白质可以被设计成成功地模仿肌肉的力量和被动弹性。这是通过设计包含特定数量和排列的蛋白质结构域的多蛋白来实现的。多聚蛋白质很重要，因为它们在实验中提供了一个清晰的机械指纹，用于监测蛋白质对外加机械力的反应。多聚蛋白质可以用聚合物物理学来描述，也可以用单分子力谱(SMFS)等工具来操纵，单分子力谱提供了关于它们的机械稳定性和柔软性的信息。多聚蛋白质中存在的层次结构和分子间相互作用以及它们形成的网络提供了新的机会。特别是，最近一个令人兴奋的发展是使用多蛋白作为水凝胶的构建块。水凝胶是一种三维的、水合的、高度多孔的、跨越宏观维度的渗流聚合物网络。水凝胶领域现在很广泛，在英国有相当大的实力。然而，由于一种被称为重组DNA技术的生物技术的进步，基于多蛋白的水凝胶直到最近才被探索出来。由工程多蛋白组成的水凝胶具有三个关键优点：(I)多蛋白链的模块化设计可以用来模拟自然界中发现的诱人的机械和结构层次；(Ii)折叠的球状蛋白提供具有序列依赖和可调节的热力学和机械性质的构建块；(Iii)功能是蛋白质折叠所固有的，允许结合特定的生物识别能力来响应生物分子提示。因此，基于多蛋白的水凝胶是软物质和生物物理学中一个令人兴奋的新兴领域。折叠蛋白质的整体功能为组织工程和干细胞分化等应用提供了巨大的机会，并为用于微光学、生物传感器和药物控制释放的智能、响应材料提供了一条途径。虽然已经有了测量蛋白质和水凝胶的结构、动力学和力学的工具，但人们对这种信息如何在纳米和介观长度尺度之间转换知之甚少。系统和合理的水凝胶设计方法要求在层级组织的所有级别上了解体系的机械和结构属性。这项研究将为生产具有特定生物功能能力的多蛋白水凝胶提供一个平台，使机械和结构特性能够响应生物分子线索的动态变化。所采用的实验和理论方法将为软物质物理和生物物理提供丰富的探索领域，为水凝胶领域确定令人兴奋的新方向，并导致新的生物材料的发现。

Proteins are bionanomachines. These workhorses of the cell are responsible for a vast array of biological functions. Acting in isolation or as part of larger, often complex machinery, they perform their function through structural and mechanical changes. Studies on the mechanical properties of proteins found in nature have provided much inspiration for the design of new materials that have a balance of advanced mechanical properties. This includes the remarkable combination of high mechanical strength, fracture toughness and elasticity in the giant muscle protein titin and the intriguing mechanical properties of natural silk fibres. Despite the apparent biological complexity of nature, studies have shown that proteins can be designed to successfully mimic the strength and passive elasticity of muscle. This has been achieved through the design of polyproteins, which contain a specific number and arrangement of protein domains. Polyproteins are important because they provide a clear mechanical fingerprint in experiments for monitoring the response of proteins to an applied mechanical force. Polyproteins can be described using polymer physics and can be manipulated using tools such as single molecule force spectroscopy (SMFS), which provides information on their mechanical stability and softness. The hierarchical structures and intermolecular interactions present in polyproteins and the networks they form present new opportunities. In particular, a recent exciting development is the use of polyproteins as building blocks in hydrogels. Hydrogels are three-dimensional, hydrated, highly porous, percolating polymer networks spanning macroscopic dimensions. The hydrogel field is now extensive, with considerable strengths in the UK. However, it is only very recently that polyprotein-based hydrogels can be explored, due to advances in a biological technique called recombinant DNA technology.Hydrogels composed of engineered polyproteins offer three key advantages (i) the modular design of the polyprotein chain can be used to mimic the attractive mechanical and structural hierarchy found in nature, (ii) folded globular proteins offer building blocks with sequence dependent and tuneable thermodynamic and mechanical properties, (iii) functionality is intrinsic to protein fold, allowing for the incorporation of specific biological recognition capabilities that respond to biomolecular cues. Polyprotein-based hydrogels are therefore an exciting, emerging area in soft matter and biophysics. The integral functionality of the folded protein offers huge opportunities for applications, such as tissue engineering and stem cell differentiation, as well as offering a route towards smart, responsive materials for micro-optics, biosensors, and controlled release for drugs. While tools exist for measuring the structure, dynamics and mechanics of both proteins and of hydrogels, little is known about how this information translates between the nano- and mesoscopic length scales. A systematic and rational approach to hydrogel design requires the mechanical and structural properties of the system to be understood at all levels of hierarchical organisation. This fellowship will deliver a platform for the production of polyprotein hydrogels that possess specific biological function capabilities, enabling dynamic changes in mechanical and structural properties in response to biomolecular cues. The experimental and theoretical methods employed will provide a rich area for exploration in soft matter physics and biophysics, define exciting new directions in the hydrogel field, and lead to the discovery of novel biomaterials for exploitation.