Hierarchical Protein Assemblies as a Basis for Materials
Nature produces a wide range of fibrous biopolymers with interesting mechanical properties that compare with the best man‐made polymer fibres. Several of these biopolymer fibres are almost entirely composed of proteins, which have self‐assembled to a hierarchical structure that in some case does not contain any chemical but only physical cross‐linking. Therein, at several different length scales from the molecule to the macroscopic scale there is order or structure imposed onto the components of the material. These structural hierarchies in the material impart its physical properties allowing it to fulfil its natural role or function. Understanding hierarchically structured proteins is a basis to create systems of new materials that either mimic the entire natural material or cherry‐pick the features that impart the specific function one desires in order to apply it to man‐made materials. In this chapter we will discuss hierarchical structures of fibrous proteins starting with the simplest, those with only one or a couple of structural levels, which tend to be formed from single proteins. We will then go to a higher level of complexity, those fibres that incorporate two or more proteins within their structure. These have more varied conformations and can incorporate multiple structural proteins, or a single structural protein with one or more chaperone like proteins that help in the assembly or stabilisation of the solution from which the fibre is formed such as in Lepidoptera silk. We will lastly go on to describe those threads that are multi‐component materials incorporating two or more basic fibres that are fundamental to the integrity of the material, or incorporate multiple different materials such as cell remnants.