Unravelling the secrets of silk: an in-depth biochemical analysis of spider and silkworm silk

Silk is a protein-based biopolymer produced by many different invertebrate species from amphipods to spiders. Its incredible material properties, biocompatibility and antimicrobial properties make it one of the most desirable natural fibres in the race for new materials, with major potential impacts in everything from biomedical research to its aerospace applications. Although silk has been studied in detail since the latter part of the 20th century the field is still unable to produce truly comparable synthetics due to the complexity of biological factors involved in influencing silks properties. The major focus of this thesis is examining biological and structural factors that impact silk properties within spiders and silkworms. To examine this, I analysed silk across many scales from phylogenetic trends in amino acid composition and material properties, down to the Nano-scale examining the impacts of molecular structure, pioneering new methods of silk analysis through utilisation of dynamic nuclear polarization (DNP) solid-state nuclear magnetic resonance (ssNMR) spectroscopy. Using a comparative meta-analysis, I found that within spiders MaSp composition is a major influencing factor broadly across phylogeny and that glycine and serine concentration have a more influential impact than previously thought, whilst confirming the importance of proline in influencing silks elastic properties. I explore the inconsistency and spread of isotopically labelled alanine within spider’s silk and further our understanding of metabolic pathways into silk proteins and silk structure. I then provide and examine the efficacy of an alternative to isotopic labelling, DNP ssNMR, which reveals unprecedented detail into silks molecular structure, boasting a > 50 fold signal enhancement allowing determination of the structural role of lower abundance amino acids like arginine and revealing the presence of the first known example of a post-translational modified amino acid hydroxyproline within silk. lastly, I explore the major implications of hitherto undocumented voids found within native silkworm silks, the molecular structural influences that help create them, their impact on mechanical property measurements and potential development and utilisation ecologically improving the insulative properties of their cocoons. Ultimately, whilst revealing invaluable new information and methods for the silk field to help it towards its goal of producing comparable bio-mimetics, this thesis highlights the need for a biologically minded and holistic study of biomaterials such as silk to understand all the factors that help organisms achieve such incredible and complex materials