Understanding the Native Spider Silk Spinning Process Using Recombinant Silk Proteins

Spider silks are a biological protein polymer with an incredibly diverse range of mechanical properties and functions. Spider silk has been recognized as having mechanical properties that rival man-made materials, fueling attempts to make synthetic versions. However, there have been only a few examples of synthetic silks meeting or surpassing natively-spin materials to date - none of which have been successfully commercialized. This is likely due to the numerous factors working in concert at length scales between the atomic and macroscale to create a continuous fiber with native-like properties. The goal of the research presented in this dissertation is to improve our understanding of the fiber spinning process at these length scales and to understand the material properties of the resulting fibers. These processes were studied using advanced liquid and solid-state nuclear magnetic resonance spectroscopy techniques, solid-phase peptide synthesis, molecular dynamics simulations, dynamic light scattering, and electron microscopy on native and recombinant silk proteins in solution and as fibers. In Chapter 2, we investigate the atomic and mesoscale interactions that facilitate spider silk pre-assemblies and find that dragline silk proteins in 4 M urea show the greatest deviation from glandular conditions at the peripheral ends of the poly(Ala) motifs. These proteins also display a critical aggregation concentration near 4 wt% in 4 M urea. In Chapter 3, we utilize molecular dynamics (MD) simulations to assist in developing a more accurate structural depiction of a native-sized spider silk proteins in solution, and find consistent residues located on the surface of the simulated structure which may help to drive pre-assembly formation. In Chapter 4, we synthesize peptide mimics to study the hierarchical pre-assembly of native silk proteins and show that sequences taken from the amorphous region of dragline silks are capable of hierarchical structure formation and liquid-liquid phase separation. In Chapter 5, we discuss our results from a collaboration with Prof. Thomas Scheibel’s Lab at the University of Bayreuth in Germany where we investigate the secondary structure of isotopically-labeled recombinant silk as concentrated dopes and fibers. In Chapters 6 and 7, we discuss a novel silk used during prey wrapping that is capable of crosslinking when wetted with water, where the as-spun mainly α-helical, coiled-coil silk transitions to having increased ß-sheet character with matted morphology following water treatment