Understanding, engineering and exploiting protein self-assembly.

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This NSERC-funded research program focuses on developing an atomic-level understanding of how spider silks, a type of protein, are able to form larger structures such as fibres and particles. Beyond expanding understanding of these poorly understood formation processes, the long-term goal of these studies is the engineering of proteins specifically tailored to a desired form. This provides an outstanding potential range of materials for biotechnological use. Spider aciniform silk is a protein fibre used by spiders to wrap their prey. It is one of the toughest known materials, meaning that it can absorb more energy prior to breaking than almost any other material. The more widely-studied spider dragline silk, in contrast, can withstand heavier loads but is not as flexible, giving a lower toughness. Harvesting of silk from spiders is not a feasible route to obtain sufficient amounts of material for applied uses. We have developed a method to use bacteria to produce this silk. This has allows us to readily modify the individual amino acids making up the protein and to label the protein to allow modern nuclear magnetic resonance (NMR) spectroscopy experiments. To date, we have bacterially produced a variety of recombinant aciniform silk proteins, developed methods to produce fibres with a diameter ~10% that of human hair and >1 km in length, and have formed tiny silk particles ("nanoparticles") that can be loaded with different chemicals. These silk fibres have significant potential for application in a wide variety of areas given their outstanding toughness. Alternatively, our silk nanoparticles are potentially applicable for drug delivery or crop protection applications. For each form of silk protein, we use NMR spectroscopy to pinpoint the locations of individual atoms. This has allowed us to determine the atomic-level structure of aciniform silk in solution. We can also monitor specific changes to atomic positions and motion during the transition from the soluble state to the fibrous state. As we do so, we monitor the types and properties of fibres or nanoparticles that are formed using atomic force and electron microscopy. We also apply tensile testing methods to determine strength and toughness. Comparison of the atomic arrangement to mechanical properties as a function of changes in amino acids allows us to engineer new forms of silk based upon acinform silk but incorporating specific, desirable properties. Beyond these scientific and materials outcomes, this DG-funded work allows highly qualified personnel from undergraduate through postdoctoral researchers to become expert in techniques to: (1) bacterially produce proteins; (2) characterize the atomic-level behaviour of proteins in soluble states, nanoparticles, and silk fibres; (3) spin silk proteins into fibres; (4) characterize fibre and particle appearance and mechanics; and, (5) engineer proteins with desired chemical properties.