Tuesday, January 15, 2019
11:00 am

Special Mechanical and Civil Engineering Seminar

Polypeptides as Biological Structural Materials
Keiji Numata, RIKEN Center for Sustainable Resource Science

High-performance biological materials in nature are mainly composed of amino acids.  Polymer of amino acids, namely, polypeptide has therefore been recognized as bioactive and functional material, however, use of those biopolymers as structural materials is still challenging. One of the major drawbacks of polypeptide-based materials is their limited synthesis method. My research group has successfully synthesized various polypeptides, even with unnatural amino acids or nylon units, via chemo-enzymatic polymerization. Those artificial polypeptides containing unnatural units achieve several properties that cannot be done by natural polypeptides. With this polymerization method, my research group has reported spider silk-like and elastin-like polypeptides (ACS Macro Lett 2017. Polym. Chem. 2018). This synthesis method provides a new insight for material design of polypeptide.
My research group also focuses on spider silk dragline as a natural structural material. Although spider dragline is the toughest material, the spinning and formation mechanism has not been clarified until now. Many scientists and industrial researchers are trying to produce artificial silk materials with the same toughness as spider dragline, however, it has not been accomplished because of the mysterious spinning system. Despite the fact that the formation mechanism of silk fibers has been studied since the 19th century, the molecular mechanism and hierarchy of spider silk spinning are not clear yet. Recent advances in structural analysis technology have revealed that the structure of the N-terminal and C-terminal of spider silk contributes to the self-organization of the spinning process (Hang et al. Nature 2010). My research group also revealed the effect of the repetitive domain on the initial process of spinning, namely, from random coil to beta-sheet formation via polyproline II helix (Oktaviani et al. Nat. Commun. 2018). The transition from liquid to solid states makes difficult to understand and clear the molecular mechanisms behind it. Even before the fiber formation, intermolecular interactions involving two or more proteins with pH change, shear stress and dehydration have not been fully clarified and understood. Here, we aim to clarify the molecular mechanism of multiple silk proteins from single molecules up to tough fibers with hierarchical structure, which will establish a water-based sustainable spinning system to produce artificial tough fibers and materials. Furthermore, using polypeptide to modify plant organelles, we seek new biotechnology to modify and improve the physical properties of plant materials through a collaboration with plant scientists.

Contact Carolina Oseguera susta@caltech.edu at 626-395-4271
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