In nature, high-performance biological polymers and composites consist of various organisms. The high-performance biopolymers are mainly protein/polypeptide, and have 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 in RIKEN has successfully synthesized various polypeptides, even with unnatural amino acids or nylon units, via chemo-enzymatic polymerization (ACS Catal 2016, Chem Commun 2017, Polym Chem 2017). Those artificial polypeptides containing unnatural units achieve several properties that cannot be done by natural polypeptides. This synthesis method provides a new insight for material design of polypeptide. Novel multiblock polypeptides with a structure similar to the unique sequence observed in spider silk proteins were synthesized via a two-step chemical and enzymatic synthesis method (ACS Macro Let 2017). Two types of polypeptide fragments were prepared by chemoenzymatic polymerization: polyalanine as a hard block, which forms beta-sheets in the spider silk fibers, and poly(glycine-random-leucine) as a soft block. These two fragments were ligated by post-polycondensation using polyphosphoric acid as a condensing agent. Resulting multiblock polypeptides formed an antiparallel beta-sheet structure with a degree of crystallinity similar to that of spider silk, which resulted in a fibrous morphology. Similar to the silk-like polypeptides, elastin-like polypeptides were also synthesized (Polym Chem 2018). We also reported the new finding in spider silk spinning (Biomacromolecules 2017, Nat Commun 2018, Biomacromolecules 2018), which is important to design tough structural polymers. Based on the natural systems and hierarchical structures, we investigate various biological and eco-friendly polymers and materials.

Rationally-designed polypeptides based on structural proteins

2019 Fall National Meeting

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