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. 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. 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. We synthesized polypeptides that consist of di- and tri-peptide motifs containing proline and valine via chemoenzymatic polymerization. Di- and tri-peptide ethyl esters (ValGly-OEt, GlyProGly-OEt, and ValProGly-OEt) could be polymerized by papain. The copolymer of ValProGly-OEt and ValGly-OEt, poly(ValProGly-<i>co</i>-ValGly), which was composed of a repetitive sequence of elastin, exhibited a temperature-dependent structural transition similar to tropoelastin. The post-polycondensation product of poly(ValProGly-<i>co</i>-ValGly) showed higher molecular weight and elastin-like thermal behaviors. These works provide new examples of synthetic multiblock polypeptides mimicking the natural structural proteins as renewable materials.

Chemo-enzymatic synthesis of silk and elastin-like polypeptides as renewable materials

256th National Meeting (2018)

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