42 | December 2021 www.facs.website Kousuke Tsuchiya Kousuke Tsuchiya received his Ph.D. in polymer chemistry in 2007 from the Tokyo Institute of Technology after engaging in the synthesis of functional polymers under the supervision of Prof. Mitsuru Ueda. He then was appointed an assistant professor at the Tokyo University of Agriculture and Technology, where he worked on the development of functional polymeric materials for optic and electronic devices. In 2015, he began conducting more biochemical research at the RIKEN Center for Sustainable Resource Science as a senior research scientist. He currently engages a project associate professor at the Kyoto University. His current work focuses on sustainable syntheses of bio-based polymers including polypeptides, and he has been recognized by awards such as Award for Encouragement of Research in Polymer Science from the Society of Polymer Science, Japan, and Polymer Chemistry Emerging Investigator 2020 from the Royal Society of Chemistry. Keiji Numata Keiji Numata is currently Full Professor at Department of Material Chemistry, Kyoto University, and Team Leader at the Biomacromolecules Research Team, RIKEN Center for Sustainable Resource Science, Japan. He is also Research Director for JST-ERATO Numata Organellar Reaction Cluster Project and leads the Precision Polymer Degradation, Grant-inAid for Transformative Research Area, in Japan. He investigates biosynthesis and material design of structural proteins, polypeptide, and poly(amino acid). He previously worked as JSPS Postdoctoral Fellow for Research Abroad at Tufts University (Medford, MA, United States), where he studied biosynthesis of silk-based polymers via bacterial pathways, as well as biomedical application of silk-based polymers. Dr. Numata has received numerous awards for his work and is currently one of the associate editors of ACS Biomaterials Science and Engineering. Green synthesis catalyzed by proteases Renewable polymeric materials produced from natural bioresources are fascinating alternatives to chemical products derived from petroleum that can fulfill the needs of future sustainable societies. Biodegradability and/ or recyclability are key features for the development of sustainable materials to meet this requirement. The United Nations (UN) adopted 17 sustainable development goals (SDGs) in 2015 to achieve sustainable development by 2030. These SDGs aim to tackle an urgent call for action by all countries in a global partnership, and most of them relate to environmental issues. To realize these criteria, developing an environmentally benign manufacturing process and producing novel biobased polymeric materials to replace petroleum-based materials are inevitably important. Various biopolymers derived from natural resources, such as poly(lactic acid), polyhydroxyalkanoate, and cellulose, have extensively been applied to practical use in commercial products. Polypeptides are another attractive biopolymer in terms of versatility in the molecular design of amino acid sequences. A rational choice of amino acid residues in polypeptide sequences offers a desired functionality. Polypeptides are conventionally prepared by chemical synthesis, such as solid phase peptide synthesis and ring-opening polymerization of amino acid N-carboxyanhydride (NCA), or biosynthesis in host microbes as a form of protein, which generally suffers from tedious purification steps. We have pursued ideal synthetic methods for functional biopolymers, including polypeptides, through engineered pathways utilizing natural machinery. Enzymatic synthesis of polypeptides, named chemoenzymatic polymerization, can be used to build peptide bonds with the aid of proteases, which naturally cleave the peptide bonds in proteins (Figure 1). An appropriate combination of proteases and amino acid monomers enables us to synthesize various types of polypeptides.1-2 Chemoenzymatic polymerization possesses tremendous advantages over traditional synthetic methods. The polymerization, which generally involves just mixing amino acid monomers with a protease, proceeds in aqueous buffer solutions instead of organic solvents. Because of the substrate specificity of proteases, the resulting polypeptides have regio- and stereoselectively well-defined structures. The leaving group is only a small alcohol molecule such as ethanol during polymerization, which can achieve excellent atom economy compared with conventional chemical syntheses using condensing agents. Collectively, chemoenzymatic polymerization offers green, facile synthesis of polypeptides with distinct structures. We have previously polymerized a variety of amino acid monomers, mostly in ester forms, via chemoenzymatic polymerization to provide polypeptides with a wide range of functional groups. In addition to amino acid monomers, oligopeptide ester derivatives are also candidate materials for polymerizable monomers. Di- or tripeptides with appropriate From Structural to Functional Materials: a Green Way to Produce Functional Biopolymers Based on Polypeptides
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