www.asiachem.news December 2021 | 47 residue into the sequence of CPP because it is known to strongly induce helix structures. Novel periodic peptides were synthesized by the chemoenzymatic polymerization of tripeptide esters containing cationic lysine and Aib residues.20 The resulting peptide with a repetitive sequence of the LysAibAla motif, designated the KAibA peptide, exhibited not only excellent membrane permeability but also long-term stability in plant cells compared with conventional amphiphilic or cationic CPPs. The KAibA peptide was applicable to various plants from model plants such as A. thaliana and tobacco (Nicotiana benthamiana) and crops such as rice (Oryza sativa) to practical plants such as kenaf (Hibiscus cannabinus, a fast-growing tall plant offering highstrength fibers) regardless of the type of tissue, including leaves and calli. Plant cells, unlike animal cells, have a cell wall in addition to a cell membrane. Cell walls are a relatively rigid tissue with hierarchical, dense network structures consisting mainly of cellulose and other polysaccharides, such as hemicellulose and pectin.21-22 Therefore, in contrast to cell membranes with dynamic lipid-layered structures, cell walls afford a major physical barrier for the transport of materials into plant cells. We focused on the cellulose network in cell walls and attempted to dissociate the network to maximize the penetration efficiency of the peptide/DNA complex through the cell wall. Cellulose, which suffers from poor processability due to its low solubility and nonmelting property, is known to dissolve in certain ionic liquids. Imidazolium-type ionic liquids with high hydrogen bond accepting ability interact and cleave the intermolecular hydrogen bonds of cellulose, resulting in complete dissolution of cellulose. We introduced such an imidazolium zwitterion structure similar to cellulose-dissolving ionic liquids into periodic polypeptides via chemoenzymatic polymerization (Figure 7).23 A tripeptide ester consisting of histidine flanked with glycine residues was polymerized in the presence of papain, and imidazole side groups of the resulting periodic polypeptide were converted to a zwitterionic structure. Based on in vitro experiments, bundles of cellulose nanocrystals derived from tunicates are found to be dissociated into smaller cellulose crystallites by treatment with zwitterionic polypeptides under mild conditions. Cultured tobacco plant cells (BY-2 cells) were also treated with zwitterionic polypeptides to investigate the effect of the polypeptide on the cellulose network in the cell wall. The zwitterionic polypeptide interacts with both the cellulose network and the amorphous pectin layers of BY-2 cells at a low polypeptide concentration, which leads to the formation of large pores. Compared with the ionic liquid that dissolves cellulose, zwitterionic polypeptide shows almost no cytotoxicity at the efficacious concentration. We are trying to improve the material delivery efficiency into plant cells using such a novel “cell-wall permeable peptide” that helps polypeptide carriers penetrate cell walls. Conclusion Based on multifaceted approaches to produce polypeptide materials, we have developed protease-catalyzed green synthesis of polypeptide materials.24 Designing suitable amino acid sequences to construct specific secondary to higher-order structures that provide desired functionality allows us to synthesize various polypeptides that are expected to be widely applicable ranging from structural to functional materials. A simple protocol for chemoenzymatic polymerization leads to cost-effective, large-scale production of functional polypeptide materials. Ecofriendly chemical synthesis using enzymes has huge potential to replace the existing materials derived from exhaustible resources. From the perspective of energy reduction, enzymatic synthesis will also contribute to sustainable material production because it proceeds at mild temperatures. Our goal is to establish an innovative material manufacturing system that enables carbon-neutral cycles for a sustainable society. The novel synthetic method based on chemoenzymatic polymerization will be a key technology that plays an important role in the material ecocycle system. Recent advancements using enzyme-utilized synthesis will shed light on the potential for innovative materials based on polypeptides. ◆ References 1. Tsuchiya, K.; Miyagi, Y.; Miyamoto, T.; Gudeangadi, P. G.; Numata, K., Synthesis of Polypeptides. In Enzymatic Polymerization towards Green Polymer Chemistry, Kobayashi, S.; Uyama, H.; Kadokawa, J., Eds. Springer Singapore: Singapore, 2019; pp 233-265. 2. 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