Papain-Catalyzed Chemoenzymatic Synthesis of Telechelic Polypeptides Using Bis(Leucine Ethyl Ester) Initiator

Chemoenzymatic Polymerization of l-Serine Ethyl Ester in Aqueous Media without Side-Group Protection

Poly(l-serine) (polySer) has tremendous potential as a polypeptide-based functional material due to the utility of the hydroxyl group on its side chain; however, tedious protection/deprotection of the hydroxyl groups is required for its synthesis. In this study, polySer was synthesized by the chemoenzymatic polymerization (CEP) of l-serine ethyl ester (Ser-OEt) or l-serine methyl ester (Ser-OMe) using papain as a catalyst in an aqueous medium. The CEP of Ser-OEt proceeded at basic pH ranging from 7.5 to 9.5 and resulted in the maximum precipitate yield of polySer at an optimized pH of 8.5. A series of peaks detected by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry revealed that the formed precipitate consisted of polySer with a degree of polymerization ranging from 5 to 22. Moreover, infrared spectroscopy, circular dichroism spectroscopy, and synchrotron wide-angle X-ray diffraction measurements indicated that the obtained polySer formed a β-sheet/strand structure. This is the first time the synthesis of polySer was realized by CEP in aqueous solution without protecting the hydroxyl group of the Ser monomer.

A silk composite fiber reinforced by telechelic-type polyalanine and its strengthening mechanism

A telechelic-type polyalanine was doped in silkworm silk fibroins to prepare reinforced composite fibers, which exhibited 42% and 51% higher mechanical properties than silk-only fibers in terms of tensile strength and toughness, respectively.

Amino acid derived biopolymers: Recent advances and biomedical applications

Over the past few years, amino acids (AA) have emerged as promising biomaterials for the synthesis of functional polymers. Owing to the diversity of functional groups in amino acids, various polymerization methods may be used to make a wide range of well-defined functional amino-acid/peptide-based optically active polymers with varying polymer lengths, compositions, and designs. When incorporated with chirality and self-assembly, they offer a wide range of applications and are particularly appealing in the field of drug delivery, tissue engineering, and biosensing. There are several classes of these polymers that include polyamides (PA), polyesters (PE), poly(ester-amide)s (PEA)s, polyurethanes (PU)s, poly(depsipeptide)s (PDP)s, etc. They offer the ability to control functionality, conjugation, crosslinking, stimuli responsiveness, and tuneable mechanical/thermal properties. In this review, we present the recent advancements in the synthesis strategies for obtaining these amino acid-derived bio-macromolecules, their self-assembly properties, and the wealth of prevalent applications.

Peptide-Based Polyion Complex Vesicles That Deliver Enzymes into Intact Plants To Provide Antibiotic Resistance without Genetic Modification

Direct delivery of enzymes into intact plants using cell-penetrating peptides (CPPs) is an attractive approach for modifying plant functions without genetic modification. However, by conventional methods, it is difficult to maintain the enzyme activity for a long time because of proteolysis of the enzymes under physiological conditions. Here, we developed a novel enzyme delivery system using polyion complex vesicles (PICsomes) to protect the enzyme from proteases. We created PICsome-bearing reactive groups at the surface by mixing an anionic block copolymer, alkyne-TEG-P(Lys-COOH), and a cationic peptide, P(Lys). The PICsome encapsulated neomycin phosphotransferase II (NPTII), a kanamycin resistance enzyme, and protected NPTII from proteases in vitro. A CPP-modified PICsome delivered NPTII into the root hair cells of Arabidopsis thaliana seedlings and provided kanamycin resistance in the seedlings that lasted for 7 days. Thus, the PICsome-mediated enzyme delivery system is a promising method for imparting long-term transient traits to plants without genetic modification.

Self-Assembly-Assisted Kinetically Controlled Papain-Catalyzed Formation of mPEG-b-Phe(Leu)x

Self-assembling peptide materials are promising next-generation materials with applications that include tissue engineering scaffolds, drug delivery, bionanomedicine, and enviro-responsive materials. Despite these advances, synthetic methods to form peptides and peptide-polymer conjugates still largely rely on solid-phase peptide synthesis (SPPS) and N-carboxyanhydride ring-opening polymerization (NCA-ROP), while green methods remain largely undeveloped. This work demonstrates a protease-catalyzed peptide synthesis (PCPS) capable of directly grafting leucine ethyl ester (Leu-OEt) from the C-terminus of a methoxy poly(ethylene glycol)-phenylalanine ethyl ester macroinitiator in a one-pot, aqueous reaction. By using the natural tendency of the growing hydrophobic peptide segment to self-assemble, a large narrowing of the (Leu)_x distributions for both mPEG₄₅-b-Phe(Leu)_x and oligo(Leu)_x coproducts, relative to oligo(Leu)_x synthesized in the absence of a macroinitiator (mPEG₄₅-Phe-OEt), was achieved. A mechanism is described where in situ β-sheet coassembly of mPEG₄₅-b-Phe(Leu)_x and oligo(Leu)_x coproducts during polymerization prevents peptide hydrolysis, providing a means to control the degree of polymerization (DP) and dispersity of diblock (Leu)_x segments (matrix-assisted laser desorption time-of-flight (MALDI-TOF) x = 5.1, dispersity ≤ 1.02). The use of self-assembly to control the uniformity of peptides synthesized by PCPS paves the way for precise peptide block copolymer architectures with various polymer backbones and amino acid compositions synthesized by a green process.

Facile terminal functionalization of peptides by protease-catalyzed chemoenzymatic polymerization toward synthesis of polymeric architectures consisting of peptides

Terminal functionalized polypeptides were synthesized in one-pot chemoenzymatic polymerization using protease for constructing special polymeric architectures.

Poly(alanine-nylon-alanine) as a bioplastic: chemoenzymatic synthesis, thermal properties and biological degradation effects

Poly(amino acids) such as polypeptides and proteins are attractive biomass-based polymers that potentially contribute to circular economy for plastic.

A covalently crosslinked silk fibroin hydrogel using enzymatic oxidation and chemoenzymatically synthesized copolypeptide crosslinkers consisting of a GPG tripeptide motif and tyrosine: control of gelation and resilience

A covalently crosslinked silk fibroin hydrogel was successfully formedviaan enzymatic crosslinking reaction using copolypeptides, which consist of a glycine–proline–glycine tripeptide motif and tyrosine, as linker molecules.

Insights into the Stereospecificity in Papain-Mediated Chemoenzymatic Polymerization from Quantum Mechanics/Molecular Mechanics Simulations

Chemoenzymatic peptide synthesis is an efficient and clean method to generate polypeptides for new applications in the fields of biomedical and functional materials. However, this enzyme-mediated synthesis is dependent on the reaction rate of the protease biocatalyst, which is essentially determined by the natural substrate specificity of the enzyme. Papain, one of the most studied cysteine proteases, is extensively used for the chemoenzymatic synthesis of new polypeptides. Similar to most proteases, papain displays high stereospecificity toward l-amino acids, with limited reactivity for the d-stereoisomer counterparts. However, the incorporation of d-amino acids into peptides is a promising approach to increase their biostability by conferring intrinsic resistance to proteolysis. Herein, we determined the stereospecific-limiting step of the papain-mediated polymerization reaction with the chiral substrates l/d-alanine ethyl ester (Ala-OEt). Afterward, we used Quantum Mechanics/Molecular Mechanics (QM/MM) simulations to study the catalytic mechanism at atomic level of detail and investigate the origin of its stereospecificity. The experimental and computational results show that papain is able to attack both l- and d-stereoisomers of Ala-OEt, forming an enzyme-substrate intermediate, and that the two reactions display a similar activation barrier. Moreover, we found that the reduced catalytic activity of papain in the polymerization of d-amino acids arises from the aminolysis step of the reaction, in which l-Ala-OEt displays a significantly lower free-energy barrier (12 kcal/mol) than d-Ala-OEt (30 kcal/mol). Further simulations suggest that the main factor affecting the polymerization of d-amino acids is the configuration of the d-acyl-intermediate enzyme, and in particular the orientation of its methyl group, which hinders the nucleophilic attack by other monomers and thus the formation of polypeptides.

Chemoenzymatic synthesis of polypeptides containing the unnatural amino acid 2-aminoisobutyric acid

Polypeptides containing 2-aminoisobutyric acid (Aib) units as an unnatural amino acid residue were synthesized by papain-catalyzed chemoenzymatic polymerization of a tripeptide ethyl ester l-Ala-Aib-l-Ala-OEt in an aqueous medium. The Aib-containing polypeptide adopted an α-helix conformation in both the solid and solution phases, which was induced by the periodic Aib residue.

Spider dragline silk composite films doped with linear and telechelic polyalanine: Effect of polyalanine on the structure and mechanical properties

Spider dragline silks have attracted intensive attention as eco-friendly tough materials because of their excellent mechanical property and biomass-based origin. Composite films based on a recombinant spider dragline silk protein (ADF3) from Araneus diadematus were prepared by doping with linear or telechelic poly(L-alanine) (L- or T-polyA, respectively) as a reinforcing agent. Higher tensile strength and toughness of the composite films were achieved with the addition of polyA compared with the tensile strength and toughness of the silk-only film. The difference in the reinforcing behavior between L- and T-polyA was associated with their primary structures, which were revealed by wide angle X-ray diffraction analysis. L-polyA showed a tendency to aggregate in the composite films and induce crystallization of the inherent silk β-sheet to afford rigid but brittle films. By contrast, T-polyA dispersion in the composite films led to the formation of β-sheet crystal of both T-polyA and the inherent silk, which imparted high strength and toughness to the silk films.

Chemoenzymatic synthesis of polypeptides consisting of periodic di- and tri-peptide motifs similar to elastin

Elastin-like polypeptides containing proline were synthesized via chemoenzymatic polymerization and exhibited a temperature-dependent structural transition.

Chemoenzymatic Synthesis of Polypeptides for Use as Functional and Structural Materials

Polypeptides inspired by the natural functional and structural proteins present in living systems are promising materials for various fields in terms of their versatile functionality and physical properties. Designing and synthesizing mimetic sequences of specific peptide motifs in proteins are important for exploring the functionality of natural proteins. Chemoenzymatic polymerization, which utilizes aminolysis (i.e., the reverse reaction of hydrolysis catalyzed by proteases), is a useful technique for synthesizing artificial polypeptide materials and has several advantages, including facile synthesis protocols, environmental friendliness, scalability, and atom economy. In this review, recent progress in chemoenzymatic polypeptide synthesis for the production of functional and structural materials for various applications is summarized in conjunction with the current status of technical challenges in the field.

Papain-Catalyzed Synthesis of Polyglutamate Containing a Nylon Monomer Unit

Peptides have the potential to serve as an alternative for petroleum-based polymers to support a sustainable society. However, they lack thermoplasticity, owing to their strong intermolecular interactions. In contrast, nylon is famous for its thermoplasticity and chemical resistance. Here, we synthesized peptides containing a nylon unit to modify their thermal properties by using papain-catalyzed chemoenzymatic polymerization. We used l-glutamic acid alkyl ester as the amino acid monomer and nylon 1, 3, 4, and 6 alkyl esters as the nylon unit. Papain catalyzed the copolymerization of glutamic acid with nylon 3, 4, and 6 alkyl esters, whereas the nylon 1 unit could not be copolymerized. Other proteases used in this study, namely, bromelain, proteinase K, and Candida antarctica lipase (CALB), were not able to copolymerize with any nylon units. The broad substrate specificity of papain enabled the copolymerization of l-glutamic acid with a nylon unit. The peptides with nylon units demonstrated different thermal profiles from that of oligo(l-glutamic acid). Therefore, the resultant peptides with various nylon units are expected to form fewer intermolecular hydrogen bonds, thus altering their thermal properties. This finding is expected to broaden the applications of peptide materials and chemoenzymatic polymerization.