Ampholytic Peptides Consisting of an Alternating Lysine/Glutamic Acid Sequence for the Simultaneous Formation of Polyion Complex Vesicles.

Nanoarchitectures such as micelles and vesicles that self-assemble via electrostatic interactions between their charged polymeric components have been widely used as material delivery platforms. In this work, ampholytic peptides with a sequence of alternating lysine and glutamic acid residues were designed and synthesized via chemoenzymatic polymerization. This alternating sequence was achieved by trypsin-catalyzed polymerization of a dipeptide monomer. Due to the electrostatic interaction between the anionic and cationic residues, the prepared ampholytic peptides spontaneously formed nanosized assemblies with a size of 100-200 nm in water. Modification with tetra(ethylene glycol) (TEG) at the N-terminus of these ampholytic alternating peptides resulted in the formation of stable nanosized assemblies, while peptides consisting of random sequences of lysine and glutamic acid formed large aggregates with deteriorated stability even with TEG modification. Morphological observations using a field-emission scanning electron microscope and an atomic force microscope revealed that the obtained assemblies were spherical and hollow, indicating the spontaneous formation of vesicles from the TEG-modified ampholytic alternating peptides. These vesicles were able to encapsulate a model fluorescent protein within their hollow structures without structural collapse causing loss of fluorescence, demonstrating the potential of these nanocarriers for use in material delivery systems.

Regiocontrol of the Bulk Polymerization of Lysine Ethyl Ester by the Selection of Suitable Immobilized Enzyme Catalysts.

The development of a green and facile method for the controlled synthesis of functional polypeptides is desired for sustainable material applications. In this study, the regioselective synthesis of poly(l-lysine) (polyLys) via enzyme-catalyzed aminolysis was achieved by bulk polymerization of l-lysine ethyl ester (Lys-OEt) using immobilized Candida antarctica lipase Novozym 435 (IM-lipase) or trypsin (IM-trypsin). Structural characterization of the obtained polyLys revealed that IM-lipase resulted solely in ε-linked amide bond formation, whereas IM-trypsin predominantly provided α-linked polyLys. Optimization of the conditions for the bulk polymerization using immobilized enzymes resulted in high monomer conversion and a high degree of polymerization, with excellent regioselectivity. Molecular docking simulations revealed different binding conformations of Lys-OEt to the catalytic pockets of lipase and trypsin, which putatively resulted in different amino moieties being used for amide bond formation. The immobilized enzymes were recovered and recycled for bulk polymerization, and the initial activity was maintained in the case of IM-trypsin. The obtained α- and ε-linked polyLys products exhibited different degradability against proteolysis, demonstrating the possibility of versatile applications as sustainable materials. This enzymatic regioregular control enabled the synthesis of well-defined polypeptide-based materials with a diverging structural variety.

Replicating shear-mediated self-assembly of spider silk through microfluidics.

The development of artificial spider silk with properties similar to native silk has been a challenging task in materials science. In this study, we use a microfluidic device to create continuous fibers based on recombinant MaSp2 spidroin. The strategy incorporates ion-induced liquid-liquid phase separation, pH-driven fibrillation, and shear-dependent induction of ß-sheet formation. We find that a threshold shear stress of approximately 72 Pa is required for fiber formation, and that ß-sheet formation is dependent on the presence of polyalanine blocks in the repetitive sequence. The MaSp2 fiber formed has a ß-sheet content (29.2%) comparable to that of native dragline with a shear stress requirement of 111 Pa. Interestingly, the polyalanine blocks have limited influence on the occurrence of liquid-liquid phase separation and hierarchical structure. These results offer insights into the shear-induced crystallization and sequence-structure relationship of spider silk and have significant implications for the rational design of artificially spun fibers.

Plant Mitochondrial-Targeted Gene Delivery by Peptide/DNA Micelles Quantitatively Surface-Modified with Mitochondrial Targeting and Membrane-Penetrating Peptides.

Plant mitochondria play essential roles in metabolism and respiration. Recently, there has been growing interest in mitochondrial transformation for developing crops with commercially valuable traits, such as resistance to environmental stress and shorter fallow periods. Mitochondrial targeting and cell membrane penetration functions are crucial for improving the gene delivery efficiency of mitochondrial transformation. Here, we developed a peptide-based carrier, referred to as Cytcox/KAibA-Mic, that contains multifunctional peptides for efficient transfection into plant mitochondria. We quantified the mitochondrial targeting and cell membrane-penetrating peptide modification rates to control their functions. The modification rates were easily determined from high-performance liquid chromatography chromatograms. Additionally, the gene carrier size remained constant even when the mitochondrial targeting peptide modification rate was altered. Using this gene carrier, we can quantitatively investigate the relationships between various peptide modifications and transfection efficiency and optimize the gene carrier conditions for mitochondrial transfection.

Cell Wall-Denaturing Molecules for Plant Gene Modification.

Zwitterionic molecules, such as zwitterionic liquids (ZILs) and polypeptides (ZIPs), are attracting attention for application in new methods that can be used to loosen tight cell wall networks in a biocompatible manner. These novel methods can enhance the cell wall permeability of nanocarriers and increase their transfection efficiency into targeted subcellular organelles in plants. Herein, we provide an overview of the recent progress and future perspectives of such molecules that function as boosters for cell wall-penetrating nanocarriers.

1000 spider silkomes: Linking sequences to silk physical properties.

Spider silks are among the toughest known materials and thus provide models for renewable, biodegradable, and sustainable biopolymers. However, the entirety of their diversity still remains elusive, and silks that exceed the performance limits of industrial fibers are constantly being found. We obtained transcriptome assemblies from 1098 species of spiders to comprehensively catalog silk gene sequences and measured the mechanical, thermal, structural, and hydration properties of the dragline silks of 446 species. The combination of these silk protein genotype-phenotype data revealed essential contributions of multicomponent structures with major ampullate spidroin 1 to 3 paralogs in high-performance dragline silks and numerous amino acid motifs contributing to each of the measured properties. We hope that our global sampling, comprehensive testing, integrated analysis, and open data will provide a solid starting point for future biomaterial designs.

Relaxation of the Plant Cell Wall Barrier via Zwitterionic Liquid Pretreatment for Micelle-Complex-Mediated DNA Delivery to Specific Plant Organelles.

Targeted delivery of genes to specific plant organelles is a key challenge for fundamental plant science, plant bioengineering, and agronomic applications. Nanoscale carriers have attracted interest as a promising tool for organelle-targeted DNA delivery in plants. However, nanocarrier-mediated DNA delivery in plants is severely hampered by the barrier of the plant cell wall, resulting in insufficient delivery efficiency. Herein, we propose a unique strategy that synergistically combines a cell wall-loosening zwitterionic liquid (ZIL) with a peptide-displaying micelle complex for organelle-specific DNA delivery in plants. We demonstrated that ZIL pretreatment can enhance cell wall permeability without cytotoxicity, allowing micelle complexes to translocate across the cell wall and carry DNA cargo into specific plant organelles, such as nuclei and chloroplasts, with significantly augmented efficiency. Our work offers a novel concept to overcome the plant cell wall barrier for nanocarrier-mediated cargo delivery to specific organelles in living plants.

Polymer-coated carbon nanotube hybrids with functional peptides for gene delivery into plant mitochondria.

The delivery of genetic material into plants has been historically challenging due to the cell wall barrier, which blocks the passage of many biomolecules. Carbon nanotube-based delivery has emerged as a promising solution to this problem and has been shown to effectively deliver DNA and RNA into intact plants. Mitochondria are important targets due to their influence on agronomic traits, but delivery into this organelle has been limited to low efficiencies, restricting their potential in genetic engineering. This work describes the use of a carbon nanotube-polymer hybrid modified with functional peptides to deliver DNA into intact plant mitochondria with almost 30 times higher efficiency than existing methods. Genetic integration of a folate pathway gene in the mitochondria displays enhanced plant growth rates, suggesting its applications in metabolic engineering and the establishment of stable transformation in mitochondrial genomes. Furthermore, the flexibility of the polymer layer will also allow for the conjugation of other peptides and cargo targeting other organelles for broad applications in plant bioengineering.

Non-transgenic Gene Modulation via Spray Delivery of Nucleic Acid/Peptide Complexes into Plant Nuclei and Chloroplasts.

Genetic engineering of economically important traits in plants is an effective way to improve global welfare. However, introducing foreign DNA molecules into plant genomes to create genetically engineered plants not only requires a lengthy testing period and high developmental costs but also is not well-accepted by the public due to safety concerns about its effects on human and animal health and the environment. Here, we present a high-throughput nucleic acids delivery platform for plants using peptide nanocarriers applied to the leaf surface by spraying. The translocation of sub-micrometer-scale nucleic acid/peptide complexes upon spraying varied depending on the physicochemical characteristics of the peptides and was controlled by a stomata-dependent-uptake mechanism in plant cells. We observed efficient delivery of DNA molecules into plants using cell-penetrating peptide (CPP)-based foliar spraying. Moreover, using foliar spraying, we successfully performed gene silencing by introducing small interfering RNA molecules in plant nuclei via siRNA-CPP complexes and, more importantly, in chloroplasts via our CPP/chloroplast-targeting peptide-mediated delivery system. This technology enables effective nontransgenic engineering of economically important plant traits in agricultural systems.

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 ß-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.

Endosome-escaping micelle complexes dually equipped with cell-penetrating and endosome-disrupting peptides for efficient DNA delivery into intact plants.

The delivery of DNA to plants is crucial for enhancing their ability to produce valuable compounds and adapt to climate change. Peptides can provide a versatile tool for delivering DNA to a specific target organelle in various plant species without the use of specialized equipment. However, peptide-mediated DNA delivery suffers from endosomal entrapment and subsequent vacuolar degradation of the DNA cargo, which leads to poor transfection efficiency. To overcome the lack of a reliable approach for bypassing vacuolar degradation in plants, we herein present an endosome-escaping micelle. The micelle surface is dually modified with cell-penetrating (CPP) and endosome-disrupting peptides (EDP) and the core is composed of plasmid DNA condensed with cationic peptides. Due to the functions of CPP and EDP, the dual peptide-modified micelles efficiently undergo endocytic internalization and escape from endosomes to the cytosol, thereby achieving significantly enhanced transfection of intact plants with negligible cytotoxicity. The present study offers a robust strategy for efficient intracellular DNA delivery to plants without vacuolar degradation, and can facilitate plant bioengineering for diverse biotechnological applications.

Synthetic Mitochondria-Targeting Peptides Incorporating α-Aminoisobutyric Acid with a Stable Amphiphilic Helix Conformation in Plant Cells.

In the genetic modification of plant cells, the mitochondrion is an important target in addition to the nucleus and plastid. However, gene delivery into the mitochondria of plant cells has yet to be established by conventional methods, such as particle bombardment, because of the small size and high mobility of mitochondria. To develop an efficient mitochondria-targeting signal (MTS) that functions in plant cells, we designed the artificial peptide (LURL)3 and its analogues, which periodically feature hydrophobic α-aminoisobutyric acid (Aib, U) and cationic arginine (R), considering the consensus motif recognized by the mitochondrial import receptor Tom20. Circular dichroism measurements and molecular dynamics simulation studies revealed that (LURL)3 had a propensity to form a stable α-helix in 0.1 M phosphate buffer solution containing 1.0 wt % sodium dodecyl sulfate. After internalization into plant cells via particle bombardment, (LURL)3 revealed highly selective accumulation in the mitochondria, whereas its analogue (LARL)3 was predominantly located in the vacuoles in addition to mitochondria. The high selectivity of (LURL)3 can be attributed to the incorporation of Aib, which promotes the hydrophobic interaction between the MTS and Tom20 by increasing the hydrophobicity and helicity of (LURL)3. The present study provided a prospective mitochondrial targeting system using the simple design of artificial peptides.

Crystallization-induced mechanofluorescence for visualization of polymer crystallization.

The growth of lamellar crystals has been studied in particular for spherulites in polymeric materials. Even though such spherulitic structures and their growth are of crucial importance for the mechanical and optical properties of the resulting polymeric materials, several issues regarding the residual stress remain unresolved in the wider context of crystal growth. To gain further insight into micro-mechanical forces during the crystallization process of lamellar crystals in polymeric materials, herein, we introduce tetraarylsuccinonitrile (TASN), which generates relatively stable radicals with yellow fluorescence upon homolytic cleavage at the central C-C bond in response to mechanical stress, into crystalline polymers. The obtained crystalline polymers with TASN at the center of the polymer chain allow not only to visualize the stress arising from micro-mechanical forces during polymer crystallization via fluorescence microscopy but also to evaluate the micro-mechanical forces upon growing polymer lamellar crystals by electron paramagnetic resonance, which is able to detect the radicals generated during polymer crystallization.

All-Peptide-Based Polyion Complex Vesicles: Facile Preparation and Encapsulation of the Protein in Active Form.

The polyion complex vesicle (PICsome) is a promising platform for bioactive molecule delivery as well as nanoreactor systems. In addition to anionic and cationic charged blocks, a hydrophilic poly(ethylene glycol) (PEG) block is mostly employed for PICsome formation; however, the long-term safety of the PEG component in vivo is yet to be clarified. In this study, we developed novel PEG-free PICsome comprising all peptide components. Instead of the PEG block, we selected the sarcosine (Sar) oligomer as a hydrophilic block and fused it with anionic oligo(l-glutamic acid). Mixing the Sar-containing anionic peptide with cationic oligo(l-lysine) resulted in the formation of stable vesicles. The peptide-based PICsome was able to encapsulate a model protein in its hollow structure. After modification of the surface with a cell-penetrating peptide, the protein-encapsulated PICsome was successfully delivered into plant cells, indicating its promised for application as a biocompatible carrier for protein delivery.

Visualization of the Necking Initiation and Propagation Processes during Uniaxial Tensile Deformation of Crystalline Polymer Films via the Generation of Fluorescent Radicals.

To visualize and simultaneously quantify the necking behavior of crystalline polymer films during uniaxial stretching, tetraarylsuccinonitrile (TASN) moieties were introduced into polymers at the center of the main chain. TASN can produce a relatively stable radical that emits yellow fluorescence in response to mechanical stress. During the uniaxial elongation test of the TASN-centered crystalline polymers, the yellow fluorescence derived from the dissociated TASN radicals was used for microscale observations that showed the orientation of the polymer chains in the stretching direction. Furthermore, by comparing the radical generation in linear and star-shaped TASN-centered crystalline polymers during their tensile deformation, we found that the TASN dissociation ratio is higher in the star-shaped polymer, which has more chains connected to the lamellar crystal. Thus, the microforces generated in the amorphous region during uniaxial stretching were probed via the use of TASN, which allowed a direct visualization of the necking initiation and propagation processes as well as a quantification via electron paramagnetic resonance spectroscopy.

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.

Development of Reactive Oxygen Species-Triggered Degradable Nanoparticles Using Oligoproline-Containing Peptides.

Oligoproline-containing peptides, GPPG and GPPPG, were designed and developed for nanoparticle-based delivery platforms, and their degradation is triggered by reactive oxygen species (ROS). Peptides containing more than two consecutive proline residues were found to be cleavable in 1 mM of ROS generated by hydrogen peroxide in the presence of CuSO4, which corresponds to plant cells under photosynthetic conditions. The nanoparticles formed by the peptides were also ROS-degradable and efficiently encapsulated a hydrophobic dye. The hydrophobic cargo in the peptide nanoparticles was released into the cytosol of plant leaf cells in response to the ROS generated in chloroplasts by light irradiation. Furthermore, local laser irradiation enabled the peptide nanoparticles to release their cargo at only the irradiated cell, promising site-selective cargo release triggered by irradiation.

Dual Peptide-Based Gene Delivery System for the Efficient Transfection of Plant Callus Cells.

Owing to their diverse functions and tunable physicochemical properties, peptides are promising alternatives to the conventional gene delivery tools that are available for plant systems. However, peptide-mediated gene delivery is limited by low transfection efficiency in plants because of the insufficient cytosolic translocation of DNA cargo. Here, we report a dual peptide-based gene delivery system for the efficient transfection of plant callus cells. This system is based on the combination of an artificial peptide composed of cationic cell-penetrating and hydrophobic endosomal escape domains with a gene carrier peptide composed of amphiphilic cell-penetrating and cationic DNA-binding domains. Cellular internalization and transfection studies revealed that this dual peptide-based system enables more efficient transfection of callus cells than does a carrier peptide alone by enhancing the endocytic uptake and subsequent cytosolic translocation of a carrier peptide/DNA complex. The present strategy will expand the utility of peptide-mediated plant gene delivery for a wide range of applications and basic research.

Zwitterionic Polypeptides: Chemoenzymatic Synthesis and Loosening Function for Cellulose Crystals.

A polypeptide with a GlyHisGly repeating sequence containing zwitterionic structures that effectively interact with cellulose was synthesized for dissociation of cellulose crystals. Polypeptide with the GlyHisGly sequence was synthesized by chemoenzymatic polymerization and postfunctionalization of the His residues was performed to afford imidazolium butyrate on the side chains. The resulting zwitterionic polypeptide effectively dissociated bundles of tunicate cellulose nanocrystals, even when the conditions were mild and the concentration of the polypeptide was as low as 1-2 mg mL-1. Polypeptide treatment also affected the morphology of the cell walls in cultured plant cells, and the cellulose microfibril networks and amorphous polysaccharide layer were dissociated according to atomic force microscopy (AFM). The zwitterionic polypeptide treatment did not change the crystal structure of the cellulose nanocrystals. Analysis of the mechanical properties of the cellulose nanocrystals by force curve measurements using AFM revealed that the elastic modulus of the cellulose nanocrystals increased after treatment with the zwitterionic polypeptide, indicating that the amorphous part of the cellulose nanocrystals was removed by interactions with the polypeptide. At a concentration of the polypeptide that enabled the dissociation of the cellulose network, the zwitterionic polypeptide showed negligible cytotoxicity to the plant cells. The mild and noncytotoxic technique for loosening cellulose microfibrils/nanocrystals that was developed in this study has tremendous significance for the modification of cellulose in terms of polymer chemistry, material science, and plant biotechnology.

Computational study on the polymerization reaction of d-aminopeptidase for the synthesis of d-peptides.

Almost all natural proteins are composed exclusively of l-amino acids, and this chirality influences their properties, functions, and selectivity. Proteases can recognize proteins composed of l-amino acids but display lower selectivity for their stereoisomers, d-amino acids. Taking this as an advantage, d-amino acids can be used to develop polypeptides or biobased materials with higher biostability. Chemoenzymatic peptide synthesis is a technique that uses proteases as biocatalysts to synthesize polypeptides, and d-stereospecific proteases can be used to synthesize polypeptides incorporating d-amino acids. However, engineered proteases with modified catalytic activities are required to allow the incorporation of d-amino acids with increased efficiency. To understand the stereospecificity presented by proteases and their involvement in polymerization reactions, we studied d-aminopeptidase. This enzyme displays the ability to efficiently synthesize poly d-alanine-based peptides under mild conditions. To elucidate the mechanisms involved in the unique specificity of d-aminopeptidase, we performed quantum mechanics/molecular mechanics simulations of its polymerization reaction and determined the energy barriers presented by the chiral substrates. The enzyme faces higher activation barriers for the acylation and aminolysis reactions with the l-stereoisomer than with the d-substrate (10.7 and 17.7 kcal mol-1 higher, respectively). The simulation results suggest that changes in the interaction of the substrate with Asn155 influence the stereospecificity of the polymerization reaction.