Simple Regulation of the Self-Assembling Ability by Multimerization of Elastin-Derived Peptide (FPGVG) n Using Nitrilotriacetic Acid as a Building Block

Exploring LCST- and UCST-like Behavior of Branched Molecules Bearing Repeat Units of Elastin-like Peptides as Side Components

Elastin-like peptides (ELPs) exhibit lower critical solution temperature (LCST)-type behavior, being soluble at low temperatures and insoluble at high temperatures. While the properties of linear, long-chain ELPs are well-studied, short-chain ELPs, especially those with branched architectures, have been less explored. Herein, to obtain further insights into multimeric short ELPs, we investigated the temperature-responsive properties of branched molecules composed of a repeating pentapeptide unit of short ELPs, Phe-Pro-Gly-Val-Gly, as side components and oligo(Glu) as a backbone structure. In turbidimetry experiments, the branched ELPs showed LCST-like behavior similar to conventional ELPs and upper critical solution temperature (UCST)-like behavior, which are rarely observed in ELPs. In addition, the morphological aspects and mechanisms underlying the temperature-responsiveness were investigated. We observed that spherical aggregates formed, and the branched ELPs underwent structural changes through the self-assembly process. This study demonstrates the unique temperature-responsiveness of branched short ELPs, providing new insights into the future development and use of ELPs with tailored properties.

Development of the efficient preparation method for thermoresponsive elastin-like peptides using liquid-phase synthesis combined with fragment condensation strategy

Elastin-like peptides (ELPs) are synthetic peptides that mimic the characteristic hydrophobic amino acid repeat sequences of elastin and exhibit temperature-dependent reversible self-assembly properties. ELPs are expected to be used as temperature-responsive biomolecular materials across diverse industrial and research fields, and there is a requirement for a straightforward method to mass-produce them. Previously, we demonstrated that phenylalanine-containing ELP analogs, namely, (FPGVG)n , can undergo coacervation with short chains (n = 5). The Fmoc solid-phase peptide synthesis method is one strategy used to synthesize these short ELPs. However, owing to its low reaction efficiency, an efficient method for preparing ELPs is required. In this study, efficient preparation of ELPs was investigated using a liquid-phase synthesis method with a hydrophobic benzyl alcohol support (HBA-tag). Because HBA-tags are highly hydrophobic, they can be easily precipitated by the addition of poor solvents and recovered by filtration. This property allows the method to combine the advantages of the simplicity of solid-phase methods and the high reaction efficiency of liquid-phase methods. By utilizing liquid-phase fragment condensation with HBA-tags, short ELPs were successfully obtained in high yield and purity. Finally, the temperature-dependent response of the ELPs generated through fragment condensation was assessed using turbidity measurements, which revealed a reversible phase transition. Consequently, the ELPs exhibited a reversible phase transition, indicating successful synthesis of ELPs via fragment preparation with tags. These findings provide evidence of the potential for mass production of ELPs using this approach.

Enhancement of Aggregate Formation Through Aromatic Compound Adsorption in Elastin-like Peptide (FPGVG)5 Analogs

Elastin-like peptides (ELPs) exhibit temperature-dependent reversible self-assembly. Repetitive sequences derived from elastin, such as Val-Pro-Gly-Val-Gly (VPGVG), are essential for the self-assembly of ELPs. Previously, we developed (FPGVG)5 (F5), in which the first valine residue in the VPGVG sequence was replaced with phenylalanine, which showed strong self-aggregation ability. This suggests that interactions through the aromatic amino acid residues of ELPs could play an important role in self-assembly. In this study, we investigated the thermoresponsive behavior of F5 analogs in the presence of aromatic compounds. Turbidimetry, spectroscopy, and fluorescence measurements demonstrated that aromatic compounds interacted with F5 analogs below the transition temperature and enhanced the self-assembly ability of ELPs by stabilizing amyloid-like structures. Furthermore, quantitative high-performance liquid chromatography analyses showed that the F5 analogs could adsorb and remove hydrophobic aromatic compounds from aqueous solutions during aggregate formation. These results suggested that the F5 analogs can be applicable as scavengers of aromatic compounds.

Branched short elastin-like peptides with temperature responsiveness obtained by EDTA-mediated multimerization

Elastin-like peptides (ELPs) exhibit a reversible phase transition, known as coacervation, triggered by temperature changes. This property makes them useful as stimuli-responsive molecular materials for various applications. Among ELPs, short peptide chain lengths have some advantages over long peptide chain lengths because short ELPs can be easily obtained by chemical synthesis, allowing the use of various amino acids, including D-type and unnatural amino acids, at any position in the sequence. Moreover, the incorporated amino acids readily affect the temperature-responsive behavior of ELPs. However, to be utilized in various applications, it is necessary to develop short ELPs and to investigate their temperature-responsive properties. To obtain further insights into the temperature-responsive behavior of the short ELPs, we investigated branched short ELP analogs composed of (FPGVG)_n chains (n = 1 or 2, abbreviated as F1 and F2, respectively). We synthesized multimers composed of four F1 chains or two to four F2 chains using ethylenediaminetetraacetic acid (EDTA) as a central component of multimerization. Our results show that the multimers obtained exhibited coacervation in aqueous solutions whereas linear F1 or F2 did not. Furthermore, the structural features of the obtained multimers were the same as those of linear (FPGVG)₄ . In this study, we demonstrated that molecules capable of coacervation can be obtained by multimerization of F1 or F2. The temperature-responsive molecules obtained using short ELPs make it possible to use them as easy-to-synthesize peptide tags to confer temperature responsiveness to various molecules, which will aid the development of temperature-responsive biomaterials with a wide variety of functions.

Peptide-based coacervates in therapeutic applications

Coacervates are droplets formed by liquid‒liquid phase separation. An increasing number of studies have reported that coacervates play an important role in living cells, such as in the generation of membraneless organelles, and peptides contribute to condensate droplet formation. Peptides with versatile functional groups and special secondary structures, including α-helices, β-sheets and intrinsically disordered regions, provide novel insights into coacervation, such as biomimetic protocells, neurodegenerative diseases, modulations of signal transmission, and drug delivery systems. In this review, we introduce different types of peptide-based coacervates and the principles of their interactions. Additionally, we summarize the thermodynamic and kinetic mechanisms of peptide-based coacervates and the associated factors, including salt, pH, and temperature, affecting the phase separation process. We illustrate recent studies on modulating the functions of peptide-based coacervates applied in biological diseases. Finally, we propose their promising broad applications and describe the challenges of peptide-based coacervates in the future.

Development of truncated elastin-like peptide analogues with improved temperature-response and self-assembling properties

Functional peptides, which are composed of proteinogenic natural amino acids, are expected to be used as biomaterials with minimal environmental impact. Synthesizing a functional peptide with a shorter amino acid sequence while retaining its function is a easy and economical strategy. Furthermore, shortening functional peptides helps to elucidate the mechanism of their functional core region. Truncated elastin-like peptides (ELPs) are peptides consisting of repetitive sequences, derived from the elastic protein tropoelastin, that show the thermosensitive formation of coacervates. In this study, to obtain shortened ELP analogues, we synthesized several (Phe-Pro-Gly-Val-Gly)_n (FPGVG)_n analogues with one or two amino acid residues deleted from each repeat sequence, such as the peptide analogues consisting of FPGV and/or FPG sequences. Among the novel truncated ELP analogues, the 16-mer (FPGV)₄ exhibited a stronger coacervation ability than the 25-mer (FPGVG)₅. These results indicated that the coacervation ability of truncated ELPs was affected by the amino acid sequence and not by the peptide chain length. Based on this finding, we prepared Cd²⁺-binding sequence-conjugated ELP analogue, AADAAC-(FPGV)₄, and found that it could capture Cd²⁺. These results indicated that the 16-mer (FPGV)₄ only composed of proteinogenic amino acids could be a new biomaterial with low environmental impact.

Flexible customization of the self-assembling abilities of short elastin-like peptide Fn analogs by substituting N-terminal amino acids

Elastin-like peptides (ELPs) are thermoresponsive biopolymers inspired by the characteristic repetitive sequences of natural elastin. As ELPs exhibit temperature-dependent reversible self-assembly, they are expected to be biocompatible thermoresponsive materials for drug delivery carriers. One of the most widely studied ELPs in this field is the repetitive pentapeptide, (VPGXG)_n . We previously reported that phenylalanine-containing ELP (Fn) analogs, in which the former Val residue of the repetitive sequence (VPGVG)_n is replaced by Phe, show coacervation with a short chain length (n = 5). Owing to their short sequences, Fn analogs are easily modified in amino acid sequences via simple chemical synthesis, and are useful for investigating the relationship between peptide sequences and temperature responsiveness. In this study, we developed Fn analogs by replacing Phe residue(s) with other amino acids or introducing another amino acid at the N-terminus. The temperature responsiveness of the Fn analogs changed drastically with the substitution of a single Phe residue, suggesting that aromatic amino acids play an important role in their self-assembly. In addition, the self-assembling ability of Fn was enhanced by increasing the bulkiness of the N-terminal amino acids. Therefore, the N-terminal residue was considered to be important for hydrophobicity-induced intermolecular interactions between the peptides during coacervation.

Metal ion scavenging activity of elastin-like peptide analogues containing a cadmium ion binding sequence

The development of simple and safe methods for recovering environmental pollutants, such as heavy metals, is needed for sustainable environmental management. Short elastin-like peptide (ELP) analogues conjugated with metal chelating agents are considered to be useful as metal sequestering agents as they are readily produced, environment friendly, and the metal binding domain can be selected based on any target metal of interest. Due to the temperature dependent self-assembly of ELP, the peptide-based sequestering agents can be transformed from the solution state into the particles that chelate metal ions, which can then be collected as precipitates. In this study, we developed a peptide-based sequestering agent, AADAAC-(FPGVG)₄, by introducing the metal-binding sequence AADAAC on the N-terminus of a short ELP, (FPGVG)₄. In turbidity measurements, AADAAC-(FPGVG)₄ revealed strong self-assembling ability in the presence of metal ions such as Cd²⁺ and Zn²⁺. The results from colorimetric analysis indicated that AADAAC-(FPGVG)₄ could capture Cd²⁺ and Zn²⁺. Furthermore, AADAAC-(FPGVG)₄ that bound to metal ions could be readily recycled by treatment with acidic solution without compromising its metal binding affinity. The present study indicates that the fusion of the metal-binding sequence and ELP is a useful and powerful strategy to develop cost-effective heavy metal scavenging agents with low environmental impacts.