Gold nanoparticles-anchored peptides enable precise colorimetric estimation of microplastics

Microplastics (MPs, particle size < 5 mm) are an emerging contaminant in aquatic environment, which have attracted increasing attention worldwide. In this study, a colorimetric method for MPs detection was developed based on gold nanoparticles (AuNPs)-anchored peptides (LCI or TA2), which are able to specifically recognize and adhere to polypropylene (PP) or polystyrene (PS). The AuNPs-anchored peptides accumulated on the surface of MPs, rendering a color change from red to gray-blue and transforming the surface plasmon absorption intensity and wavelength. The designed method presented high selectivity, stability, and reproducibility, with a detection range of 2.5-15 μg/mL. The results demonstrated that the developed approach will be valuable in the precise, facile, and cost-effective estimation of MPs in different matrices, regulating the control over MPs pollution and its hazardous impact on health and ecosystems.

Identification of Water-Soluble Polymers through Discrimination of Multiple Optical Signals from a Single Peptide Sensor

The pollution of water environments is a worldwide concern. Not only marine pollution by plastic litter, including microplastics, but also the spillage of water-soluble synthetic polymers in wastewater have recently gained increasing attention due to their potential risks to soil and water environments. However, conventional methods to identify polymers dissolved in water are laborious and time-consuming. Here, we propose a simple approach to identify synthetic polymers dissolved in water using a peptide-based molecular sensor with a fluorophore unit. Supervised machine learning of multiple fluorescence signals from the sensor, which specifically or nonspecifically interacted with the polymers, was applied for polymer classification as a proof of principle demonstration. Aqueous solutions containing different polymers or multiple polymer species with different mixture ratios were identified successfully. We found that fluorophore-introduced biomolecular sensors have great potential to provide discriminative information regarding water-soluble polymers. Our approach based on the discrimination of multiple optical signals of water-soluble polymers from peptide-based molecular sensors through machine learning will be applicable to next-generation sensing systems for polymers in wastewater or natural environments.

Design of peptides with strong binding affinity to poly(methyl methacrylate) resin by use of molecular simulation-based materials informatics

Peptides with strong binding affinities for poly(methyl methacrylate) (PMMA) resin were designed by use of materials informatics technology based on molecular dynamics simulation for the purpose of covering the resin surface with adhesive peptides, which were expected to result in eco-friendly and biocompatible biomaterials. From the results of binding affinity obtained with this molecular simulation, it was confirmed that experimental values could be predicted with errors <10%. By analyzing the simulation data with the response-surface method, we found that three peptides (RWWRPWW, EWWRPWR, and RWWRPWR), which consist of arginine (R), tryptophan (W), and proline (P), have strong binding affinity to the PMMA resin. These amino acids were effective because arginine and tryptophan have strong binding affinities for methoxycarbonyl groups and methyl groups, which are the main constituents of the PMMA resin, and proline stabilizes the flat zigzag structures of the peptides in water. The strong binding affinities of the three peptides were confirmed by experiments (surface plasmon resonance methods).

Preparation of Polymer-Immobilized Polyimide Films Using Hot Pressing and Titania Coatings

Recent studies have revealed that polymer molecules at film surfaces exhibit unique physical properties compared to those in bulk. On the other hand, such a topic has not been extensively focused for the cases of rigid polymers such as polyimide (PI). This study investigated whether hot pressing could induce the immobilization of other polymers, poly(4-vinylphenol) (PVP), on PI film surfaces. Results supported the immobilization of PVP on the PI film surfaces, and the increase of hot-press temperature resulted in the increase of the immobilization amount of PVP. The mechanism of immobilization is discussed considering the effects of hot pressing on the interactions between PVP and PI at the interfaces of their films. Sol-gel titania coatings were further conducted to the obtained PVP-immobilized PI films. The effect of PVP immobilization on formability and the adhesion of titania layers on the film surfaces were evaluated. These results demonstrate that hot pressing of other polymers is a useful approach for the surface modification of PI films, particularly introducing certain functional groups, and indicate that the polymer immobilization mechanism might be correlated with the surface physical properties of PI films.

Anchor peptides promote degradation of mixed plastics for recycling

Resource stewardship and sustainable use of natural resources is mandatory for a circular plastic economy. The discovery of microbes and enzymes that can selectively degrade mixed-plastic waste enables to recycle plastics. Knowledge on how to achieve efficient and selective enzymatic plastic degradation is a key prerequisite for biocatalytic recycling of plastics. Wild-type natural polymer degrading enzymes such as cellulases pose often selective non-catalytic binding domains that facilitate a targeting and efficient degradation of polymeric substrates. Recently identified polyester hydrolases with synthetic polymer degrading activities, however, lack in general such selective domains. Inspired by nature, we herein report a protocol for the identification and engineering of anchor peptides which serve as non-catalytic binding domains specifically toward synthetic plastics. The identified anchor peptides hold the promise to be fused to known plastic degrading enzymes and thereby enhance the efficiency of biocatalytic plastic recycling processes.

Affinity-based thermoresponsive fluorescence switching of proteins conjugated with a polymer-binding peptide

The affinity-based thermoresponsive fluorescence switching of proteins conjugated with a polymer-binding peptide is demonstrated. The specific affinity of the peptide and thermoresponsive structural transitions of the polymer are essential for reliable fluorescence switching behavior.

Preparation of Biocomposite Soft Nanoparticles Composed of Poly(Propylene Oxide) and the Polymer-Binding Peptides

The molecular recognition capability of naturally occurring biomolecules is generally expressed against biomolecules in the biological milieu. Recently, it was demonstrated that the specific interactions of biomolecules such as short peptides were applicable to artificial materials. We have developed peptides with specific affinities for synthetic polymers toward functional biocomposite polymeric materials. In this study, we demonstrated the preparation of biocomposite nanoparticles composed of poly(propylene oxide) (PPO) and PPO-binding peptides. A simple injection of a concentrated PPO solution dissolved in an organic solvent into the peptide solution under sonication resulted in the formation of nanospherical structures. Morphological observation indicated characteristic softness and high applicability as a molecular carrier of the biocomposite nanoparticles. Structural characterization of PPO and the PPO-binding peptide revealed the structural conformability of these molecules to interact specifically with each other. Our findings expand the potential applicability of polymer-binding peptides for the future construction of biomedical materials composed of peptides and various polymers.

Affinity-Based Functionalization of Biomedically Utilized Micelles Composed of Triblock Copolymers through Polymer-Binding Peptides

Polymeric micelles and vesicles that are self-assembled from amphiphilic block copolymers are frequently used in biomedical applications. Poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-PEO, so-called Pluronic, is a Food and Drug Administration approved triblock copolymer utilized in biomedical applications. However, the control of drug loading and surface functionalization of micelles remain challenging due to structural limitations. In this study, Pluronic micelles with various structures were rationally functionalized via the PPO-binding peptide, which was previously identified using a biologically constructed peptide library displayed on filamentous phages. The interactions between the peptide and Pluronic micelles were characterized in detail based on fluorescence changes in an extrinsic fluorescence dye, and a sufficient PPO chain length of Pluronic was essential for the interactions. Furthermore, enzymatic degradation of the model substrate-conjugated peptide loaded into Pluronic micelles showed stable loading of the peptide. Importantly, the exposure level of the conjugated molecules to the peptide was dependent on the PEO chain length of Pluronic, suggesting controllable functionalization of polymeric micelles. Anticancer drug-conjugated peptide-loaded Pluronic micelles with suitable polymeric structures were applied in a cell culture assay. The anticancer efficacy of the loaded drugs can be controlled by the molecular design of the binding peptide and polymers. These results demonstrate that an affinity-based functionalization strategy may facilitate polymeric micelles for various biomedical applications.

KnowVolution of the Polymer-Binding Peptide LCI for Improved Polypropylene Binding

The functionalization of polymer surfaces by polymer-binding peptides offers tremendous opportunities for directed immobilization of enzymes, bioactive peptides, and antigens. The application of polymer-binding peptides as adhesion promoters requires reliable and stable binding under process conditions. Molecular modes of interactions between material surfaces, peptides, and solvent are often not understood to an extent that enables (semi-) rational design of polymer-binding peptides, hindering the full exploitation of their potential. Knowledge-gaining directed evolution (KnowVolution) is an efficient protein engineering strategy that facilitates tailoring protein properties to application demands through a combination of directed evolution and computational guided protein design. A single round of KnowVolution was performed to gain molecular insights into liquid chromatography peak I peptide, 47 aa (LCI)-binding to polypropylene (PP) in the presence of the competing surfactant Triton X-100. KnowVolution yielded a total of 8 key positions (D19, S27, Y29, D31, G35, I40, E42, and D45), which govern PP-binding in the presence of Triton X-100. The recombination of two of the identified amino acid substitutions (Y29R and G35R; variant KR-2) yielded a 5.4 ± 0.5-fold stronger PP-binding peptide compared to LCI WT in the presence of Triton X-100 (1 mM). The LCI variant KR-2 shows a maximum binding capacity of 8.8 ± 0.1 pmol/cm² on PP in the presence of Triton X-100 (up to 1 mM). The KnowVolution approach enables the development of polymer-binding peptides, which efficiently coat and functionalize PP surfaces and withstand surfactant concentrations that are commonly used, such as in household detergents.

Filamentous Virus-based Assembly: Their Oriented Structures and Thermal Diffusivity

Organic polymers are generally regarded as thermal insulators because amorphous arrangement of molecular chains reduces the mean free path of heat-conducting phonons. However, recent studies indicated that single chains of polymers with highly oriented structures could have high thermal conductivity than bulk polymers because stretched polymer chains effectively conduct phonons through polymeric covalent bonds. Here, we demonstrated the possibility of non-covalent virus assembly prepared by simple flow-induced methods toward high thermal conductive polymeric materials. Films with high thermal diffusivity composed of non-covalent bond-based assemblies of liquid crystalline filamentous viruses were prepared using a simple flow-induced orientation method. Structural and thermal characterization demonstrated that highly oriented structures of the viruses in the film were attributed to the high thermal diffusivity. Our results will open attractive opportunities for biomolecular-based thermally conductive soft materials even though the assemblies are based on non-covalent bonds.

Bioinspired structural transition of synthetic polymers through biomolecular ligand binding

The bioinspired structural transition of thermoresponsive poly(N-isopropylacrylamide) was demonstrated by specific ligand binding of artificially evolved peptides to the polymer.

Surface functionalization of polymer substrates with hydroxyapatite using polymer-binding peptides

Material-binding peptides are used as non-covalent bond linkers for surface functionalization because they bind to materials under mild conditions without affecting the properties of the materials and are functionalized by conjugating with other molecules. In the present study, the surface functionalization of polyetherimide (PEI) with hydroxyapatite (HAp) was examined using two types of PEI-binding peptides conjugated with other sequences. One peptide consisted of PEI-binding peptide p1 (TGADLNT) and a triasparate sequence for the biomimetic mineralization of HAp in simulated body fluids (SBFs), while the other consisted of p1 and HAp-binding peptide (HABP, CMLPHHGAC) for the immobilization of HAp and amorphous calcium phosphate (ACP) nanoparticles. The results obtained revealed deposits of HAp on PEI films treated with the peptide consisting of p1 and triasparate. HAp and ACP nanoparticles were immobilized on PEI films treated with peptides consisting of p1 and HABP, and immersion of the resultant substrates in SBFs completely covered the surfaces of PEI films with HAp.

Affinity-based release of polymer-binding peptides from hydrogels with the target segments of peptides

Peptides with affinities for the target segments of polymer hydrogels were identified by phage display methods and exhibited affinity-based release capability from the hydrogels. The sustained anticancer effects of the drug-conjugated peptides were also demonstrated by their release from the hydrogels.

Affinity-based thermoresponsive precipitation of proteins modified with polymer-binding peptides

A model protein (i.e., human serum albumin) chemically modified with a 12-mer peptide with an affinity for the meso diad sequence of poly(N-isopropylacrylamide) (PNIPAM) was successfully precipitated with PNIPAM above the lower critical solution temperature of PNIPAM.

Identification of Soft Matter Binding Peptide Ligands Using Phage Display

Phage display is a powerful tool for the selection of highly affine, short peptide ligands. While originally primarily used for the identification of ligands to proteins, the scope of this technique has significantly expanded over the past two decades. Phage display nowadays is also increasingly applied to identify ligands that selectively bind with high affinity to a broad range of other substrates including natural and biological polymers as well as a variety of low-molecular-weight organic molecules. Such peptides are of interest for various reasons. The ability to selectively and with high affinity bind to the substrate of interest allows the conjugation or immobilization of, e.g., nanoparticles or biomolecules, or generally, facilitates interactions at materials interfaces. On the other hand, presentation of peptide ligands that selectively bind to low-molecular-weight organic materials is of interest for the development of sensor surfaces. The aim of this article is to highlight the opportunities provided by phage display for the identification of peptide ligands that bind to synthetic or natural polymer substrates or to small organic molecules. The article will first provide an overview of the different peptide ligands that have been identified by phage display that bind to these "soft matter" targets. The second part of the article will discuss the different characterization techniques that allow the determination of the affinity of the identified ligands to the respective substrates.

Screening of peptides recognizing simple polycyclic aromatic hydrocarbons

Peptides that specifically bind to the simplest polycyclic aromatic hydrocarbon, naphthalene, were obtained by affinity-based screening using a phage-displayed peptide library. The identified peptide with a β-turn structure showed specific binding to naphthalene present not only on substrates but also in aqueous solutions.

Peptide-mediated nanoengineering of inorganic particle surfaces: a general route toward surface functionalization via peptide adhesion domains

The peptide-mediated functionalization of inorganic particle surfaces is demonstrated on gadolinium oxide (GdO) particles, revealing specific means to functionalize nano- or microparticles. Phage display screening is exploited to select 12mer peptides, which exhibit sequence-specific adhesion onto surfaces of GdO particles. These peptide adhesion domains are exploited to effectively decorate GdO particles with fluorescently labeled poly(ethylene oxide) (PEO), proving to result in a stable surface modification as shown by significant reduction of protein adsorption by 80%, compared to nonfunctionalized particles. Peptide adhesion and stability of the noncovalent coating are investigated by adsorption/elution experiments and Langmuir isotherms. Fluorescence microscopy, contact angle, and energy dispersive X-ray (EDX) measurements confirmed the sequence specificity of the interactions by comparing adhesion sequences with scrambled peptide sequences. Noncovalent, but specific modification of inorganic particle surfaces represents a generic strategy to modulate functionality and function of nano- or microparticle surfaces.