Affinity-Based Screening of Peptides Recognizing Assembly States of Self-Assembling Peptide Nanomaterials

Mariz B, Moreira IP, Kalafatovic D, Morais Faustino BM, Narang V, Wang T, Pappas CG, Ferreira I, Roque ACA, Ulijn RV. Discovery of phosphotyrosine-binding oligopeptides with supramolecular target selectivity

Phage-display screening on self-assembled tyrosine-phosphate ligands enables the identification of oligopeptides selective to dynamic supramolecular targets, with the lead peptide showing a preferred hairpin-like conformation and catalytic activity.

A Versatile Method for the End-Functionalization of Polycarbenes

End-functionalization is an effective strategy for constructing functional materials. A method for chain-end functionalization of helical polycarbenes is herein developed that relied on Sonogashira coupling reaction. In this work, a family of helical polycarbenes with controlled molecular mass (M_n ) and low polydispersity (M_w /M_n ) is readily prepared using Pd(II) and the Wei-Phos ligand as initiator. The Pd(II) complex is confirmed to remain at the chain end of polycarbene. Subsequently, a series of terminal alkyne derivatives with interesting functional groups, including the F atom, aldehyde, or anthracene groups, are synthesized. They could be installed at the chain end of polycarbene through Sonogashira coupling reaction catalyzed by the Pd(II) complex at the chain end. Moreover, a couple of hybrid block copolymers are easily obtained by installing terminal alkynes modified by another type of polymer. The structures of the isolated polymers are confirmed by ¹ H nuclear magnetic resonance (¹ H NMR), ¹⁹ F nuclear magnetic resonance (¹⁹ F NMR), ³¹ P nuclear magnetic resonance (³¹ P NMR), and Fourier transform infrared spectroscopy (FT-IR), respectively. The self-assembly properties of the hybrid block copolymers are also investigated by atomic force spectroscopy analysis. By the hereby developed method, various functional groups can be introduced at the chain end of helical polycarbenes for constructing functional polymer materials, moreover, the transition metal residues at the end of polymer chains can be easily removed.

Discovery of Surfactant-Like Peptides from a Phage-Displayed Peptide Library

Peptides with specific affinities for various materials have been identified in the past three decades and utilized in materials science and engineering. A peptide's capability to specifically interact with materials is not naturally derived but screened from a biologically constructed peptide library displayed on phages or cells. To date, due to limitations in the screening procedure, the function of screened peptides has been primarily limited to the affinity for target materials. Herein, we demonstrated the screening of surfactant-like peptides from a phage-displayed peptide library. A screened phage clone displaying a peptide showed high activity for accumulating at emulsion surfaces with certain assembled structures, resulting in stable emulsions. The surface tension for the solution of the chemically synthesized peptide decreased with increasing peptide concentration, demonstrating certain surface activity, which corresponded to the ability to decrease the surface tension of liquids (e.g., water), owing to the accumulation of molecules at the air-liquid or liquid-liquid interface. Peptides with a randomized sequence did not lower the surface tension, indicating the essential role of amino acid sequences in surface activity. Our strategy for identifying novel functional peptides from a phage-displayed peptide library can be used to expand the applicability of peptidyl materials and biosurfactants.

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.

Designer aromatic peptide amphiphiles for self-assembly and enzymatic display of proteins with morphology control

We herein designed bi-functional aromatic peptide amphiphiles both self-assembling to fibrous nanomaterials and working as a substrate of microbial transglutaminase, leading to peptidyl scaffolds with different morphologies that can be enzymatically post-functionalized with proteins.

Self-assembling peptide nanofibers promoting cell adhesion and differentiation

There is an increasing need for the development of functional artificial extracellular matrices (ECMs) for tissue engineering. Recently, we have successfully designed a self-assembling peptide, named E1Y9, to construct functional ECMs. We describe here an enhancement of abilities of E1Y9 materials to promote cell adhesion and differentiation, using functional peptide sequences derived from natural extracellular matrix proteins. We designed functionalized self-assembling peptides, RGDS-conjugated E1Y9 (E1Y9-RGDS) and IKVAV-conjugated E1Y9 (E1Y9-IKVAV). E1Y9-RGDS and E1Y9-IKVAV formed peptide nanofibers in a similar manner to E1Y9, with β-sheet secondary structures. Surfaces coated with peptide nanofibers displayed the higher bioactivities of E1Y9-RGDS for cell adhesion and E1Y9-IKVAV for cell differentiation than those of E1Y9, with the activities being dependent on the concentrations of the functional peptides. These functionalized peptides will be useful for the construction of functional ECMs in cell and tissue engineering.

Screening of Oligopeptides that Recognize Inorganic Crystalline Facets of Metal Nanoparticles

Peptides that possess specific affinity to distinct crystal facets have been reported previously. However, their adsorption behavior in terms of the crystal sizes and shapes is less exploited. Herein, we isolate several phage clones that show the strong affinity to {100} of Pd at a neutral pH from the M13 phage library, and among them the phages that have shape selectivity to the cubic structure are identified by eliminating ones that bind randomly shaped Pd nanoparticles (NPs). Since Pd nanocube-binding phages are eluted by lowering pH values in the biopanning process, the selected phages (and their binding peptides displayed on protein pIII) can be released from Pd surfaces through pH changes. We used this feature to modulate the capping density of selected peptides on NPs. For example, when less peptides are capped on Pd nanocubes by lowering the pH values, the shape of the nanocubes is deformed and some evolve into a concave shape, indicating that Pd atoms are released from the less protected {100} facet selectively due to the higher surface energy. This type of crystalline facet-recognizing peptides can be applied for smart capping agents that not only bind target crystalline planes, but also modify their coverage on the specific surfaces with pH changes. The peptide-capping agents could be useful to fabricate NPs with characteristic shapes through etching and adsorption of atoms on specific crystalline planes of seed nanocrystals.

Fabrication of gold nanoparticles on biotin-di-tryptophan scaffold for plausible biomedical applications

AuNPs were synthesized and encapsulated by spherical scaffold of biotinylated di-tryptophan and such devices can be used for plausible biomedical applications.

Peptide-induced affinity binding of carbonic anhydrase to carbon nanotubes

Although affinity binding between short chain peptides and carbon nanotube (CNT) has been reported, little is known for the study of proteins with CNT recognition and specific binding capabilities. Herein, carbonic anhydrase (CA) was functionalized via protein fusion with a single-walled carbon nanotube (SWNTs)-binding peptide, thereby forming a bioactive protein with high affinity binding capability. TEM and AFM analyses showed that the fusion CA could firmly coat to SWNTs with a surface coverage over 51%, while the enzyme maintained its catalytic activity. Structural analysis revealed that slight conformation changes were induced as a result of the fusion; however, the affinity binding of CA to the hydrophobic surface of SWNTs restored the native structure of the protein, with the conformation of the SWNT-bound CA largely resembling that of the native parent enzyme. Interfacial interactions between the fusion CA and SWNT were further investigated with Raman spectrometry and microscopic analysis. The results suggested that such peptide-induced CNT-protein binding allows the development of bioactive hybrid materials with the native structures of the protein moieties largely undisrupted.

A robust route to enzymatically functional, hierarchically self-assembled peptide frameworks

The addition of enzyme biofunctionality to self-assembling peptide nanofibers is challenging since such additions can inhibit functionality or self-assembly. We introduce a method for peptide nanofiber enzyme functionalization, demonstrated by the attachment of a polymerization synthase to peptide nanofibers. The enzyme generates a biocompatible, biodegradable biopolyester coat on the fibers with applicablity in medical engineering. This approach provides a template for generation of functional bionanomaterials.

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.

Polymer-binding peptides for the noncovalent modification of polymer surfaces: effects of peptide density on the subsequent immobilization of functional proteins

Peptides that specifically bind to polyetherimide (PEI) were selected, characterized, and used for the noncovalent modification of the PEI surface. The peptides were successfully identified from a phage-displayed peptide library. A chemically-synthesized peptide composed of the Thr-Gly-Ala-Asp-Leu-Asn-Thr sequence showed an extremely high binding constant for the PEI films (5.6 × 10(8) M(-1)), which was more than three orders of magnitude greater than that for the reference polystyrene films. The peptide was biotinylated and immobilized onto the PEI films to further immobilize streptavidin (SAv). The amount of SAv bound depended on the density of immobilized peptide. It gradually increased with an increasing density of immobilized peptide and achieved a maximum (2.1 pmol cm(-2)) at a peptide density of 19.8 pmol cm(-2). The ratio of peptide used for immobilizing SAv at the maximum value was only 11%, and was partially due to the low accessibility of SAv to the biotin moieties on the PEI films. Moreover, the amount of SAv bound gradually decreased at higher peptide densities, suggesting that the clustering of the peptides also inhibited the binding of SAv. Furthermore, peptides on the PEI films promoted the uniform immobilization of SAv with less structural denaturing. The immobilized SAv was able to further immobilize probe DNA to hybridize with its complementary DNA. These present results suggest that the density of immobilized peptide has a great impact on the surface modifications using polymer-binding peptides.