Structure and dynamics of self-assembling beta-sheet peptide tapes by dynamic light scattering

Effect of Peptide-Polymer Host-Guest Electrostatic Interactions on Self-Assembling Peptide Hydrogels Structural and Mechanical Properties and Polymer Diffusivity

Peptide-based supramolecular hydrogels are an attractive class of soft materials for biomedical applications when biocompatibility is a key requirement as they exploit the physical self-assembly of short self-assembling peptides avoiding the need for chemical cross-linking. Based on the knowledge developed through our previous work, we designed two novel peptides, E(FKFE)2 and K(FEFK)2, that form transparent hydrogels at pH 7. We characterized the phase behavior of these peptides and showed the clear link that exists between the charge carried by the peptides and the physical state of the samples. We subsequently demonstrate the cytocompatibility of the hydrogel and its suitability for 3D cell culture using 3T3 fibroblasts and human mesenchymal stem cells. We then loaded the hydrogels with two polymers, poly-l-lysine and dextran. When polymer and peptide fibers carry opposite charges, the size of the elemental fibril formed decreases, while the overall level of fiber aggregation and fiber bundle formation increases. This overall network topology change, and increase in cross-link stability and density, leads to an overall increase in the hydrogel mechanical properties and stability, i.e., resistance to swelling when placed in excess media. Finally, we investigate the diffusion of the polymers out of the hydrogels and show how electrostatic interactions can be used to control the release of large molecules. The work clearly shows how polymers can be used to tailor the properties of peptide hydrogels through guided intermolecular interactions and demonstrates the potential of these new soft hydrogels for use in the biomedical field in particular for delivery or large molecular payloads and cells as well as scaffolds for 3D cell culture.

Helical Superstructures from the Hierarchical Self-Assembly of Coil-Coil Block Copolymer Guided by Side Chain Amyloid-β(17-19) LVF Peptide

The rational design of precisely controlled hierarchical chiral nanostructures from synthetic polymers garnered inspiration from sophisticated biological materials. Since chiral peptide motifs induce helix formation in macromolecules, herein we report the synthesis of a novel type of hybrid polymer consisting of a β-sheet forming a LVF [L = leucine, V = valine, and F = phenylalanine] tripeptide pendant polymethacrylate block and a poly[poly(ethylene glycol) methyl ether methacrylate] (PPEGMA) block. The designed block copolymer self-organized into helical superstructures with a left-handed twisting sense, as visualized by field emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. This intriguing hierarchical self-assembly is driven by the minimalistic peptide motif that itself has a high propensity to adopt an antiparallel β-sheet conformation. We also report the generation of a diverse array of nanostructures, including spherical micelles, spindle micelles, rod-like micelles, vesicles, helical supramolecular fibers, and helical toroids via self-assembly of the designed block copolymer in tetrahydrofuran/water mixed solvents. To realize the observable helical superstructure, a twisted two-dimensional core-shell tape is proposed as a structure model in which the peptide segments form an antiparallel β-sheet with a polymer shell. The findings contribute to the advancement of a helical polymer or the superhelical self-assembly of polymers, paving the way for diverse applications in materials science and related fields.

Surface Accumulation of Cerium, Self-Assembling Peptide, and Fluoride on Sound Bovine Enamel

The accumulation of caries-preventive compounds on sound enamel is crucial in order to improve the inhibition of carious lesion initiation. The aim of this research was to investigate the initial accumulation of cerium, oligopeptide p11-4, and fluoride from NaF or amine fluoride (AmF) on sound enamel in vitro by means of energy dispersive X-ray spectroscopy (EDX). Polished bovine enamel specimens (n = 120 from 60 teeth) were fabricated. Out of these, 12 specimens each were treated with CeCl3 (cerium(III) chloride heptahydrate 25%), oligopeptide p11-4 (Curodont Repair, Credentis), NaF (10,000 ppm F−), AmF (amine fluoride, Elmex Fluid, CP-GABA GmbH, 10,000 ppm F−), or Aqua demin (control). After rinsing with water, the surface elemental composition (Ce, N, F, Ca, P, O, Na, Mg) was measured (EDX; EDAX Octane Elect detector, APEX v2.0), expressed in atomic percent (At%) and analyzed (non-parametric statistics, α = 0.05, error rates method). Another 12 specimens per treatment group were fabricated and used for analyzing accumulation in cross-sections with EDX linescans and two-dimensional EDX-mappings. The surface median atomic percent of cerium (At%Ce) was 0.8 for CeCl3, but no Ce was found for any other group. N, specifically for oligopeptide p11-4, could not be detected. Fluorine could only be detected on fluoridated surfaces. The median atomic percent of fluorine (At%F) was 15.2 for NaF and 17.0 for AmF. The Ca/P ratio increased significantly compared to the control following the application of NaF and AmF (p < 0.001), but decreased significantly for CeCl3 (p < 0.001). In cross-sectioned specimens of the CeCl3-group, 12.5% of the linescans revealed cerium at the enamel surface, whereas 83.3% of the NaF linescans and 95.8% of the AmF linescans revealed fluorine at the enamel surface. Following the application of oligopeptide p11-4, no traces of N were detectable. In the depth of the samples, no signal was detected for any of the corresponding elements exceeding the background noise. Cerium and fluorine (from both NaF and AmF), but not the oligopeptide p11-4, precipitated on sound enamel.

Investigating the effects of N-terminal acetylation on KFE8 self-assembly with 2D IR spectroscopy

Peptide self-assembly is an exciting and robust approach to create novel nanoscale materials for biomedical applications. However, the complex interplay between intra- and intermolecular interactions in peptide aggregation means that minor changes in peptide sequence can yield dramatic changes in supramolecular structure. Here, we use two-dimensional infrared (2D IR) spectroscopy to study a model amphiphilic peptide, KFE8, and its N-terminal acetylated counterpart, AcKFE8. 2D IR spectra of isotope-labeled peptides reveal that AcKFE8 aggregates comprise two distinct β-sheet structures while KFE8 aggregates comprise only one of these structures. Using an excitonic Hamiltonian to simulate the vibrational spectra of model β-sheets, we determine that the spectra are consistent with antiparallel β-sheets with different strand alignments, specifically a two-residue shift in the register of the β-strands. These findings bring forth new insights into how N-terminal acetylation may subtly impact secondary structure, leading to larger effects on overall aggregate morphology. Additionally, these results highlight the importance of understanding the residue-level structural differences that result from changes in peptide sequence in order to facilitate the rational design of peptide materials.

Remineralization potential of P11-4 and fluoride on secondary carious primary enamel: A quantitative evaluation using microcomputed tomography

The aim of this study was to assess the ability of self-assembling peptide (P11-4) diffusion, assembly, and remineralization to effect artificial secondary caries-like lesions in human primary teeth in vitro. Enamel-dentin blocks obtained from extracted human primary molars were embedded into epoxy resin blocks. Cavities (approximately 1 × 1 × 2 mm) were prepared on the surface using a high-speed diamond bur under constant water cooling and filled with composite restorative material (Filtek Z250; 3 M ESPE). The samples were immersed in demineralizing solution (20 ml) for 96 h to produce secondary caries lesions and divided into two groups according to the testing materials: fluoride varnish (Duraphat; Colgate, UK) and P11-4 (Curodont Repair; Credentis, Switzerland). Except for the control areas, all samples were remineralized for 3-5 min using the remineralizing agents, and then all the sections were placed in a pH-cycling system for 5 days at 35°C. The pH cycling procedure was followed by micro-CT analysis for the qualitative evaluation of surface changes. The Mann-Whitney U test was used to compare two independent groups. In the comparison of more than two dependent groups, Bonferroni smoothed pairwise analyses were used to determine the source of the Kruskal-Wallis H test difference. The results of the study revealed that the remineralization depths of the peptide group were higher than those of the fluoride group (p < .01). There was a statistically significant difference in remineralization effects between the fluoride and peptide groups. P11-4 can be considered as an effective remineralizing agent for secondary caries lesions.

Effect of the caries-protective self-assembling peptide P11-4 on shear bond strength of metal brackets

Purpose

During orthodontic treatment with fixed appliances, demineralization around brackets often occurs. The aim of this in vitro study was to investigate the effect of the caries-protective self-assembling peptide P11‑4 (SAP P11-4) on the shear bond strength of metal brackets.

Methods

In all, 45 extracted human wisdom teeth were available for the study. The teeth were randomly divided into 3 groups (each n = 15) and pretreated as follows: test group 1: application of SAP P11‑4 (Curodont Repair, Windisch, Switzerland) and storage for 24 h in artificial saliva; test group 2: application of SAP P11‑4; control group: no pretreatment with SAP P11‑4. A conventional metal maxillary incisor bracket (Discovery, Dentaurum, Ispringen) was adhesively bonded to each buccal surface. The shear bond strength was tested according to DIN 13990. After shearing, the Adhesive Remnant Index (ARI) was determined microscopically (10 × magnification). Analysis of variance (ANOVA) was used to check the groups for significant differences (α = 0.05). The distribution of the ARI scores was determined with the χ ² test.

Results

There was no significant difference in shear forces between the groups (p = 0.121): test group 1 = 17.0 ± 4.51 MPa, test group 2 = 14.01 ± 2.51 MPa, control group 15.54 ± 4.34 MPa. The distribution of the ARI scores between the groups did not vary (p-values = 0.052–0.819).

Conclusion

The application of the caries protective SAP P11‑4 before bonding of brackets did not affect the shear bond strength. Therefore, pretreatment of the enamel surface with SAP P11‑4 shortly before bracket insertion can be considered.

Protein folding and assembly in confined environments: Implications for protein aggregation in hydrogels and tissues

In the biological milieu of a cell, soluble crowding molecules and rigid confined environments strongly influence whether the protein is properly folded, intrinsically disordered proteins assemble into distinct phases, or a denatured or aggregated protein species is favored. Such crowding and confinement factors act to exclude solvent volume from the protein molecules, resulting in an increased local protein concentration and decreased protein entropy. A protein's structure is inherently tied to its function. Examples of processes where crowding and confinement may strongly influence protein function include transmembrane protein dimerization, enzymatic activity, assembly of supramolecular structures (e.g., microtubules), nuclear condensates containing transcriptional machinery, protein aggregation in the contexts of disease and protein therapeutics. Historically, most protein structures have been determined from pure, dilute protein solutions or pure crystals. However, these are not the environments in which these proteins function. Thus, there has been an increased emphasis on analyzing protein structure and dynamics in more "in vivo-like" environments. Complex in vitro models using hydrogel scaffolds to study proteins may better mimic features of the in vivo environment. Therefore, analytical techniques need to be optimized for real-time analysis of proteins within hydrogel scaffolds.

Structure and dynamics of hagfish mucin in different saline environments

The defense mechanism of hagfish against predators is based on its ability to form slime within a few milliseconds. Hagfish slime consists of two main components, namely mucin-like glycoproteins and long protein threads, which together entrap vast amounts of water and thus form a highly dilute hydrogel. Here, we investigate the mucin part of this hydrogel, in particular the role of the saline marine environment on the viscoelasticity and structure. By means of dynamic light scattering (DLS), shear and extensional rheology we probe the diffusion dynamics, the flow behavior, and the longest filament breaking time of hagfish mucin solutions. Using DLS we find a concentration-independent diffusion coefficient - characteristic for polyelectrolytes - up to the entanglement regime of 0.2 mg ml-1, which is about ten times higher than the natural concentration of hagfish mucin in hagfish slime. We also observe a slow relaxation process associated with clustering, probably due to electrostatic interactions. Shear rheology further revealed that hagfish mucin possesses pronounced viscoelastic properties at high concentrations (3 mg ml-1), showing that mucin alone achieves mechanical properties similar to those of natural hagfish slime (mucins and protein threads). The main effects of added seawater salts, and predominantly CaCl2 is to reduce the intensity of the slow relaxation process, which suggests that calcium ions lead to an ionotropic gelation of hagfish mucins.

Self-Assembly of Diphenylalanine-Peptide Nucleic Acid Conjugates

The synthesis and self-assembled nanostructures of a series of nucleopeptides (NPs) derived from the dipeptide Phe-Phe and the peptide nucleic acid unit which are covalently attached through an amide or a triazole linker are described. Depending on the variables such as protecting groups, linkers, and nucleobases, spherical nanoparticles were observed through scanning electron microscopy and high-resolution transmission electron microscopy images, and the porous nature of representative NPs was corroborated by carboxyfluorescein entrapment. Hydrophobic substituents on different sites of NPs and solvents employed for peptide self-assembly played a crucial role for corresponding morphologies. The stability of nanoparticles was also probed under external stimuli such as pH, temperature, and enzymatic hydrolysis using proteolytic enzymes. The semiconducting nature of the NP-modified carbon electrodes suggested their potential use as a new capacitor material.

Treatment of Carious Lesions Using Self-Assembling Peptides

Modern approaches in caries treatment involve lesion management without tissue removal. Regenerative medicine focuses on replacing damaged tissues with biologically similar tissues. This article discusses the scientific evidence and clinical results for self-assembling peptides in modern caries management. The biomimetic remineralization promoted by self-assembling peptide P11-4 has been proven in vitro as an effective therapy for initial caries. P11-4 was rationally designed to promote formation of hydroxyapatite on its surface. The formulation was optimized to ensure the ability of monomeric P11-4 to penetrate past the subsurface lesions and assembly into a biomatrix within. Furthermore, P11-4 has shown that it assembles into fibers within carious lesions, and promotes the remineralization thereof. In a recent clinical study, the safety and efficacy of P11-4 in treatment of initial caries were evaluated. The additional effect of the application of P11-4 (Curodont Repair) was compared to the application of fluoride varnish (Duraphat) alone in active occlusal initial caries lesions on erupting permanent molars. In the 3- and 6-month recalls, the test group showed, both in the laser fluorescence readings and in the clinical assessment of the caries stage and activity, significantly superior lesion regression compared to the control group. No adverse events, medical complications, or allergic reactions related to the treatments were reported. Clinical applicability of treatment was regarded as satisfactory. Patients were happy to receive noninvasive caries treatments. In conclusion, biomimetic mineralization facilitated by P11-4 in combination with fluoride may present a simple, safe, and effective noninvasive treatment for early carious lesions.

Application of the Self- Assembling Peptide P11-4 for Prevention of Acidic Erosion

The aim of this study was to use ultrasonography to evaluate the effect of the self-assembling peptide P11-4 on acid erosion prevention. Curodont Repair (CR), which includes peptide P11-4, was used. Rectangular prisms of bovine enamel (4×1×1 mm) were immersed in pure orange juice for a period of 5 minutes six times per day for 28 days. These samples were divided into four groups of six specimens each and treated differently for an additional period of 28 days: 1) baseline group specimens were stored in artificial saliva; 2) CR group specimens were exposed to curodont without acid challenge; 3) NCRA (no curodont+acid challenge) specimens were treated with orange juice without curodont exposure; and 4) CRA (CR+acid challenge) specimens were treated with curodont before treatment with orange juice. The propagation time of longitudinal ultrasonic velocity (UV) was measured. Ultrastructural observation of each tested enamel surface was carried out using field-emission scanning electron microscopy (SEM). The UV data were analyzed using two-way analysis of variance with time and treatment as confounding factors. Post hoc pairwise tests among groups were performed using the Tukey honestly significant difference test. The average UV in intact bovine enamel for the baseline group ranged from 4,483 to 4,549 m/s and did not vary significantly within the test period. The average ultrasonic velocity (UV) in all samples decreased after the initial erosion. The UV in NCRA decreased further over time. Increased UVs were found for CR and CRA. For CR and CRA, there was no significant difference in UV at the end of the experiment from the initial value before erosion. In the results of SEM observation, the CR and CRA groups had similar morphologic features in that etching patterns were not clearly due to precipitation between the enamel rods. From the results of this in vitro study, it might be concluded that applying enamel matrix derivatives and self-assembling peptides on erosive lesions can improve remineralization.

Injectable network biomaterials via molecular or colloidal self-assembly

Self-assembly is a powerful tool to create functional materials. A specific application for which self-assembled materials are ideally suited is in creating injectable biomaterials. Contrasting with traditional biomaterials that are implanted through surgical means, injecting biomaterials through the skin offers numerous advantages, expanding the scope and impact for biomaterials in medicine. In particular, self-assembled biomaterials prepared from molecular or colloidal interactions have been frequently explored. The strategies to create these materials are varied, taking advantage of engineered oligopeptides, proteins, and nanoparticles as well as affinity-mediated crosslinking of synthetic precursors. Self-assembled materials typically facilitate injectability through two different mechanisms: i) in situ self-assembly, whereby materials would be administered in a monomeric or oligomeric form and self-assemble in response to some physiologic stimulus, or ii) self-assembled materials that, by virtue of their dynamic, non-covalent interactions, shear-thin to facilitate flow within a syringe and subsequently self-heal into its reassembled material form at the injection site. Indeed, many classes of materials are capable of being injected using a combination of these two mechanisms. Particular utility has been noted for self-assembled biomaterials in the context of tissue engineering, regenerative medicine, drug delivery, and immunoengineering. Given the controlled and multifunctional nature of many self-assembled materials demonstrated to date, we project a future where injectable self-assembled biomaterials afford improved practice in advancing healthcare.

Harnessing self-assembled peptide nanoparticles in epitope vaccine design

Vaccination has been one of the most successful breakthroughs in medical history. In recent years, epitope-based subunit vaccines have been introduced as a safer alternative to traditional vaccines. However, they suffer from limited immunogenicity. Nanotechnology has shown value in solving this issue. Different kinds of nanovaccines have been employed, among which virus-like nanoparticles (VLPs) and self-assembled peptide nanoparticles (SAPNs) seem very promising. Recently, SAPNs have attracted special interest due to their unique properties, including molecular specificity, biodegradability, and biocompatibility. They also resemble pathogens in terms of their size. Their multivalency allows an orderly repetitive display of antigens on their surface, which induces a stronger immune response than single immunogens. In vaccine design, SAPN self-adjuvanticity is regarded an outstanding advantage, since the use of toxic adjuvants is no longer required. SAPNs are usually composed of helical or β-sheet secondary structures and are tailored from natural peptides or de novo structures. Flexibility in subunit selection opens the door to a wide variety of molecules with different characteristics. SAPN engineering is an emerging area, and more novel structures are expected to be generated in the future, particularly with the rapid progress in related computational tools. The aim of this review is to provide a state-of-the-art overview of self-assembled peptide nanoparticles and their use in vaccine design in recent studies. Additionally, principles for their design and the application of computational approaches to vaccine design are summarized.

Biomimetic Remineralization of Carious Lesions by Self-Assembling Peptide

Caries is the most common disease in the world. Great efforts have been undertaken for prevention and to identify a regenerative treatment solution for dental caries. Self-assembling β-sheet forming peptides have previously shown to form 3-dimensional fiber networks supporting tissue regeneration. In particular, the self-assembling peptide P₁₁-4 has shown potential in the treatment and prevention of dental caries. It has previously been shown that application of monomeric P₁₁-4 solution to early carious lesions can increase net mineral gain by forming de novo hydroxyapatite crystals. The hypothesis for the mode of action was that monomeric self-assembling peptide P₁₁-4 diffuses into the subsurface lesion body and assembles therein into higher order fibrils, facilitating mineralization of the subsurface volume by mimicking the natural biomineralization of the tooth enamel, and it remains within the lesion body as a scaffold built-in by the newly formed hydroxyapatite. The aim of the present study was to investigate the mechanism of action of the self-assembling peptide P₁₁-4 supporting mineralization of carious enamel. By various analytical methods, it could be shown that the self-assembling peptide P₁₁-4 diffuses into the subsurface lesion, assembles into higher formed aggregates throughout the whole volume of the lesion, and supports nucleation of de novo hydroxyapatite nanocrystals and consequently results in increased mineral density within the subsurface carious lesion. The results showed that the application of self-assembling peptide P₁₁-4 can facilitate the subsurface regeneration of the enamel lesion by supporting de novo mineralization in a similar mode of action as has been shown for the natural formation of dental enamel.

Self-assembled peptide nanostructures for functional materials

Nature is an important inspirational source for scientists, and presents complex and elegant examples of adaptive and intelligent systems created by self-assembly. Significant effort has been devoted to understanding these sophisticated systems. The self-assembly process enables us to create supramolecular nanostructures with high order and complexity, and peptide-based self-assembling building blocks can serve as suitable platforms to construct nanostructures showing diverse features and applications. In this review, peptide-based supramolecular assemblies will be discussed in terms of their synthesis, design, characterization and application. Peptide nanostructures are categorized based on their chemical and physical properties and will be examined by rationalizing the influence of peptide design on the resulting morphology and the methods employed to characterize these high order complex systems. Moreover, the application of self-assembled peptide nanomaterials as functional materials in information technologies and environmental sciences will be reviewed by providing examples from recently published high-impact studies.

Water-Floating Giant Nanosheets from Helical Peptide Pentamers

One of the important challenges in the development of protein-mimetic materials is understanding the sequence-specific assembly behavior and dynamic folding change. Conventional strategies for constructing two-dimensional (2D) nanostructures from peptides have been limited to using β-sheet forming sequences as building blocks due to their natural tendency to form sheet-like aggregations. We have identified a peptide sequence (YFCFY) that can form dimers via a disulfide bridge, fold into a helix, and assemble into macroscopic flat sheets at the air/water interface. Due to the large driving force for 2D assembly and high elastic modulus of the resulting sheet, the peptide assembly induces flattening of the initially round water droplet. Additionally, we found that stabilization of the helix by dimerization is a key determinant for maintaining macroscopic flatness over a few tens of centimeters even with a uniform thickness of <10 nm. Furthermore, the ability to transfer the sheets from a water droplet to another substrate allows for multiple stacking of 2D peptide nanostructures, suggesting possible applications in biomimetic catalysis, biosensors, and 2D related electronic devices.

A structurally self-assembled peptide nano-architecture by one-step electrospinning

Peptide self-assembly during electrospinning while the solvent is evaporating and the fibres are forming.

Treatment of early caries lesions using biomimetic self-assembling peptides--a clinical safety trial

OBJECTIVE

We previously reported that a rationally designed biomimetic self-assembling peptide, P₁₁-4, nucleated hydroxyapatite de novo and was apparently capable of in situ enamel regeneration following infiltration into caries-like lesions. Our present aim was to determine the safety and potential clinical efficacy of a single application of P₁₁-4 on early enamel lesions.

MATERIALS AND METHODS

Fifteen healthy adults with Class V 'white spot' lesions received a single application of P₁₁-4. Adverse events and lesion appearances were recorded over 180 days.

RESULTS

Patients treated with P₁₁-4 experienced a total of 11 adverse events during the study, of which two were possibly related to the protocol. Efficacy evaluation suggested that treatment with P₁₁-4 significantly decreased lesion size (p = 0.02) after 30 days and shifted the apparent progression of the lesions from 'arrested/progressing' to 'remineralising' (p <0.001). A highly significant improvement in the global impression of change was recorded at day 30 compared with baseline (p <0.001).

CONCLUSIONS

The results suggest that treatment of early caries lesions with P₁₁-4 is safe, and that a single application is associated with significant enamel regeneration, presumably by promoting mineral deposition within the subsurface tissue.

Self-assembly characteristics of a structural analogue of Tjernberg peptide

This article aims to understand the pathogenesis behind the formation of amyloid plaques using a modified version of the KLVFF peptide. It was found that the cytotoxicity of the nanostructures formed by the RIVFF peptide may be attributed to the aminoacids with long side chains along with hydrophobic aminoacids resembling the amyloid beta peptide.

Design of self-assembling peptides and their biomedical applications

Combining physics, engineering, chemistry and biology, we can now design, synthesize and fabricate biological nanomaterials at the molecular scale using self-assembling peptide systems. These peptides have been used for fabrication of nanomaterials, including nanofibers, nanotubes and vesicles, nanometer-thick surface coating and nanowires. Some of these peptides are used for stabilizing membrane proteins and drug delivery, and others provide a more permissive environment for 3D cell culture, tissue engineering and repair of tissues in regenerative medicine. Self-assembling peptides are also useful for fabricating a wide spectrum of exquisitely fine architectures, nanomaterials and nanodevices for nanomedicine and nanobiotechnology. These peptide systems lie at the interface between molecular biology, chemistry, materials science and engineering. The studies of designed self-assembling peptides and their applications will help us to understand nature’s enormous power and how to apply it to benefit other disciplines and society.

Interaction of self-assembling beta-sheet peptides with phospholipid monolayers: the role of aggregation state, polarity, charge and applied field

Studies of beta-sheet peptide/phospholipid interactions are important for an understanding of the folding of beta-sheet-rich membrane proteins and the action of antimicrobial and toxic peptides. Further, self-assembling peptides have numerous applications in medicine and therefore an insight is required into the relation between peptide molecular structure and biomembrane activity. We previously developed one of the simplest known model peptide systems which, above a critical concentration (c*) in solution, undergoes nucleated one-dimensional self-assembly from a monomeric random coil into a hierarchy of well defined beta-sheet structures. Here we examine the effects of peptide aggregation, polarity, charge, and applied field on peptide interactions with dioleoyl phosphatidylcholine (DOPC) monolayers using electrochemical techniques. The interactions of six systematically altered 11 residue beta-sheet tape-forming peptides were investigated. The following findings with respect to 11 residue beta-sheet peptide-DOPC interaction arose from the study: (i) The solution monomer peptide species is the monolayer active moeity. (ii) Amphiphilic peptides are more monolayer active than polar peptides in the absence of applied electric field. (iii) Positive charge on amphiphilic peptides facilitates monolayer interaction in the absence of applied electric field. (iv) Negative applied electric field facilitates monolayer interaction with positively charged amphiphilic and polar peptides. (v) Neutral amphiphilic peptides permeabilize DOPC layers to ions to the greatest extent. (vi) The beta-sheet tape forming peptides are shown to be significantly less monolayer disruptive than antimicrobial peptides. These conclusions will greatly contribute to the rational design of new peptide-based biomaterials and biosensors.

Peptide fibrillization

The fibrillization of peptides is relevant to many diseases based on the deposition of amyloids. The formation of fibrils is being intensively studied, especially in terms of nanotechnology applications, where fibrillar peptide hydrogels are used for cell scaffolds, as supports for functional and responsive biomaterials, biosensors, and nanowires. This Review is concerned with fundamental aspects of the self-assembly of peptides into fibrils, and discusses both natural amyloid-forming peptides and synthetic materials, including peptide fragments, copolymers, and amphiphiles.

Surface-assisted assembly of an ionic-complementary peptide: controllable growth of nanofibers

Numerous studies have shown that a surface can direct and regulate molecular assembly. In this study, the nanofiber growth of an ionic-complementary peptide, EAK16-II, on a mica surface was investigated under various solution conditions via in situ atomic force microscopy. In comparison to the assembly in bulk solution, nanofiber growth of EAK16-II on mica is surface-assisted and involves two steps: (1) adsorption of nanofibers and fiber clusters (from the bulk solution) on the surface, serving as the "seeds"; (2) fiber elongation of the "seeds" from their active ends. The nanofiber growth can be controlled by adjusting the solution pH since it modulates the adsorption of the "seeds" on mica and their growth rates. The amount of the adsorbed "seeds" decreases with increasing solution pH, while the growth rate under different solution conditions is found to follow the order pure water > 1 mM HCl > 1 mM NaOH > 10 mM HCl approximately 10 mM NaOH approximately 0. The pH-dependent nanofiber growth is due to the surface charge of the peptides and peptide assemblies in various solutions as indicated by zeta-potential measurements. A simple model was proposed to describe surface-assisted nanofiber growth. This study provides insights into the assembly of peptide/protein on a surface, which is essential to understand such physiological protein aggregation systems as amyloid fibrillogenesis. In addition, the potential of this finding to construct biocompatible electrodes for biomolecular sensing is also discussed.

Dynamic scattering of semirigid macromolecules

The polarized (VV) and depolarized (VH) dynamic light scattering functions of dilute solutions of semirigid macromolecules are calculated assuming that the scattering wave vector [under q] is high compared to the chain Kuhn segment l : ql>>1. The terminal relaxation rate is Gamma proportional to q8/3. Dynamics of both uniaxial and biaxial wormlike macromolecules (filaments) are considered. Biaxial macromolecules are characterized by two persistence lengths proportional to elastic constants for bending in two perpendicular directions (easy and hard bending). We showed that biaxiality may result in a significant broadening of the relaxation spectrum. A nonmonotonous q dependence of the depolarized scattering intensity is predicted. Analyzing the short-time behavior of the dynamic structure factor for t<<1/Gamma, we show that it is characterized by two additional characteristic times: t perpendicular proportional to q(-4) and t parallel proportional to q(-8) reflecting the transverse and the longitudinal dynamics of polymer chains. The longitudinal motions (along the chain contour) increase the initial relaxation rate of the structure factor by a factor of 2. The longitudinal contribution to the dynamic structure factor is significant even for t>>t parallel.

Self-assembling peptide scaffolds promote enamel remineralization

Rationally designed beta-sheet-forming peptides that spontaneously form three-dimensional fibrillar scaffolds in response to specific environmental triggers may potentially be used in skeletal tissue engineering, including the treatment/prevention of dental caries, via bioactive surface groups. We hypothesized that infiltration of caries lesions with monomeric low-viscosity peptide solutions would be followed by in situ polymerization triggered by conditions of pH and ionic strength, providing a biomimetic scaffold capable of hydroxyapatite nucleation, promoting repair. Our aim was to determine the effect of an anionic peptide applied to caries-like lesions in human dental enamel under simulated intra-oral conditions of pH cycling. Peptide treatment significantly increased net mineral gain by the lesions, due to both increased remineralization and inhibition of demineralization over a five-day period. The assembled peptide was also capable of inducing hydroxyapatite nucleation de novo. The results suggest that self-assembling peptides may be useful in the modulation of mineral behavior during in situ dental tissue engineering.

Peptide nanotube-modified electrodes for enzyme-biosensor applications

The fabrication and notably improved performance of composite electrodes based on modified self-assembled diphenylalanine peptide nanotubes is described. Peptide nanotubes were attached to gold electrodes, and we studied the resulting electrochemical behavior using cyclic voltammetry and chronoamperometry. The peptide nanotube-based electrodes demonstrated a direct and unmediated response to hydrogen peroxide and NADH at a potential of +0.4 V (vs SCE). This biosensor enables a sensitive determination of glucose by monitoring the hydrogen peroxide produced by an enzymatic reaction between the glucose oxidase attached to the peptide nanotubes and glucose. In addition, the marked electrocatalytic activity toward NADH enabled a sensitive detection of ethanol using ethanol dehydrogenase and NAD+. The peptide nanotube-based amperometric biosensor provides a potential new tool for sensitive biosensors and biomolecular diagnostics.

TiO2 Sphere-Tube-Fiber Transition Induced by Oligovaline Concentration Variation

L-Valine-based oligopeptides with the general structure Z-(L-Val)(n)-OMe or -OH (n = 1-4) form stable organogels in a variety of solvents, including the inorganic liquid tetraethylorthosilicate. The acid form Z-(L-Val)(n)-OH is a less efficient gelator than the methyl ester, but forms stable organogels in aromatic solvents and di- and trichloromethane. In all cases the peptides form micrometer long helical fibers with a beta-sheet structure. IR and X-ray diffraction show that the peptides have closely related structures in the crystalline state and the fibers in the organogels. The gels are efficient templates for the fabrication of complex titania architectures on a (sub)micron length scale: at low peptide concentrations titania spheres form and at higher concentrations one-dimensional shapes like hollow titania tubes or titania fibers are observed. The tubes are stable towards calcination whereas the fibers (partially) transform into spherical or even bulk particles.

Electrochemical screening of self-assembling β-sheet peptides using supported phospholipid monolayers

In the context of the medical applications of beta-sheet self-assembling peptides, it is important to be able to predict their activity at the biological membrane level. A study of the interaction of four systematically varied 11-residue (P11-1, P11-2, P11-6 and P11-7) and one 13-residue (P13-1) designed beta-sheet self-assembling peptides with DOPC monolayers on a mercury electrode is reported in this paper. Experiments were carried out in 0.1 mol dm(-3) KCl electrolyte with added phosphate buffer (0.001 mol dm(-3)) at pH approximately 7.6. The capacity-potential curves of the coated electrode in the presence and absence of the different peptides were measured using out-of-phase ac voltammetry. The frequency dependence of the complex impedance of the coated electrode surfaces in the presence and absence of the peptides was estimated between 65,000 and 0.1 Hz at -0.4V versus Ag/AgCl 3.5 mol(-3) dm(-3) KCl. The monolayer permeabilising properties of the peptides were studied by following the reduction of Tl(I) to Tl(Hg) at the coated electrode. Of the five peptides studied, P11-2, P11-7 and P13-1 interact most strongly with the DOPC layer. P11-1 which has a polar primary structure shows no obvious interaction with the phospholipid but surprisingly, it permeabilises the phospholipid layer to Tl(+).

Atomic structures of peptide self-assembly mimics

Although the beta-rich self-assemblies are a major structural class for polypeptides and the focus of intense research, little is known about their atomic structures and dynamics due to their insoluble and noncrystalline nature. We developed a protein engineering strategy that captures a self-assembly segment in a water-soluble molecule. A predefined number of self-assembling peptide units are linked, and the beta-sheet ends are capped to prevent aggregation, which yields a mono-dispersed soluble protein. We tested this strategy by using Borrelia outer surface protein (OspA) whose single-layer beta-sheet located between two globular domains consists of two beta-hairpin units and thus can be considered as a prototype of self-assembly. We constructed self-assembly mimics of different sizes and determined their atomic structures using x-ray crystallography and NMR spectroscopy. Highly regular beta-sheet geometries were maintained in these structures, and peptide units had a nearly identical conformation, supporting the concept that a peptide in the regular beta-geometry is primed for self-assembly. However, we found small but significant differences in the relative orientation between adjacent peptide units in terms of beta-sheet twist and bend, suggesting their inherent flexibility. Modeling shows how this conformational diversity, when propagated over a large number of peptide units, can lead to a substantial degree of nanoscale polymorphism of self-assemblies.

Biomimetic self-assembling peptides as injectable scaffolds for hard tissue engineering

The production of bone-, dentine- and enamel-like biomaterials for the engineering of mineralized (hard) tissues is a high-priority in regenerative medicine and dentistry. An emerging treatment approach involves the use of short biomimetic peptides that self-assemble to form micrometer-long nanofibrils with well defined surface chemistry and periodicity that display specific arrays of functional groups capable of mineral nucleation. The fibrils also give rise to dynamically stable 3D scaffold gels for the potential control of crystal disposition and growth. Peptides can also be injected in their monomeric fluid state, with subsequent self-assembly and gelation in situ triggered by physiological conditions. In this way, they can infiltrate and self-assemble within irregular or microscopic cavities, for restorative treatment of bone defects, dentinal hypersensitivity or dental decay. Cell adhesion and proliferation is also supported by these scaffolds, offering further advantages for applications in hard tissue engineering. These self-assembling matrices also provide well defined model systems that can contribute greatly to the elucidation of the biological mechanisms of protein-mediated biomineralization.

Structure of core domain of fibril-forming PHF/Tau fragments

Short peptide sequences within the microtubule binding domain of the protein Tau are proposed to be core nucleation sites for formation of amyloid fibrils displaying the paired helical filament (PHF) morphology characteristic of neurofibrillary tangles. To study the structure of these proposed nucleation sites, we analyzed the x-ray diffraction patterns from the assemblies formed by a variety of PHF/tau-related peptide constructs containing the motifs VQIINK (PHF6*) in the second repeat and VQIVYK (PHF6) in the third repeat of tau. Peptides included: tripeptide acetyl-VYK-amide (AcVYK), tetrapeptide acetyl-IVYK-amide (AcPHF4), hexapeptide acetyl-VQIVYK-amide (AcPHF6), and acetyl-GKVQIINKLDLSNVQKDNIKHGSVQIVYKPVDLSKVT-amide (AcTR4). All diffraction patterns showed reflections at spacings of 4.7 A, 3.8 A, and approximately 8-10 A, which are characteristic of an orthogonal unit cell of beta-sheets having dimensions a=9.4 A, b=6.6 A, and c=approximately 8-10 A (where a, b, and c are the lattice constants in the H-bonding, chain, and intersheet directions). The sharp 4.7 A reflections indicate that the beta-crystallites are likely to be elongated along the H-bonding direction and in a cross-beta conformation. The assembly of the AcTR4 peptide, which contains both the PHF6 and PHF6* motifs, consisted of twisted sheets, as indicated by a unique fanning of the diffuse equatorial scattering and meridional accentuation of the (210) reflection at 3.8 A spacing. The diffraction data for AcVYK, AcPHF4, and AcPHF6 all were consistent with approximately 50 A-wide tubular assemblies having double-walls, where beta-strands constitute the walls. In this structure, the peptides are H-bonded together in the fiber direction, and the intersheet direction is radial. The positive-charged lysine residues face the aqueous medium, and tyrosine-tyrosine aromatic interactions stabilize the intersheet (double-wall) layers. This particular contact, which may be involved in PHF fibril formation, is proposed here as a possible aromatic target for anti-tauopathy drugs.

The internal dynamic modes of charged self-assembled peptide fibrils

Photon correlation spectroscopy is used to study the internal dynamics of self-assembled charged peptide fibrils. Short neutral and charged polymeric aggregates have diffusive modes due to whole macromolecular motion. For long semiflexible fibrils the logarithm of the intermediate scattering function follows a q(2)t(3/4) scaling at long times consistent with a Kratky-Porod free energy and preaveraged Oseen hydrodynamics. Persistence lengths on the order of micrometers are calculated for the peptide fibrils consistent with estimates from the liquid-crystalline phase behavior. Fibril diameters (5-35 nm) calculated from the initial decay of the correlation functions are in agreement with transmission electron microscopy measurements.

Structure and dynamics of polymer-grafted clay suspensions

The structure and dynamics of polymer-grafted two-dimensional silicate layers in solution were investigated. The geometry of the individual silicate layers was examined by looking at both polarized and depolarized light scattering from dilute solutions, while higher-concentration systems were used to study the interaction and dynamics of polymer-grafted silicate layers in suspension. The form factor for an oblate ellipsoid was used to fit the polarized intensity profile, and values of a approximately 80 nm and b approximately 380 nm for the semi-axes were obtained. The 80 nm value compares reasonably with the dimensions of the polymer brushes grafted on the surface of the silicate layers. The modulus of the grafted silicate in solution, as determined by Brillouin scattering, is of the order of 10 GPa. The cooperative diffusion mechanism, typical of interacting polymer chains, is suppressed due to the high polymer osmotic pressure. The osmotic pressure is also responsible for the weak interpenetration of the densely grafted polymer chains on the surface of the silicate layers. The scattering data indicates that the polymer-grafted nanoparticles move via collective diffusion and experience significant decrease in mobility above their overlap concentration.

Novel electrochemical biosensing platform using self-assembled peptide nanotubes

Here we describe a novel electrochemical biosensing platform based on biocompatible, well-ordered, self-assembled diphenylalanine peptide nanotubes. Voltammetric and time-based amperometric techniques were applied to demonstrate the ability of the peptide nanotubes to improve the electrochemical parameters of graphite electrodes. The findings clearly show that this novel class of peptide nanotubes provides an attractive component for future electroanalytical devices.

The mechanism of amyloid spherulite formation by bovine insulin

The formation of amyloid-containing spherulite-like structures has been observed in some instances of amyloid diseases, as well as in amyloid fibril-containing solutions in vitro. In this article we describe the structure and kinetics of bovine insulin amyloid fibril spherulites formed in the presence and absence of different salts and at different salt concentrations. The general spherulite structure consists of radially oriented amyloid fibrils, as shown by optical microscopy and environmental scanning electron microscopy. In the center of each spherulite, a "core" of less regularly oriented material is observed, whose size decreases when the spherulites are formed in the presence of increasing concentrations of NaCl. Similarly, amyloid fibrils form faster in the presence of NaCl than in its absence. A smaller enhancement of the rate of formation with salt concentration is observed for spherulites. These data suggest that both amyloid fibril formation and random aggregation occur concurrently under the conditions tested. Changes in their relative rates result in the different-sized cores observed in the spherulites. This mechanism can be likened to that leading to the formation of spherulites of polyethylene, in agreement with observations that polypeptide chains under partially denaturing conditions can exhibit behavior not dissimilar to that of synthetic polymers.

Light-Scattering Study of the Aggregation of Syndiotactic Poly(methyl methacrylate) in Solution

Syndiotactic poly(methyl methacrylate (s-PMMA) may undergo aggregation in n-butyl chloride (n-BuCl) at temperatures below the theta temperature. The aggregation behavior of the s-PMMA with weight-average molecular weight M(w) =6.06 x 10(5) g mol(-1) was studied by a combination of static and dynamic laser-light-scattering experiments. A solution of concentration 1.12 x 10(-4) g mL(-1) was quenched from 50 degrees C (above the theta temperature in n-BuCl, 35 degrees C to 12 degrees C, and the aggregation process was measured over 60 h. The time dependence of M(w) the root-mean-square z-average radius of gyration < R(g) >, and the average hydrodynamic radius <R(h)> were used to monitor the growth of the aggregates, with the result M(w) approximately < R(g) > d(f) (where d(f) = 1.98 +/- 0.02), which implies the formation of a fractal aggregate. The observed fractal dimension, d(f), is close to that expected for a reaction-limited cluster aggregation for which d(f) = 2.1. In addition, atomic force microscopy was used to image the aggregates.

The formation of spherulites by amyloid fibrils of bovine insulin

Bovine insulin has long been known to self-assemble in vitro into amyloid fibrils. We have observed a further higher-order self-association of the protein into spherical structures, with diameters typically around 50 microm but ranging from 10 to 150 microm. In a polarizing light microscope, these structures exhibit a "Maltese-cross" extinction pattern typical of spherulites. Spherical structures of a similar size distribution can be observed in the environmental scanning electron microscope, which also reveals the presence of significant amounts of water in the structures. The spherulites contain a large quantity of well defined amyloid fibrils, suggesting that they are formed at least in part as a consequence of the self-assembly of preformed fibrils. Similar structures also have been observed in the tissues of patients suffering from amyloid disorders. The ability of amyloid fibrils to form such higher-order assemblies supports the hypothesis that they represent a generic form of polypeptide structure with properties that are analogous to those of classical synthetic polymers.

Aqueous gel formation of a synthetic peptide derived from the beta-sheet domain of platelet factor-4

We observed gelation of a 23-residue peptide derived from the beta-sheet domain of platelet factor-4 (PF4(24)(-)(46)). The gels were primarily heterogeneous mixtures of 50-200 microm spherical aggregates in a less-dense gel matrix. Infrared and circular dichroism spectroscopies showed gelation involving the conversion of PF4(24)(-)(46) from random coil to beta-sheet. We used aggregation-induced NMR resonance broadening to show that temperature, pH, and ionic strength influenced PF4(24)(-)(46) gelation rates. Under identical solution conditions, gel formation took days at T </= 20 degrees C but only 30 min at T >/= 50 degrees C. Gelation was most rapid at pH values near the pK(a) of the central His35 residue. Increases in solution ionic strength reduced the critical gelation concentration of PF4(24)(-)(46). Our results suggest that PF4(24)(-)(46) gels by a process combining aspects of both heat-set and beta-fibril gelation mechanisms.