Coassembly in binary mixtures of peptide amphiphiles containing oppositely charged residues

Electrostatic assembly of a multicomponent peptide/amphiphile nanotube

The ability to integrate the elements of a multicomponent nanostructure with nanoscale precision by co-assembly provides a versatile strategy to create novel materials with tunable properties. The search for function in these materials will require new strategies to be developed that control the assembly process, especially for structurally dissimilar components, which often have a propensity to self-sort into non-integrated nanostructures. In this work, two components, a peptide (1) and an amphiphile (2), were integratively co-assembled into a multicomponent nanotube. The interaction between the two components at the supramolecular level was driven by the electrostatic complementarity of the components, which was controlled by the pH-dependent charge of 1. Characterization of the co-assembled nanotube, 1-2NT, was achieved using a combination of TEM, AFM, CLSM and SIM techniques, which showed that both components were colocalized within the nanotube. These studies, in conjunction with CD, IR and fluorescence studies, suggested that 1 and 2 were arranged in partially reorganized, self-sorted domains, which were integrated as laminated nanoribbons that coiled together into the final co-assembled nanotube.

An Offset Patterned Cross-β Structure in Assemblies of C3 -Symmetric Peptide Amphiphiles

Developing peptide-based materials with controlled morphology is a critical theme of soft matter research. Herein, we report the formation of a novel, patterned cross-β structure formed by self-assembled C3 -symmetric peptide amphiphiles based on diphenylalanine and benzene-1,3,5-tricarboxamide (BTA). The cross-β motif is an abundant structural element in amyloid fibrils and aggregates of fibril-forming peptides, including diphenylalanine. The incorporation of topological constraints on one edge of the diphenylalanine fragment limits the number of β-strands in β-sheets and leads to the creation of an unconventional offset-patterned cross-β structure consisting of short 3×2 parallel β-sheets stabilized by phenylalanine zippers. In the reported assembly, two patterned cross-β structures bind parallel arrays of BTA stacks in a superstructure within a single-molecule-thick nanoribbon. In addition to a threefold network of hydrogen bonds in the BTA stack, each molecule becomes simultaneously bound by hydrogen bonds from three β-sheets and four phenylalanine zippers. The diffuse layer of alkyl chains with terminal polar groups prevents the nanoribbons from merging and stabilizes cross-β-structure in water. Our results provide a simple approach to the incorporation of novel patterned cross-β motifs into supramolecular superstructures and shed light on the general mechanism of β-sheet formation in C3 -symmetric peptide amphiphiles.

Supramolecular self-assembled peptide-engineered nanofibers: A propitious proposition for cancer therapy

Cancer is a devastating disease that causes a substantial number of deaths worldwide. Current therapeutic interventions for cancer include chemotherapy, radiation therapy, or surgery. These conventional therapeutic approaches are associated with disadvantages such as multidrug resistance, destruction of healthy tissues, and tissue toxicity. Therefore, there is a paradigm shift in cancer management wherein nanomedicine-based novel therapeutic interventions are being explored to overcome the aforementioned disadvantages. Supramolecular self-assembled peptide nanofibers are emerging drug delivery vehicles that have gained much attention in cancer management owing to their biocompatibility, biodegradability, biomimetic property, stimuli-responsiveness, transformability, and inherent therapeutic property. Supramolecules form well-organized structures via non-covalent linkages, the intricate molecular arrangement helps to improve tissue permeation, pharmacokinetic profile and chemical stability of therapeutic agents while enabling targeted delivery and allowing efficient tumor imaging. In this review, we present fundamental aspects of peptide-based self-assembled nanofiber fabrication their applications in monotherapy/combinatorial chemo- and/or immuno-therapy to overcome multi-drug resistance. The role of self-assembled structures in targeted/stimuli-responsive (pH, enzyme and photo-responsive) drug delivery has been discussed along with the case studies. Further, recent advancements in peptide nanofibers in cancer diagnosis, imaging, gene therapy, and immune therapy along with regulatory obstacles towards clinical translation have been deliberated.

Small-angle scattering techniques for peptide and peptide hybrid nanostructures and peptide-based biomaterials

The use of small-angle scattering (SAS) in the study of the self-assembly of peptides and peptide conjugates (lipopeptides, polymer-peptide conjugates and others) is reviewed, highlighting selected research that illustrates different methods and analysis techniques. Both small-angle x-ray scattering (SAXS) and small-angle neutron scattering (SANS) are considered along with examples that exploit their unique capabilities. For SAXS, this includes the ability to perform rapid measurements enabling high throughput or fast kinetic studies and measurements under dilute conditions. For SANS, contrast variation using H2O/D2O mixtures enables the study of peptides interacting with lipids and TR-SANS (time-resolved SANS) studies of exchange kinetics and/or peptide-induced structural changes. Examples are provided of studies measuring form factors of different self-assembled structures (micelles, fibrils, nanotapes, nanotubes etc) as well as structure factors from ordered phases (lyotropic mesophases), peptide gels and hybrid materials such as membranes formed by mixing peptides with polysaccharides or peptide/liposome mixtures. SAXS/WAXS (WAXS: wide-angle x-ray scattering) on peptides and peptide hybrids is also discussed, and the review concludes with a perspective on potential future directions for research in the field.

Engineering β-Sheet Peptide Coassemblies for Biomaterial Applications

Peptide coassembly, wherein at least two different peptides interact to form multicomponent nanostructures, is an attractive approach for generating functional biomaterials. Current efforts seek to design pairs of peptides, A and B, that form nanostructures (e.g., β-sheets with ABABA-type β-strand patterning) while resisting self-assembly (e.g., AAAAA-type or BBBBB-type β-sheets). To confer coassembly behavior, most existing designs have been based on highly charged variants of known self-assembling peptides; like-charge repulsion limits self-assembly while opposite-charge attraction promotes coassembly. Recent analyses using solid-state NMR and coarse-grained simulations reveal that preconceived notions of structure and molecular organization are not always correct. This perspective highlights recent advances and key challenges to understanding and controlling peptide coassembly.

Ordered Packing of β-Sheet Nanofibrils into Nanotubes: Multi-hierarchical Assembly of Designed Short Peptides

Although it is well-known proteins and their complexes are hierarchically organized and highly ordered structures, it remains a major challenge to replicate their hierarchical self-assembly process and to fabricate multihierarchical architectures with well-defined shapes and monodisperse characteristic sizes via peptide self-assembly. Here we describe an amphiphilic short peptide Ac-I₃GGHK-NH₂ that first preassembles into thin, left-handed β-sheet nanofibrils, followed by their ordered packing into right-handed nanotubes. The key intermediate morphology and structures featuring the hierarchical process are simultaneously demonstrated. Further mechanistic exploration with the variants Ac-I₃GGGK-NH₂, Ac-I₃GGFK-NH₂, and Ac-I₃GG^DH^DK-NH₂ reveals the vital role of multiple His-His side chain interactions between nanofibrils in mediating higher-order assembly and architectures. Altogether, our findings not only advance current understanding of hierarchical assembly of peptides and proteins but also afford a paradigm of how to take advantage of side chain interactions to construct higher-order assemblies with enhanced complexities.

Self-Assembly of Angiotensin-Converting Enzyme Inhibitors Captopril and Lisinopril and Their Crystal Structures

The peptide angiotensin-converting enzyme inhibitors captopril and lisinopril are unexpectedly shown to exhibit critical aggregation concentration (CAC) behavior through measurements of surface tension, electrical conductivity, and dye probe fluorescence. These three measurements provide similar values for the CAC, and there is also evidence from circular dichroism spectroscopy for a possible conformational change in the peptides at the same concentration. Cryogenic transmission electron microscopy indicates the formation of micelle-like aggregates above the CAC, which can thus be considered a critical micelle concentration, and the formation of aggregates with a hydrodynamic radius of ∼6-7 nm is also evidenced by dynamic light scattering. We also used synchrotron radiation X-ray diffraction to determine the single-crystal structure of captopril and lisinopril. Our results improve the accuracy of previous data reported in the literature, obtained using conventional X-ray sources. We also studied the structure of aqueous solutions containing captopril or lisinopril at high concentrations. The aggregation may be driven by intermolecular interactions between the proline moiety of captopril molecules or between the phenylalanine moiety of lisinopril molecules.

Synthesis and characterization of mono S-lipidated peptide hydrogels: a platform for the preparation of reactive oxygen species responsive materials

In this work we report the synthesis of mono lipidated peptides containing a 3-mercaptopropionate linker in the N-terminus by means of a photoinitiated thiol-ene reaction (S-lipidation). We evaluate the self-assembling and hydrogelation properties of a library of mono S-lipidated peptides containing lipid chains of various lengths and demonstrate that hydrogelation was driven by a balance between the lipid chain's hydrophobicity and the peptide's facial hydrophobicity. We further postulate that a simple calculation using estimated values of log D could be used as a predictor of hydrogelation when designing similar systems. A mono S-lipidated peptide containing a short lipid chain that formed hydrogels was fully characterized and a mechanism for the peptide hydrogelation developed. Finally, we demonstrate that the presence of the thioether group in the mono S-lipidated peptide hydrogels, which is a feature lacking in conventional N-acyl lipidated systems, enables the controlled disassembly of the gel via oxidation to the sulfoxide by reactive oxygen species in accordance with a hydrophobicity-modulated strategy. Thus, we conclude that mono S-lipidated peptide hydrogels constitute a novel and simple tool for the development of tissue engineering and targeted drug delivery applications of diseases with overexpression of reactive oxygen species (e.g. degenerative and metabolic diseases, and cancers).

SAPdb: A database of short peptides and the corresponding nanostructures formed by self-assembly

Nanostructures generated by self-assembly of peptides yield nanomaterials that have many therapeutic applications, including drug delivery and biomedical engineering, due to their low cytotoxicity and higher uptake by targeted cells owing to their high affinity and specificity towards cell surface receptors. Despite the promising implications of this rapidly expanding field, there is no dedicated resource to study peptide nanostructures. This study endeavours to create a repository of short peptides, which may prove to be the best models to study ordered nanostructures formed by peptide self-assembly. SAPdb has a repertoire of 1049 entries of experimentally validated nanostructures formed by the self-assembly of small peptides. It consists of 328 tripeptides, 701 dipeptides, and 20 single amino acids with some conjugate partners. Each entry encompasses comprehensive information about the peptide, such as chemical modifications, the type of nanostructure formed, experimental conditions like pH, temperature, solvent required for the self-assembly, etc. Our analysis indicates that peptides containing aromatic amino acids favour the formation of self-assembling nanostructures. Additionally, we observed that these peptides form different nanostructures under different experimental conditions. SAPdb provides this comprehensive information in a hassle-free tabulated manner at a glance. User-friendly browsing, searching, and analysis modules have been integrated for easy data retrieval, data comparison, and examination of properties. We anticipate SAPdb to be a valuable repository for researchers engaged in the burgeoning arena of nanobiotechnology. It is freely available at https://webs.iiitd.edu.in/raghava/sapdb.

Coassembly of C13-Dipeptides: Gelations from Solutions and Precipitations

C₁₃-dipeptides that did not gel on their own were found to form hydrogels when combined with mixtures (coassembly). At pH = 4.6, by mixing negatively charged C₁₃-WD (C₁₃-WD^2- and/or C₁₃-WD^-) with C₁₃-KW or C₁₃-YK, where the side chain of K carried positive charge, two composite hydrogels with different mechanical properties were formed. The gels exhibited various fiber structures that would account for their individual functionalities. According to molecular dynamics computer simulations, the composite systems formed spherical micelles through hydrophobic interactions that further aggregate to form gels through electrostatic interactions. The electrostatic repulsions between C₁₃-WD molecules were interfered by insertions of C₁₃-KW or C₁₃-YK molecules, which result in gel formation in the composite systems. The results of computer simulations well explained the experimental observations, which provided new insights into the design and selection strategies for peptide gelators.

Recent Progress in Ionic Coassembly of Cationic Peptides and Anionic Species

Peptide assembly has been extensively exploited as a promising platform for the creation of hierarchical nanostructures and tailor-made bioactive materials. Ionic coassembly of cationic peptides and anionic species is paving the way to provide particularly important contribution to this topic. In this review, the recent progress of ionic coassembly soft materials derived from the electrostatic coupling between cationic peptides and anionic species in aqueous solution is systematically summarized. The presentation of this review starts from a brief background on the general importance and advantages of peptide-based ionic coassembly. After that, diverse combinations of cationic peptides with small anions, macro- and/or oligo-anions, anionic polymers, and inorganic polyoxometalates are described. Emphasis is placed on the hierarchical structures, value-added properties, and applications. The molecular design of cationic peptides and the general principles behind the ionic coassembled structures are discussed. It is summarized that the combination of interesting and unique characteristics that arise both from the chemical diversity of peptides and the wide range of anionic species may contribute in a variety of output, including drug delivery, tissue engineering, gene transfection, and antibacterial activity. The emergent new phenomena and findings are illustrated. Finally, the outlook for the peptide-based ionic coassembly systems is also presented.

Aligned Assembly in a 2-D Gel of a Water-Soluble Peptide

We demonstrate the assembly of a compact, gel-like Langmuir-Blodgett film of rods formed by self-assembly of a β-sheet-forming water-soluble peptide, Ac-IKHLSVN-NH₂, at the surface of aqueous electrolytes. We characterize surface pressure hysteresis and demonstrate shear stiffening of the surface caused by area cycling, which we interpret as due to rearrangement and alignment of the rods. We show strong effects of the electrolyte on the assembly of the elementary rods, which can be related to the Hofmeister series and interpreted by effects on the interaction energies mediated by ions and water. Formation of β-sheet structures and assembly of these into surface-segregated semicrystalline gels was strongly promoted by ammonium sulfate electrolyte. With ammonium sulfate electrolyte as subphase for Langmuir-Blodgett film deposition, shear stiffening by surface area cycling resulted in very compact films on transfer to a substrate.

Nanoribbon self-assembly and hydrogel formation from an NOctanoyl octapeptide derived from the antiparallel β-Interface of a protein homotetramer

The effect of installing different lipid chains (C₆, C₈, C₁₀, and C₁₆) on the N-terminus of an octapeptide derived from the antiparallel β-interface of the diaminopimelate decarboxylase protein homotetramer has been investigated. Notably, the C₈ peptide conjugate assembled into wide twisted nanoribbons and formed hydrogels, which to the best of our knowledge constitutes the first example of a peptide containing an eight carbon alkyl chain that demonstrates these properties, a space typically occupied by peptide amphiphiles with long lipid chains. Furthermore, this self-assembling lipopeptide exhibited pH and temperature stability with shear thinning properties suitable for biomedical applications. Importantly, in this work the application of the polystyrene-based sorbent Diaion™ HP20SS for the simple large-scale purification of self-assembling peptides is presented as an alternative to the use of time-consuming and labor-intensive reverse-phase high-performance liquid chromatography. STATEMENT OF SIGNIFICANCE: Peptides that can self-assemble into defined nanostructures are highly attractive for many biomedical applications given their unique physical and chemical properties. It is recognized that self-assembling peptides derived from naturally occurring proteins offer an unlimited source of functionalities and structures, which are hard to uncover with designed sequences. In this study, we have investigated the effect of installing different lipids chains on the N-terminus of an octapeptide derived from the antiparallel β-interface of the diaminopimelate decarboxylase protein homo tetramer. We also reported the use of polymeric Diaion^Ⓡ HP20SS beads as an alternative solid support to purify self-assembling peptides.

A Comprehensive Study on Self-Assembly and Gelation of C13-Dipeptides-From Design Strategies to Functionalities

Computational and experimental methods were applied to investigate the self-assembly and gelation of C₁₃-dipeptides. A modified aggregation propensity (AP_S) was introduced to correlate the effects of side chains of amino acids on the tendency to aggregate. From the experimental results, the ranges of 0.156 < AP_S < 0.250 seemed to be a proper region for the C₁₃-dipeptides to form hydrogels, while other molecules with higher or lower AP_S were insoluble or dissociated. As observed from molecular dynamics simulations, the C₁₃-dipeptides first formed small aggregates through hydrophobic interactions and then rearranged through electrostatic attractions and hydrogen bonds for self-assembly. The C₁₃-dipeptides tended to be antiparallel packed, as shown by hydrogen bonding analyses. Experimental observations and analyses on the structures of C₁₃-dipeptide hydrogels matched the computational conclusions very well. From the five selected gelators, i.e., C₁₃-GW, C₁₃-VY, and C₁₃-WT, strong π-π stacking was observed. For C₁₃-WS, strong hydrogen bonding was found, and in C₁₃-WY, both strong π-π interactions and hydrogen bonds were found. It takes around 90 min or longer for C₁₃-dipeptides to form hydrogels, and those formed by C₁₃-WY and C₁₃-WS had weak water holding capacities, which might be due to strong intermolecular hydrogen bonding. From rheological studies, the C₁₃-dipeptides formed strong chemical gels that were stabilized by strong interactions between the molecular aggregates. These gelators exhibit the potentials to be environmentally friendly substitutes for the common functionalized peptide gelators.

Secondary structure of end group functionalized oligomeric-l-lysines: investigations of solvent and structure dependent helicity

Fibrillation of supramolecular building blocks represents an important model system for complex proteins and peptides, such as amyloidogenic proteins, displaying aggregation and subsequent collapse of their biological functions. In this work, we synthesized narrow-dispersed, end group-telechelic, oligomeric-(l-lysine(carboxybenzyl (Z)/trifluoroacetyl (TFA))) n s (n = 3-33) as a model system for studying assembly and secondary structure formation, prepared via ring opening polymerization (ROP) of N-carboxyanhydrides (NCA). Our primary goal was to understand the influence of amino acid chain length and end group-modification on the secondary structure and fibrillation of the oligo-Z/TFA-protected lysines. Synthesis was accomplished by initiation of ROP with 11-amino-undecene, followed by complete chain end functionalization reactions of the N-terminus by 10-undecenoyl-chloride. The so obtained oligomeric-(l-lysine(Z/TFA)) n s were fractionated according to their number of repeating units (n) with preparative GPC using DMF as the eluent. As proven by MALDI-ToF MS, 1H-NMR-spectroscopy and analytical GPC, they were separated into fractions with low polydispersity (Đ) values, ranging from 1.02-1.08. Secondary structural investigations of these narrowly-dispersed oligomeric-(l-lysine(Z/TFA)) n s (n = 33 ± 6, n = 18 ± 6, n = 12 ± 4, n = 5 ± 2) were accomplished by CD spectroscopy in TFE and HFIP, indicating that TFE was able to induce/stabilize the formation of α-helicity. Fibril formation of oligomeric-(l-lysine(Z/TFA)) n s with shorter chain lengths (n = 7 and n = 3) were chosen to investigate the effect of the number of repeating units' role on the self-assembly of the oligomers in TFE. TEM images of these selected fractions, f19 with n = 7 and f28 with n = 3, showed that fibrillization occured and the formation of a dense fibrillar mesh was observed when the amino acid chain length is equal to 7. Therefore, the influences of the number of repeating units (n), end-group functionalities (mono- or bis-functional) and the choice of solvents (TFE or HFIP) on the propensity to form helical structure allowed us to calibrate their secondary structure.

Down-regulating Proteolysis to Enhance Anticancer Activity of Peptide Nanofibers

Nanofibers of short peptides are emerging as a promising type of agents for inhibiting cancer cells. But the proteolysis of peptides decreases the anticancer efficacy of the peptide nanofibers. Here we show that decreasing the activity of proteasomes enhance the activity of peptide nanofibers for inhibiting cancer cells. Based on the structure of galactin-3, we designed a heptapeptide, which self-assembles to form nanofibers. The nanofibers of the heptapeptide exhibit moderate cytotoxicity to three representative cancer cell lines (HeLa, MCF-7, and HepG2), largely due to the proteolysis of the peptides. Using a clinically approved proteasome inhibitor, bortezomib, to treat the cancer cells significantly decreases the proteolysis of the peptides and enhances the activity of the peptide nanofibers for inhibiting the cancer cells. This work illustrates a promising approach for enhancing the anticancer efficacy of peptide nanofibers by modulating intracellular protein degradation machinery, as well as provides insights for understanding the cytotoxicity of aberrant protein or peptide aggregates in complicated cellular environment.

Force and time-dependent self-assembly, disruption and recovery of supramolecular peptide amphiphile nanofibers

Biological feedback mechanisms exert precise control over the initiation and termination of molecular self-assembly in response to environmental stimuli, while minimizing the formation and propagation of defects through self-repair processes. Peptide amphiphile (PA) molecules can self-assemble at physiological conditions to form supramolecular nanostructures that structurally and functionally resemble the nanofibrous proteins of the extracellular matrix, and their ability to reconfigure themselves in response to external stimuli is crucial for the design of intelligent biomaterials systems. Here, we investigated real-time self-assembly, deformation, and recovery of PA nanofibers in aqueous solution by using a force-stabilizing double-pass scanning atomic force microscopy imaging method to disrupt the self-assembled peptide nanofibers in a force-dependent manner. We demonstrate that nanofiber damage occurs at tip-sample interaction forces exceeding 1 nN, and the damaged fibers subsequently recover when the tip pressure is reduced. Nanofiber ends occasionally fail to reconnect following breakage and continue to grow as two individual nanofibers. Energy minimization calculations of nanofibers with increasing cross-sectional ellipticity (corresponding to varying levels of tip-induced fiber deformation) support our observations, with high-ellipticity nanofibers exhibiting lower stability compared to their non-deformed counterparts. Consequently, tip-mediated mechanical forces can provide an effective means of altering nanofiber integrity and visualizing the self-recovery of PA assemblies.

Multicomponent peptide assemblies

Self-assembled peptide nanostructures have been increasingly exploited as functional materials for applications in biomedicine and energy. The emergent properties of these nanomaterials determine the applications for which they can be exploited. It has recently been appreciated that nanomaterials composed of multicomponent coassembled peptides often display unique emergent properties that have the potential to dramatically expand the functional utility of peptide-based materials. This review presents recent efforts in the development of multicomponent peptide assemblies. The discussion includes multicomponent assemblies derived from short low molecular weight peptides, peptide amphiphiles, coiled coil peptides, collagen, and β-sheet peptides. The design, structure, emergent properties, and applications for these multicomponent assemblies are presented in order to illustrate the potential of these formulations as sophisticated next-generation bio-inspired materials.

Methods to Characterize the Nanostructure and Molecular Organization of Amphiphilic Peptide Assemblies

Methods to characterize the nanostructure and molecular organization of aggregates of peptides such as amyloid or amphiphilic peptide assemblies are reviewed. We discuss techniques to characterize conformation and secondary structure including circular and linear dichroism and FTIR and Raman spectroscopies, as well as fluorescence methods to detect aggregation. NMR spectroscopy methods, especially solid-state NMR measurements to probe beta-sheet packing motifs, are also briefly outlined. Also discussed are scattering methods including X-ray diffraction and small-angle scattering techniques including SAXS (small-angle X-ray scattering) and SANS (small-angle neutron scattering) and dynamic light scattering. Imaging methods are direct methods to uncover features of peptide nanostructures, and we provide a summary of electron microscopy and atomic force microscopy techniques. Selected examples are highlighted showing data obtained using these techniques, which provide a powerful suite of methods to probe ordering from the molecular scale to the aggregate superstructure.

Recent advances in self-assembled peptides: Implications for targeted drug delivery and vaccine engineering

Self-assembled peptides have shown outstanding characteristics for vaccine delivery and drug targeting. Peptide molecules can be rationally designed to self-assemble into specific nanoarchitectures in response to changes in their assembly environment including: pH, temperature, ionic strength, and interactions between host (drug) and guest molecules. The resulting supramolecular nanostructures include nanovesicles, nanofibers, nanotubes, nanoribbons, and hydrogels and have a diverse range of mechanical and physicochemical properties. These molecules can be designed for cell-specific targeting by including adhesion ligands, receptor recognition ligands, or peptide-based antigens in their design, often in a multivalent display. Depending on their design, self-assembled peptide nanostructures have advantages in biocompatibility, stability against enzymatic degradation, encapsulation of hydrophobic drugs, sustained drug release, shear-thinning viscoelastic properties, and/or adjuvanting properties. These molecules can also act as intracellular transporters and respond to changes in the physiological environment. Furthermore, this class of materials has shown sequence- and structure-dependent impacts on the immune system that can be tailored to non-immunogenic for drug targeting, and immunogenic for vaccine delivery. This review explores self-assembled peptide nanostructures (beta sheets, alpha helices, peptide amphiphiles, amino acid pairing, elastin like polypeptides, cyclic peptides, short peptides, Fmoc peptides, and peptide hydrogels) and their application in vaccine delivery and drug targeting.

Hybrid membrane biomaterials from self-assembly in polysaccharide and peptide amphiphile mixtures: controllable structural and mechanical properties and antimicrobial activity

Macroscopic capsules, with tunable properties based on hierarchical self-assembly on multiple lengthscales, are prepared from the co-operative self-assembly of polysaccharide and peptide amphiphiles.

Structural behaviour and gene delivery in complexes formed between DNA and arginine-containing peptide amphiphiles

We describe in depth the structure of complexes formed between DNA and two classes of arginine-containing peptide amphiphiles, namely, the lipopeptide PRW-C₁₆ (P = proline, R = arginine, W = tryptophan, C₁₆ = C16 : 0 alkyl chain) and the bolaamphiphile RFL₄FR (R = arginine, F = phenylalanine, L = leucine). A combination of X-ray and neutron scattering provided unprecedented insights into the local structure of these complexes. Lipopeptide-based complexes self-assembled into layered structures with large-scale fractal features, hosting DNA in the interstices. Bola-amphiphile scaffolds were characterized by planar structures with DNA strands presumably sandwiched in-between peptide nanotapes. Importantly, complexation did not affect the structural integrity of DNA in either of the two complexes. The bolaamphiphile conjugates displayed high levels of molecular ordering in contrast to the liquid-crystalline features observed in lipopeptide assemblies. Peptide-DNA complexes were assessed for their potential as a means to deliver the reporter vector pEGFP-N1 into SW480 human colon carcinoma cells. Successfully transfected cells expressed green fluorescent protein. The potentiating effect of PRW-C₁₆ on the cellular uptake of ectopic DNA was found to be much greater than that observed with RFL₄FR. In contrast to the bolaamphiphile-based conjugate, the liquid-crystalline nature of the lipopeptide complex is likely to play a key role in DNA release and transfection efficiency since these weakly bound structures require lower energy expenditure during disassembly and load release.

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.

Rational design of fiber forming supramolecular structures

Recent strides in the development of multifunctional synthetic biomimetic materials through the self-assembly of multi-domain peptides and proteins over the past decade have been realized. Such engineered systems have wide-ranging application in bioengineering and medicine. This review focuses on fundamental fiber forming α-helical coiled-coil peptides, peptide amphiphiles, and amyloid-based self-assembling peptides; followed by higher order collagen- and elastin-mimetic peptides with an emphasis on chemical / biological characterization and biomimicry.

Catanionic drug-derivative nano-objects constructed by chlorambucil and its derivative for efficient leukaemia therapy

A new carrier-free catanionic drug-derivative nano-object strategy is developed for leukaemia therapy. The as-prepared drug-derivative nano-objects are formed by ionic pairs of hydrophobic anticancer drug chlorambucil (CLB) and its derivative N-(2-Amino-ethyl)-4-{4-[bis-(2-chloro-ethyl)-amino]-phenyl}-butyramide (CLBM). The designed drug delivery system has the advantage of 100% drug content without additional carrier materials. The ionic pairs are formed by proton exchange between CLB and CLBM. Due to the amphiphilicity of the ionic pairs, they can assemble into well-defined drug-derivative (CLB-CLBM) nano-objects. Series of techniques such as transmission electron microscopy (TEM), dynamic light scattering (DLS) and electrical conductivity are used to investigate the property of the solution and aggregation behaviour of as-prepared drug-derivative ionic pairs. In vitro drug release study of the as-prepared nano-objects shows their prolonged drug release behavior. Specifically, in vitro cytotoxicity results of these nano-objects show obviously higher cytotoxicity, which is promising for clinical efficacy. This study may pave the way for the fabrication of carrier-free drug delivery system with efficient cancer therapy.

Programming Bioactive Architectures with Cyclic Peptide Amphiphiles

We present a versatile approach for the synthesis of cyclic peptide amphiphiles of the hormone somatostatin (SST) with tunable lipophilic tails to program bioactive nanoarchitectures. A novel bis-alkylation reagent is synthesized that facilitates the functionalization of SST with a thiol anchor. Different hydrophobic moieties are introduced inspired by a biomimetic palmitoylation approach which opens access to cyclic peptide amphiphiles that display rich self-organization and cell membrane interactions.

Toll-like receptor agonist lipopeptides self-assemble into distinct nanostructures

The self-assembled structure of toll-like receptor agonist lipopeptides containing the CSK4 peptide sequence is examined in aqueous solution. A remarkable dependence of morphology on the number of attached hexadecyl lipid chains is demonstrated, with spherical micelle structures for mono- and di-lipidated structures observed, but flexible wormlike micelles for the homologue containing three lipid chains. The distinct modes of assembly may have an important influence on the bioactivity of this class of lipopeptide.

New self-assembling multifunctional templates for the biofabrication and controlled self-release of cultured tissue

The need to source live human tissues for research and clinical applications has been a major driving force for the development of new biomaterials. Ideally, these should elicit the formation of scaffold-free tissues with native-like structure and composition. In this study, we describe a biologically interactive coating that combines the fabrication and subsequent self-release of live purposeful tissues using template-cell-environment feedback. This smart coating was formed from a self-assembling peptide amphiphile comprising a protease-cleavable sequence contiguous with a cell attachment and signaling motif. This multifunctional material was subsequently used not only to instruct human corneal or skin fibroblasts to adhere and deposit discreet multiple layers of native extracellular matrix but also to govern their own self-directed release from the template solely through the action of endogenous metalloproteases. Tissues recovered through this physiologically relevant process were carrier-free and structurally and phenotypically equivalent to their natural counterparts. This technology contributes to a new paradigm in regenerative medicine, whereby materials are able to actively direct and respond to cell behavior. The novel application of such materials as a coating capable of directing the formation and detachment of complex tissues solely under physiological conditions can have broad use for fundamental research and in future cell and tissue therapies.

Self-assembly of a dual functional bioactive peptide amphiphile incorporating both matrix metalloprotease substrate and cell adhesion motifs

We describe a bioactive lipopeptide that combines the capacity to promote the adhesion and subsequent self-detachment of live cells, using template-cell-environment feedback interactions. This self-assembling peptide amphiphile comprises a diene-containing hexadecyl lipid chain (C16e) linked to a matrix metalloprotease-cleavable sequence, Thr-Pro-Gly-Pro-Gln-Gly-Ile-Ala-Gly-Gln, and contiguous with a cell-attachment and signalling motif, Arg-Gly-Asp-Ser. Biophysical characterisation revealed that the PA self-assembles into 3 nm diameter spherical micelles above a critical aggregation concentration (cac). In addition, when used in solution at 5-150 nM (well below the cac), the PA is capable of forming film coatings that provide a stable surface for human corneal fibroblasts to attach and grow. Furthermore, these coatings were demonstrated to be sensitive to metalloproteases expressed endogenously by the attached cells, and consequently to elicit the controlled detachment of cells without compromising their viability. As such, this material constitutes a novel class of multi-functional coating for both fundamental and clinical applications in tissue engineering.

Self-Assembly of a Designed Alternating Arginine/Phenylalanine Oligopeptide

A model octapeptide peptide consisting of an alternating sequence of arginine (Arg) and phenylalanine (Phe) residues, namely, [Arg-Phe]4, was prepared, and its self-assembly in solution studied. The simple alternating [Arg-Phe]4 peptide sequence allows for unique insights into the aggregation process and the structure of the self-assembled motifs. Fluorescence and UV-vis assays were used to determine critical aggregation concentrations, corresponding to the formation of oligomeric species and β-sheet rich structures organized into both spheroidal aggregates and highly ordered fibrils. Electron and atomic force microscopy images show globular aggregates and long unbranched fibers with diameters ranging from ∼4 nm up to ∼40 nm. Infrared and circular dichroism spectroscopy show the formation of β-sheet structures. X-ray diffraction on oriented stalks show that the peptide fibers have an internal lamellar structure, with an orthorhombic unit cell with parameters a ∼ 27.6 Å, b ∼ 9.7 Å, and c ∼ 9.6 Å. In situ small-angle X-ray scattering (SAXS) shows the presence of low molecular weight oligomers in equilibrium with mature fibers which are likely made up from 5 or 6 intertwined protofilaments. Finally, weak gel solutions are probed under gentle shear, suggesting the ability of these arginine-rich fibers to form networks.

Multiwalled nanotubes formed by catanionic mixtures of drug amphiphiles

Mixing of oppositely charged amphiphilic molecules (catanionic mixing) offers an attractive strategy to produce morphologies different from those formed by individual molecules. We report here on the use of catanionic mixing of anticancer drug amphiphiles to construct multiwalled nanotubes containing a fixed and high drug loading. We found that the molecular mixing ratio, the solvent composition, the overall drug concentrations, as well as the molecular design of the studied amphiphiles are all important experimental parameters contributing to the tubular morphology. We believe these results demonstrate the remarkable potential that anticancer drugs could offer to self-assemble into discrete nanostructures and also provide important insight into the formation mechanism of nanotubes by catanionic mixtures. Our preliminary animal studies reveal that the CPT nanotubes show significantly prolonged retention time in the tumor site after intratumoral injection.

Self-assembling amphiphilic peptides

The self-assembly of several classes of amphiphilic peptides is reviewed, and selected applications are discussed. We discuss recent work on the self-assembly of lipopeptides, surfactant-like peptides and amyloid peptides derived from the amyloid-β peptide. The influence of environmental variables such as pH and temperature on aggregate nanostructure is discussed. Enzyme-induced remodelling due to peptide cleavage and nanostructure control through photocleavage or photo-cross-linking are also considered. Lastly, selected applications of amphiphilic peptides in biomedicine and materials science are outlined.

Self-assembly of peptides to nanostructures

The formation of well-ordered nanostructures through self-assembly of diverse organic and inorganic building blocks has drawn much attention owing to their potential applications in biology and chemistry. Among all organic building blocks, peptides are one of the most promising platforms due to their biocompatibility, chemical diversity, and resemblance to proteins. Inspired by the protein assembly in biological systems, various self-assembled peptide structures have been constructed using several amino acids and sequences. This review focuses on this emerging area, the recent advances in peptide self-assembly, and formation of different nanostructures, such as tubular structures, fibers, vesicles, and spherical and rod-coil structures. While different peptide nanostructures have been discovered, potential applications are explored in drug delivery, tissue engineering, wound healing, and surfactants.

Silica templating of a self-assembling peptide amphiphile that forms nanotapes

The peptide amphiphile C16-KTTKS templates silica polymerization, enabling the production of silica nanotape structures, imaged via electron microscopy (TEM and SEM). X-ray scattering shows that the nanotapes comprise stacked layers, as for the parent peptide amphiphile, but with a substantially increased layer spacing resulting from silica polymerization.

Co-assembly of aromatic dipeptides into spherical structures that are similar in morphology to red and white blood cells

This paper describes the co-assembly of two aromatic dipeptides, diphenylalanine and Fmoc-l-DOPA(acetonated)-d-Phe-OMe, into different spherical structures that are similar in morphology to either red or white blood cells. Under the examined experimental conditions, each of the peptides formed spherical nanostructures, but a mixture of the two peptides generated new types of assemblies. When the concentration of the two peptides was 1 mg mL^-1 they self-assembled into oval biconcave disk nanostructures that are similar in morphology to red blood cells. When the concentration of the peptides was higher they formed spherical structures with bulges on their outer surface. These assemblies are similar in morphology to white blood cells. We determined the morphology and structure of the assemblies using atomic force microscopy and electron microscopy and their secondary structure using ATR-FTIR and CD. In addition, we studied the co-assembly of Fmoc-DOPA(acetonated)-d-Phe-OMe with other diphenylalanine analogues. Furthermore, we showed that the red blood cell-like structures can adsorb and release the anticancer drug, doxorubicin, and therefore might be useful as a system for sustained drug release.

Co-assembly of tetrapeptides into complex pH-responsive molecular hydrogel networks

Here we prepare pH-responsive complex molecular hydrogels from oppositely charged tetrapeptidic components that can be pH-tuned resulting in interconversion between different networks.