Micellization of Lipopeptides Containing Toll-like Receptor Agonist and Integrin Binding Sequences

Short bioactive peptide sequences are of great interest in biomaterials development. We investigate the self-assembly of a lipopeptide containing both the highly cationic CSK4 toll-like receptor agonist hexapeptide sequence and RGDS integrin-binding motif, i.e., C16-CSK4RGDS, as well as the control containing a scrambled terminal sequence C16-CSK4GRDS. Both lipopeptides are found to form micelles, as revealed by small-angle X-ray scattering and cryogenic transmission electron microscopy, and modeled using atomistic molecular dynamics simulations. We carefully examined methods to probe the aggregation of the molecules, i.e. to obtain the critical micelle concentration (CMC). Fluorescent probe assays using 1-anilino-8-naphthalenesulfonate (ANS) reveal low CMC values, 1-2 μM, which contrast with consistent values more than 2 orders of magnitude larger obtained from surface tension and electrical conductivity as well as unexpected UV/vis absorption spectra discontinuities and fluoresccence probe assays using Nile red. The anomalous results obtained from an ANS fluorescence probe are ascribed to the effect of ANS binding to the cationic (lysine and arginine) residues in the lipopeptide, which leads to a conformational change, as shown by circular dichroism, even at low concentrations below the actual CMC. Despite the small change in the peptide sequence (swapping of G and R residues), there is surprisingly a significant difference in the aggregation propensity and association number, both of which are greater for C16-CSK4GRDS. Both lipopeptides are cytocompatible (with fibroblasts and myoblasts) at low concentration, although cytotoxicity is noted at higher concentration.

Size and Polarizability of Boron Cluster Carriers Modulate Chaotropic Membrane Transport

Perhalogenated closo-borates represent a new class of membrane carriers. They owe this activity to their chaotropicity, which enables the transport of hydrophilic molecules across model membranes and into living cells. The transport efficiency of this new class of cluster carriers depends on a careful balance between their affinity to membranes and cargo, which varies with chaotropicity. However, the structure-activity parameters that define chaotropic transport remain to be elucidated. Here, we have studied the modulation of chaotropic transport by decoupling the halogen composition from the boron core size. The binding affinity between perhalogenated decaborate and dodecaborate clusters carriers was quantified with different hydrophilic model cargos, namely a neutral and a cationic peptide, phalloidin and (KLAKLAK)2. The transport efficiency, membrane-lytic properties, and cellular toxicity, as obtained from different vesicle and cell assays, increased with the size and polarizability of the clusters. These results validate the chaotropic effect as the driving force behind the membrane transport propensity of boron clusters. This work advances our understanding of the structural features of boron cluster carriers and establishes the first set of rational design principles for chaotropic membrane transporters.

Chirality Supramolecular Systems: Helical Assemblies, Structure Designs, and Functions

Chirality, as one of the most striking characteristics, exists at various scales in nature. Originating from the interactions of host and guest molecules, supramolecular chirality possesses huge potential in the design of functional materials. Here, an overview of the recent progress in structure designs and functions of chiral supramolecular materials is present. First, three design routes of the chiral supramolecular structure are summarized. Compared with the template-induced and chemical synthesis strategies that depend on accurate molecular identification, the twisted-assembly technique creates chiral materials through the ordered stacking of the nanowire or films. Next, chirality inversion and amplification are reviewed to explain the chirality transfer from the molecular level to the macroscopic scale, where the available external stimuli on the chirality inversion are also given. Lastly, owing to the optical activity and the characteristics of the layer-by-layer stacking structure, the supramolecular chirality materials display various excellent performances, including smart response, shape-memorization, superior mechanical performance, and applications in biomedical fields. To sum up, this work provides a systematic review of the helical assemblies, structure design, and applications of supramolecular chirality systems.

Lipopeptides as tools in catalysis, supramolecular, materials and medicinal chemistry

Lipopeptides are amphiphilic peptides in which an aliphatic chain is attached to either the C or N terminus of peptides. Their self-assembly - into micelles, vesicles, nanotubes, fibres or nanobelts - leads to applications in nanotechnology, catalysis or medicinal chemistry. Self-organization of lipopeptides is dependent on both the length of the lipid tail and the amino acid sequence, in which the chirality of the peptide sequence can be transmitted into the supramolecular species. This Review describes the use of lipopeptides to design synthetic advanced dynamic supramolecular systems, nanostructured materials or self-responsive delivery systems in the area of medical biotechnology. We examine the influence of external stimuli, the ability of lipopeptide-derived structures to adapt over time and their application as medicinal agents with antibacterial, antifungal, antiviral or anticancer activities. Finally, we discuss the catalytic efficiency of lipopeptides, with the aim of building minimal synthetic enzymes, and recent efforts to incorporate metals into lipopeptide assemblies.

Dynamic exchange controls the assembly structure of nucleic-acid-peptide chimeras

Recent attempts to develop the next generation of functional biomaterials focus on systems chemistry approaches exploiting dynamic networks of hybrid molecules. This task is often found challenging, but we herein present ways for profiting from the multiple interaction interfaces forming Nucleic-acid-Peptide assemblies and tuning their formation. We demonstrate that the formation of well-defined structures by double-stranded DNA-peptide conjugates (dsCon) is restricted to a specific range of environmental conditions and that precise DNA hybridization, satisfying the interaction interfaces, is a crucial factor in this process. We further reveal the impact of external stimuli, such as competing free DNA elements or salt additives, which initiate dynamic interconversions, resulting in hybrid structures exhibiting spherical and fibrillar domains or a mixture of spherical and fibrillar particles. This extensive analysis of the co-assembly systems chemistry offers new insights into prebiotic hybrid assemblies that may now facilitate the design of new functional materials. We discuss the implications of these findings for the emergence of function in synthetic materials and during early chemical evolution.

Self-Assembly of the Tetraphenylethylene-Capped Diserine through a Hierarchical Assembly Process

We report a new peptide-based urchin-shaped structure prepared through two-step self-assembly of tetraphenylethylene-diserine (TPE-SS). Hydrogelation generated nanobelts through the first stage of self-assembly of TPE-SS; these nanobelts further transformed on silicon wafers into urchin-like microstructures featuring nanosized spines. The presence of the TPE moiety in the hydrogelator resulted in aggregation-induced emission characteristics both in the solution and in the gel phases. TPE-SS has the lowest molecular weight of any TPE-capped hydrogelator with β-sheet-like structures under physiological pH. This new design strategy appears to be useful for generating three-dimensional self-assembled microstructures and multifunctional biomaterials. We found that TPE-SS is biocompatible with human mesenchymal stem cells and breast cancer cells, making them potential applications in tissue engineering and biomedical research.

Translational aspect in peptide drug discovery and development: An emerging therapeutic candidate

In the last two decades, protein-protein interactions (PPIs) have been used as the main target for drug development. However, with larger or superficial binding sites, it has been extremely difficult to disrupt PPIs with small molecules. On the other hand, intracellular PPIs cannot be targeted by antibodies that cannot penetrate the cell membrane. Peptides that have a combination of conformational rigidity and flexibility can be used to target difficult binding interfaces with appropriate binding affinity and specificity. Since the introduction of insulin nearly a century ago, more than 80 peptide drugs have been approved to treat a variety of diseases. These include deadly diseases such as cancer and human immunodeficiency virus infection. It is also useful against diabetes, chronic pain, and osteoporosis. Today, more research is being done on these drugs as lessons learned from earlier approaches, which are still valid today, complement newer approaches such as peptide display libraries. At the same time, integrated genomics and peptide display libraries are new strategies that open new avenues for peptide drug discovery. The purpose of this review is to examine the problems in elucidating the peptide-protein recognition mechanism. This is important to develop peptide-based interventions that interfere with endogenous protein interactions. New approaches are being developed to improve the binding affinity and specificity of existing approaches and to develop peptide agents as potentially useful drugs. We also highlight the key challenges that must be overcome in peptide drug development to realize their potential and provide an overview of recent trends in peptide drug development. In addition, we take an in-depth look at early efforts in human hormone discovery, smart medicinal chemistry and design, natural peptide drugs, and breakthrough advances in molecular biology and peptide chemistry.

The self-assembled zein hydrolysate-curcumin nanocomplex: improvement on the stability and sustainable release of curcumin

BACKGROUND

The bioavailability of curcumin (Cur) is generally limited by its poor stability. However, it is beneficial to improve the stability of Cur by using self-assembled zein hydrolysate (ZH) as delivery carrier. This paper aimed to explore the formation mechanism of zein hydrolysate-curcumin nanocomplexes as a function of critical micelle concentration (CMC).

RESULTS

In this work, The CMC of ZH (0.535 mg mL^-1 ) was obtained by the pyrene fluorescent probe method. ZH-Cur nanocomplexes undergo hydrogen bonding and hydrophobic interactions, and the fluorescence quenching effect was concentration dependent with the process of static quenching. Moreover, the differences of colloidal properties on ZH and ZH-Cur nanocomplexes were systematically compared by dynamic light scattering and scanning electron microscopy near CMC. ZH presented irregular spherical shapes and would aggregate to form micelles at the CMC and above. The tight micellar structure promoted more uniform size distribution (double peaks reduced) and higher potentials (over -30 mV) within 10 days. In addition, the nanocomplexes demonstrated an obvious core-shell structure. Within 10 days of storage, the particle size distributions were uniform and the potentials increased significantly, indicating that the micellar nanostructure made the Cur stably embedded in the hydrophobic core of ZH. Finally, ZH-Cur nanocomplexes effectively improved the water solubility and encapsulation rate (over 70%) of Cur. Moreover, over 90% of Cur was released steadily within 91 h.

CONCLUSION

This work provided a theoretical basis for the application of amphiphilic peptide micellar nanostructure as novel food-grade nanocarriers to transport hydrophobic bioactive substances. © 2022 Society of Chemical Industry.

FEK self-assembled peptide hydrogels facilitate primary hepatocytes culture and pharmacokinetics screening

A FEFEFKFK (FEK, F, phenylalaninyl; E, glutamyl; K, lysinyl)-based self-assembling peptide hydrogel (FEK-SAPH) was developed to replace sandwich culture (SC) for improved culture of primary hepatocytes in vitro. Under neutral conditions, FEK self-assembles to form β-sheet nanofibers, which in turn form FEK-SAPH. For the culture of rat primary hepatocytes (RPH), the use of FEK-SAPH simplified operation steps and promoted excellent cell-cell interactions while maintaining the SC-related RPH polarity trend. Compared with SC, FEK-SAPH cultured RPH for 14 days, the bile duct network was formed, the secretion of albumin and urea was improved, and the metabolic clearance rate based on cytochrome P450 (CYPs) was comparable. In FEK-SAPH culture, the expression level of the biliary efflux transporter bile salt export pump increased by 230.7%, while the biliary excretion index value of deuterium-labeled sodium taurocholate (d8-TCA) differed slightly from the SC value (72% and 77%, respectively, p = .0195). The inhibitory effect of cholestasis drugs on FEK-SAPH was significantly higher than that of SC. In FEK-SAPH, hepatoprotective drugs were more effective in antagonizing hepatotoxicity induced by lithocholic acid (LCA). FEK-SAPH cultured RPH with hepatoprotective drugs can better recover from LCA-induced damage. In summary, FEK-SAPH can be used as a substitute for SC for pharmacokinetic screening to evaluate the drug absorption, disposition, metabolism, excretion, and toxicity (ADMET) in hepatocytes.

Organic/inorganic hydrogels by simultaneous self-assembly and mineralization of aromatic short-peptides

Hybrid hydrogels with a tunable structure–function relationship were prepared by simultaneous self-assembly and mineralization of aromatic short-peptides. Sub-stoichiometric Ca concentrations resulted in nanoapatite oriented along the peptide fiber.

In silico-screened cationic dipeptides from scallop with synergistic gelation effect on ι-carrageenan

In this paper, some cationic dipeptides from scallop (Patinopecten yessoensis) male gonads (SMGs), which can synergistically gel with ι-carrageenan (ι-C), were screened by the in silico approach. Fourteen protein sequences of SMGs were obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and nano liquid chromatography-mass spectrometry/mass spectrometry (nanoLC-MS/MS) analysis and were then hydrolyzed via in silico simulation. A total of 414 sequences were obtained with 56 duplicates, half of which were positively charged at pH 7. Among the cation sequences, 171 had good water solubility, including two amino acids (Lys and Arg). The molecular weight analysis of the cationic water-soluble sequences showed that 0.2-0.3 kDa accounted for the highest proportion. Based on the obvious synergistic effect of Lys and ι-C, 11 Lys-containing dipeptides, including Ser-Lys (SK), Thr-Lys (TK), Trp-Lys (WK), Ala-Lys (AK), Leu-Lys (LK), Gly-Lys (GK), Val-Lys (VK), Cys-Lys (CK), Asn-Lys (NK), Phe-Lys (FK), and Met-Lys (MK), were finally screened out to study gelation with ι-C. It was found that the dipeptides/ι-C formed firm gels except WK/ι-C. The values of the storage modulus (G') of 11 dipeptides/ι-C were investigated by a rheometer. The G' of 8 dipeptides/ι-C was higher than 1000 Pa. These results indicated that the in silico-screened dipeptides from SMGs can form composite gels with ι-C, which can be used for the design and development of functional hydrogels.

Revealing the dynamic adsorption and diffusion of peptide amphiphile on supported lipid bilayer by single molecule experiment and simulation

Dynamic adsorption and diffusion of peptide amphiphiles (PAs) with different numbers of alkyl tails on supported lipid bilayers (SLBs) were investigated by single molecule tracking experiment and molecule dynamic simulation. Experimental results show two distinct populations of PAs with different residence time. Residence time of adsorbed PAs increases with the increase of the alkyl tails, whereas diffusion coefficient monotonically decreases with rising the number of alkyl tails and also decreases with increasing the mobility of SLBs. All-atom molecule dynamic simulation results prove that the adsorption and diffusion of PAs on SLB surface are mainly determined by interactions between PAs and SLBs and also the intrinsic mobility of PAs in aqueous solution. The electrostatic interactions and the mobility of PAs are two dominated but contradictory coefficients for the adsorption and diffusion of PAs. By increasing the alkyl tails, the mobility of PAs decreases while the electrostatic property does not change significantly, resulting in the increase of residence time and decrease of diffusivity of PAs. Additionally, for the PAs with large number of alkyl tails (≥ 3 alkyl tails), steric hindrance of alkyl tails leads to the decrease of adsorption probability of PAs on SLB surface. These findings lay the groundwork for guiding the design of PAs with high cell affinity, potentially useful for efficient drug delivery.

Gel properties and network structure of the hydrogel constructed by iota-carrageenan and Ala-Lys dipeptide

Gel properties of hydrogel-forming by Ala-Lys dipeptide (AK) and iota-carrageenan (ι-C) were investigated by rheological behavior, fourier transform infrared analysis, cryo-scanning electron microscopy, low field-NMR relaxometry and magnetic resonance imaging. Iota-carrageenan was changed from a liquid to a gel with the addition of AK, and the existence of AK significantly increased the storage modulus (G') of ι-C from 590.4 to 1077.8 Pa. In the ι-C/AK gel, the blue-shift of OH stretching and water deformation were observed, meanwhile, the presence of amide I band at 1682 cm^-1 was observed. The network of ι-C/AK gel showed a dense honeycomb structure with flocculating continuous phase and rough entanglement morphology. After adding AK, the water free in the pores of ι-C entered the ι-C/AK gel matrix, and the binding capacity of bound water was enhanced. These scenarios proved that the AK as the cationic dipeptide could control the conversion of negatively charged ι-C from an original random structure to a helical structure due to electrostatic interactions and hydrogen bonds. This study provides a new opportunity for the peptides into carbohydrate-based gel matrices, which could provide insights for the further application of ι-C/AK gels in the fields of food industry, tissue engineering and drug delivery.

Bioactive potential of natural biomaterials: identification, retention and assessment of biological properties

Biomaterials have had an increasingly important role in recent decades, in biomedical device design and the development of tissue engineering solutions for cell delivery, drug delivery, device integration, tissue replacement, and more. There is an increasing trend in tissue engineering to use natural substrates, such as macromolecules native to plants and animals to improve the biocompatibility and biodegradability of delivered materials. At the same time, these materials have favourable mechanical properties and often considered to be biologically inert. More importantly, these macromolecules possess innate functions and properties due to their unique chemical composition and structure, which increase their bioactivity and therapeutic potential in a wide range of applications. While much focus has been on integrating these materials into these devices via a spectrum of cross-linking mechanisms, little attention is drawn to residual bioactivity that is often hampered during isolation, purification, and production processes. Herein, we discuss methods of initial material characterisation to determine innate bioactivity, means of material processing including cross-linking, decellularisation, and purification techniques and finally, a biological assessment of retained bioactivity of a final product. This review aims to address considerations for biomaterials design from natural polymers, through the optimisation and preservation of bioactive components that maximise the inherent bioactive potency of the substrate to promote tissue regeneration.

Amyloid-Like Aggregation in Diseases and Biomaterials: Osmosis of Structural Information

The discovery that the polypeptide chain has a remarkable and intrinsic propensity to form amyloid-like aggregates endowed with an extraordinary stability is one of the most relevant breakthroughs of the last decades in both protein/peptide chemistry and structural biology. This observation has fundamental implications, as the formation of these assemblies is systematically associated with the insurgence of severe neurodegenerative diseases. Although the ability of proteins to form aggregates rich in cross-β structure has been highlighted by recent studies of structural biology, the determination of the underlying atomic models has required immense efforts and inventiveness. Interestingly, the progressive molecular and structural characterization of these assemblies has opened new perspectives in apparently unrelated fields. Indeed, the self-assembling through the cross-β structure has been exploited to generate innovative biomaterials endowed with promising mechanical and spectroscopic properties. Therefore, this structural motif has become the fil rouge connecting these diversified research areas. In the present review, we report a chronological recapitulation, also performing a survey of the structural content of the Protein Data Bank, of the milestones achieved over the years in the characterization of cross-β assemblies involved in the insurgence of neurodegenerative diseases. A particular emphasis is given to the very recent successful elucidation of amyloid-like aggregates characterized by remarkable molecular and structural complexities. We also review the state of the art of the structural characterization of cross-β based biomaterials by highlighting the benefits of the osmosis of information between these two research areas. Finally, we underline the new promising perspectives that recent successful characterizations of disease-related amyloid-like assemblies can open in the biomaterial field.

The structural reconformation of peptides in enhancing functional and therapeutic properties: Insights into their solid state crystallizations

Therapeutic peptides derived proteins with alpha-reconformation states like antibody shape have shown potential effects in combating terrible diseases linked with earlier signs of angiogensis, mutagenesis and transgenesis. Alpha reconformation in material design refers to the folding of the peptide chains and their transitions under reversible chemical bonds of disulfide chemical bridges and further non-covalence lesions. Thus, the rational design of signal peptides into alpha-helix is intended in increasing the defending effects of peptides into cores like adjuvant antibiotic and/or vaccines. Thereby, the signal peptides are able in displaying multiple eradicating regions by changing crystal-depositions and deviation angles. These types of molecular structures could have multiple advantages in tracing disease syndromes and impurities by increasing the host defense against the fates of pathogens and viruses, eventually leading to the loss in signaling by increasing peptide susceptibility levels to folding and unfolding and therefore, formation of transgenic peptide models. Alpha reconformation peptides is aimed in triggering as well as other regulatory functions such as remodulating metabolic chain disorders of lipolysis and glucolysis by increasing the insulin and leptin resistance for best lipid storages and lipoprotein density distributions.

Diffusion behavior of peptide amphiphiles containing different numbers of alkyl tails at a hydrophobic solid-liquid interface: single molecule tracking investigation

Using the single molecule tracking technique, the diffusion behavior of peptide amphiphiles (PAs) with different numbers of alkyl tails at a hydrophobic solid-liquid interface has been investigated. The effect of the number of alkyl tails of PAs on molecular trajectories at the hydrophobic solid-liquid interface has been systematically studied. PA molecules display an intermittent motion consisting of immobilization and hopping processes, which has been well simulated by the continuous time random walk (CTRW) model. The results reveal that the hydrophobic interaction between the PAs and hydrophobic surface plays an important role in the diffusion behavior of PAs. Increasing the number of alkyl tails in PAs systematically reduces the mobility of PAs on the hydrophobic surface. Moreover, the diffusion behavior of PAs at the hydrophobic interface also shows pH dependence. A decrease in pH is beneficial to the motion of all PAs on the hydrophobic surface, which can be ascribed to the protonation of PAs in acidic solutions. Therefore, the hydrophobic interaction is crucial to the transport of peptide amphiphiles at hydrophobic interfaces which would be important for the design of peptides in biological applications.

Investigation of α/γ hybrid peptide self-assembled structures with antimicrobial and antibiofilm properties

The present work describes the synthesis and characterization of α/γ hybrid peptides, Boc-Phe-γ⁴ -Phe-Val-OMe, P1; Boc-Ala-γ⁴ -Phe-Val-OMe, P2; and Boc-Leu-γ⁴ -Phe-Val-OMe, P3 together with the formation of self-assembled structures formed by these hybrid peptides in dimethyl sulfoxide (DMSO)/water (1:1). The self-assembled structures were characterized by infrared (IR) spectroscopy, circular dichroism (CD), and scanning electron microscopy (SEM). Further, α/γ hybrid peptide self-assembled structures were evaluated for antibacterial properties. Among all, the self-assembled peptide P1 exhibited the antimicrobial activity against Escherichia coli and Klebsiella pneumoniae, while self-assembled peptide P3 inhibited the biofilms of Salmonella typhimurium and Pseudomonas aeruginosa. In this study, we have shown the significance of self-assembled structures formed from completely hydrophobic α/γ hybrid peptides in exploring the antibacterial properties together with biofilm inhibition.

Peptide-TLR-7/8a conjugate vaccines chemically programmed for nanoparticle self-assembly enhance CD8 T-cell immunity to tumor antigens

Personalized cancer vaccines targeting patient-specific neoantigens are a promising cancer treatment modality; however, neoantigen physicochemical variability can present challenges to manufacturing personalized cancer vaccines in an optimal format for inducing anticancer T cells. Here, we developed a vaccine platform (SNP-7/8a) based on charge-modified peptide-TLR-7/8a conjugates that are chemically programmed to self-assemble into nanoparticles of uniform size (~20 nm) irrespective of the peptide antigen composition. This approach provided precise loading of diverse peptide neoantigens linked to TLR-7/8a (adjuvant) in nanoparticles, which increased uptake by and activation of antigen-presenting cells that promote T-cell immunity. Vaccination of mice with SNP-7/8a using predicted neoantigens (n = 179) from three tumor models induced CD8 T cells against ~50% of neoantigens with high predicted MHC-I binding affinity and led to enhanced tumor clearance. SNP-7/8a delivering in silico-designed mock neoantigens also induced CD8 T cells in nonhuman primates. Altogether, SNP-7/8a is a generalizable approach for codelivering peptide antigens and adjuvants in nanoparticles for inducing anticancer T-cell immunity.

Directive Effect of Chain Length in Modulating Peptide Nano-assemblies

BACKGROUND

RADA-4 (Ac-RADARADARADARADA-NH2) is the most extensively studied and marketed self-assembling peptide, forming hydrogel, used to create defined threedimensional microenvironments for cell culture applications.

OBJECTIVES

In this work, we use various biophysical techniques to investigate the length dependency of RADA aggregation and assembly.

METHODS

We synthesized a series of RADA-N peptides, N ranging from 1 to 4, resulting in four peptides having 4, 8, 12, and 16 amino acids in their sequence. Through a combination of various biophysical methods including thioflavin T fluorescence assay, static right angle light scattering assay, Dynamic Light Scattering (DLS), electron microscopy, CD, and IR spectroscopy, we have examined the role of chain-length on the self-assembly of RADA peptide.

RESULTS

Our observations show that the aggregation of ionic, charge-complementary RADA motifcontaining peptides is length-dependent, with N less than 3 are not forming spontaneous selfassemblies.

CONCLUSION

The six biophysical experiments discussed in this paper validate the significance of chain-length on the epitaxial growth of RADA peptide self-assembly.

Linker-Regulated H2S Release from Aromatic Peptide Amphiphile Hydrogels

Controlled release is an essential requirement for delivery of hydrogen sulfide (H₂S) because of its reactive nature, short half-life in biological fluids, and toxicity at high concentrations. In this context, H₂S delivery via hydrogels may be beneficial as they can deliver H₂S locally at the site of interest. Herein, we employed hydrogels based on aromatic peptide amphiphiles (APAs) with tunable mechanical properties to modulate the rates of H₂S release. The APAs contained an aromatic S-aroylthiooxime (SATO) H₂S donor attached with a linker to a short IAVEEE hexapeptide. Linker units included carbonyl, substituted O-methylenes, alkenyl, and alkyl segments with the goal of evaluating the role of linker structure on self-assembly, capacity for hydrogelation, and H₂S release rate. We studied each peptide by transmission electron microscopy, circular dichroism spectroscopy, and rheology, and we measured H₂S release rates from each gel, triggering SATO decomposition and release of H₂S by addition of cysteine (Cys). Using an H₂S-selective electrode probe as well as a turn-on fluorescent H₂S probe in the presence of H9C2 cardiomyocytes, we found that the rate of H₂S release from the hydrogels depended on the rate of Cys penetration into the nanofiber core with stiffer gels showing longer overall release.

Soft-Matter Nanotubes: A Platform for Diverse Functions and Applications

Self-assembled organic nanotubes made of single or multiple molecular components can be classified into soft-matter nanotubes (SMNTs) by contrast with hard-matter nanotubes, such as carbon and other inorganic nanotubes. To date, diverse self-assembly processes and elaborate template procedures using rationally designed organic molecules have produced suitable tubular architectures with definite dimensions, structural complexity, and hierarchy for expected functions and applications. Herein, we comprehensively discuss every functions and possible applications of a wide range of SMNTs as bulk materials or single components. This Review highlights valuable contributions mainly in the past decade. Fifteen different families of SMNTs are discussed from the viewpoints of chemical, physical, biological, and medical applications, as well as action fields (e.g., interior, wall, exterior, whole structure, and ensemble of nanotubes). Chemical applications of the SMNTs are associated with encapsulating materials and sensors. SMNTs also behave, while sometimes undergoing morphological transformation, as a catalyst, template, liquid crystal, hydro-/organogel, superhydrophobic surface, and micron size engine. Physical functions pertain to ferro-/piezoelectricity and energy migration/storage, leading to the applications to electrodes or supercapacitors, and mechanical reinforcement. Biological functions involve artificial chaperone, transmembrane transport, nanochannels, and channel reactors. Finally, medical functions range over drug delivery, nonviral gene transfer vector, and virus trap.

A new dipeptide as a selective gelator of Cu(ii), Zn(ii), and Pb(ii)

Metallogelation was observed selectively for CuSO₄, ZnSO₄ and Pb(OAc)₂ and a dipeptide containing N-phenylglycine and l-Phe, whereas other metals and analogue dipeptides failed to form gel.

Piezoelectric Peptide and Metabolite Materials

Piezoelectric materials are important for many physical and electronic devices. Although many piezoelectric ceramics exhibit good piezoelectricity, they often show poor compatibility with biological systems that limits their biomedical applications. Piezoelectric peptide and metabolite materials benefit from their intrinsic biocompatibility, degradability, and convenient biofunctionalization and are promising candidates for biological and medical applications. Herein, we provide an account of the recent progress of research works on piezoelectric peptide and metabolite materials. This review focuses on the growth mechanism of peptide and metabolite micro- and nanomaterials. The influence of self-assembly processes on their piezoelectricity is discussed. Peptide and metabolite materials demonstrate not only outstanding piezoelectric properties but also unique electronic, optical, and physical properties, enabling their applications in nanogenerators, sensors, and optical waveguiding devices.

A Sustainable Biomineralization Approach for the Synthesis of Highly Fluorescent Ultra-Small Pt Nanoclusters

Herein we report the first example of a facile biomineralization process to produce ultra-small-sized highly fluorescent aqueous dispersions of platinum noble metal quantum clusters (Pt-NMQCs) using a multi-stimulus responsive, biomimetic intrinsically disordered protein (IDP), Rec1-resilin. We demonstrate that Rec1-resilin acts concurrently as the host, reducing agent, and stabilizer of the blue-green fluorescent Pt-NMQCs once they are being formed. The photophysical properties, quantum yield, and fluorescence lifetime measurements of the synthesized Pt-NMQCs were examined using UV-Vis and fluorescence spectroscopy. The oxidation state of the Pt-NMQCs was quantitatively analyzed using X-ray photoelectron spectroscopy. Both a small angle X-ray scattering technique and a modeling approach have been attempted to present a detailed understanding of the structure and conformational dynamics of Rec1-resilin as an IDP during the formation of the Pt-NMQCs. It has been demonstrated that the green fluorescent Pt-NMQCs exhibit a high quantum yield of ~7.0% and a lifetime of ~9.5 ns in aqueous media. The change in photoluminescence properties due to the inter-dot interactions between proximal dots and aggregation of the Pt-NMQCs by evaporation was also measured spectroscopically and discussed.

Sequence isomerism-dependent self-assembly of glycopeptide mimetics with switchable antibiofilm properties

In biological systems, diverse amino acid sequences and functional decorations endow proteins with specific functions. Functionally modified oligopeptides are attractive building blocks to assemble stimuli-responsive biomimetic superstructures for mimicking soft structures in nature and biomaterial applications. In this work, we selectively synthesized the structurally simplest isomeric tripeptides (i.e., Ala-Gly-Gly-OH, Gly-Ala-Gly-OH and Gly-Gly-Ala-OH) to demonstrate how the subtlest change in sequence isomerism influences the self-assembly of glycopeptides. To impart self-assembly capability and stimuli-responsiveness, the isomeric tripeptides were modified with a hydrophobic n-butylazobenzene tail at the N-terminal. We observed three different self-assembled 1-D morphologies (i.e., nanotwists, nanoribbons and nanofibers) from the azobenzene-glycopeptides (AGPs) under the same conditions when the position of the Ala residue was switched. Experimental methods including transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and circular dichroism (CD) spectroscopy were used to characterize the structural details of glycopeptide mimetic assemblies. Martini coarse-grained molecular dynamics (MD) simulations confirmed such structural observations and investigated the differences in assembly mechanisms. Furthermore, the glycopeptide mimetic assemblies showed a reversible disassembly-assembly process in response to temperature, light or host-guest chemistry, and can be used as switchable antibiofilm nanoagents.

Effects of the Hydrophilic-Lipophilic Balance of Alternating Peptides on Self-Assembly and Thermo-Responsive Behaviors

A series of N-substituted poly(Gly–alter–Val) peptides were successfully synthesized for the systematic evaluation of the micellization behavior of alternating peptides. Three-component polymerization employing an aldehyde, a primary ammonium chloride, and potassium isocyanoacetate afforded four alternating peptides in excellent yields. We investigated the dependence of the hydrophilic–lipophilic balance of alternating peptides on the micellization behavior. All the aqueous solutions of alternating peptides exhibited upper critical solution temperature (UCST) behaviors, strongly indicating that the alternating binary pattern would mainly contribute to the UCST behaviors. The cloud points of alternating peptides shifted to higher temperatures as the side chains became more hydrophilic, which is opposite to the trend of typical surfactants. Such unusual micellization behaviors appeared to be dependent on the quasi-stable structure of single polymer chains formed in water.

Turning a Collagenesis-Inducing Peptide Into a Potent Antibacterial and Antibiofilm Agent Against Multidrug-Resistant Gram-Negative Bacteria

Antimicrobial resistance is becoming one the most serious health threats worldwide, as it not only hampers effective treatment of infectious diseases using current antibiotics, but also increases the risks of medical procedures like surgery, transplantation, bone and dental implantation, chemotherapy, or chronic wound management. To date, there are no effective measures to tackle life-threatening nosocomial infections caused by multidrug resistant bacterial species, of which Gram-negative species within the so-called "ESKAPE" pathogens are the most worrisome. Many such bacteria are frequently isolated from severely infected skin lesions such as diabetic foot ulcers (DFU). In this connection, we are pursuing new peptide constructs encompassing antimicrobial and collagenesis-inducing motifs, to tackle skin and soft tissue infections by exerting a dual effect: antimicrobial protection and faster healing of the wound. This produced peptide 3.1-PP4 showed MIC values as low as 1.0 and 2.1 μM against Escherichia coli and Pseudomonas aeruginosa, respectively, and low toxicity to HFF-1 human fibroblasts. Remarkably, the peptide was also potent against multidrug-resistant isolates of Klebsiella pneumoniae, E. coli, and P. aeruginosa (MIC values between 0.5 and 4.1 μM), and hampered the formation of/disaggregated K. pneumoniae biofilms of resistant clinical isolates. Moreover, this notable hybrid peptide retained the collagenesis-inducing behavior of the reference cosmeceutical peptide C16-PP4 ("Matrixyl"). In conclusion, 3.1-PP4 is a highly promising lead toward development of a topical treatment for severely infected skin injuries.

Designer Peptide Amphiphiles: Self-Assembly to Applications

Peptide amphiphiles (PAs) are extremely attractive as molecular building blocks, especially in the bottom-up fabrication of supramolecular soft materials, and have potential in many important applications across various fields of science and technology. In recent years, we have designed and synthesized a large group of peptide amphiphiles. This library of PAs has the ability to self-assemble into a variety of aggregates such as fibers, nanosphere, vesicles, nanosheet, nanocups, nanorings, hydrogels, and so on. The mechanism behind the formation of such a wide range of structures is intriguing. Each system has its individual method of aggregation and results in assemblies with important applications in areas including chemistry, biology, and materials science. The aim of this feature article is to bring together our recent achievements with designer PAs with respect to their self-assembly processes and applications. Emphasis is placed on rational design, mechanistic aspects of the self-assembly processes, and the applications of these PAs. We hope that this article will provide a conceptual demonstration of the different approaches taken toward the construction of these task-specific PAs.

Self-Assembly Toolbox of Tailored Supramolecular Architectures Based on an Amphiphilic Protein Library

The molecular structuring of complex architectures and the enclosure of space are essential requirements for technical and living systems. Self-assembly of supramolecular structures with desired shape, size, and stability remains challenging since it requires precise regulation of physicochemical and conformational properties of the components. Here a general platform for controlled self-assembly of tailored amphiphilic elastin-like proteins into desired supramolecular protein assemblies ranging from spherical coacervates over molecularly defined twisted fibers to stable unilamellar vesicles is introduced. The described assembly protocols efficiently yield protein membrane-based compartments (PMBC) with adjustable size, stability, and net surface charge. PMBCs demonstrate membrane fusion and phase separation behavior and are able to encapsulate structurally and chemically diverse cargo molecules ranging from small molecules to naturally folded proteins. The ability to engineer tailored supramolecular architectures with defined fusion behavior, tunable properties, and encapsulated cargo paves the road for novel drug delivery systems, the design of artificial cells, and confined catalytic nanofactories.

Gel- and Solid-State-Structure of Dialanine and Diphenylalanine Amphiphiles: Importance of C⋅⋅⋅H Interactions in Gelation

To investigate the role of the capping group in the solution and solid-state self-assembly of short peptide amphiphiles, dialanine and diphenylalanine have been linked via the N-terminus to a benzene (phenyl) and 3-naphthyl capping groups using three different methylene linkers; (CH₂ )_n , n=0-4 for the benezene and 0, 1 and 2 for the naphthalene capping group. Atomic force microscopy (AFM), oscillatory rheology, circular dichroism (CD), and IR analysis have been employed to understand the properties of these peptide-based hydrogels. Several X-ray structures of these short peptide gelators give useful conformational information regarding packing. A comparison of these solid state structures with their gel state properties yielded greater insights into the process of self-assembly in short peptide gelators, particularly in terms of the important role of C⋅⋅⋅H interactions appear to play in determining if a short aromatic peptide does form a gel or not.

Understanding the stability of polypeptide membranes in ionic liquids: a theoretical molecular dynamics study

Stability analysis of polypeptide membranes in ionic liquids can make possible new applications of these membranes in energy storage and ionic solution separation.

Induction of adaptive immune response by self-aggregating peptides

INTRODUCTION

Recently, subunit vaccines are replacing some of the traditional vaccines because they offer a higher margin of safety. However, generally subunit vaccines have low antigenicity. Adjuvants are used in vaccine formulations to increase their immunogenicity, but current research suggests that adjuvants could induce serious side effects in susceptible individuals; therefore, the improvement of antigens and adjuvants is important.

AREAS COVERED

Here we reviewed some self-aggregating peptides (SAPs) used as antigen delivery systems. SAPs are based on a short sequence of amino acids, which have self-aggregating properties, inducing self-interaction among peptide molecules by means of non-covalent interactions to generate nanoparticles (NPs).

EXPERT COMMENTARY

SAPs increase the immunogenicity of fused/conjugated antigens because they can interact with antigen-presenting cells and induce adaptive immunity based on both humoral and cellular responses. As an example, we report an antigen delivery system based on SAPs forming NPs. These NPs are synthesized using a recombinant baculovirus. We fused the green fluorescent protein to the first 110 amino acids of polyhedrin protein from Autographa californica nucleopolyhedrovirus, which has self-aggregating properties. We showed that these NPs prompt high antibody levels without inducing inflammation, similarly to some SAPs reported here.

Conjugation of Amphiphilic Proteins to Hydrophobic Ligands in Organic Solvent

Protein-ligand conjugations are usually carried out in aqueous media in order to mimic the environment within which the conjugates will be used. In this work, we focus on the conjugation of amphiphilic variants of elastin-like polypeptide (ELP), short elastin (sEL), to poorly water-soluble compounds like OPPVs ( p-phenylenevinylene oligomers), triarylamines, and polypyridine-metal complexes. These conjugations are problematic when carried out in aqueous phase because hydrophobic ligands tend to avoid exposure to water, which in turn causes the ligand to self-aggregate and/or interact noncovalently with hydrophobic regions of the amphiphile. Ultimately, this behavior leads to low conjugation efficiency and contamination with strong noncovalent "conjugates". After exploring the solubility of sEL in various organic solvents, we have established an efficient conjugation methodology for obtaining covalent conjugates virtually free of contaminating noncovalent complexes. When conjugating carboxylated ligands to the amphiphile amines, we demonstrate that even when only one amine (the N-terminus) is present, its derivatization is 98% efficient. When conjugating amine moieties to the amphiphile carboxyls (a problematic configuration), protein multimerization is avoided, 98-100% of the protein is conjugated, and the unreacted ligand is recovered in pure form. Our syntheses occur in "one pot", and our purification procedure is a simple workup utilizing a combination of water and organic solvent extractions. This conjugation methodology might provide a solution to problems arising from solubility mismatch of protein and ligand, and it is likely to be widely applied for modification of recombinant amphiphiles used for drug delivery (PEG-antibodies, polymer-enzymes, food proteins), cell adhesion (collagen, hydrophobins), synthesis of nanostructures (peptides), and engineering of biocompatible optoelectronics (biological polymers), to cite a few.

Peroxisome-targeted Supramolecular Nanoprobes Assembled with Pyrene-labelled Peptide Amphiphiles

Despite the versatile metabolic functions of peroxisomes such as lipid synthesis and fatty acid oxidation and their relevance to genetically inherited diseases, namely, peroxisome biogenesis disorders and peroxisomal enzyme deficiency, there is not much research on peroxisome-targeting therapeutics. Herein we present supramolecular nanostructured probes based on the self-assembly of peptide amphiphiles (PAs) having peroxisome-targeting ability in mammalian cells. The PA was designed to include the peroxisome-targeting tripeptide (SKL) and a fluorescent dye (pyrene). It was revealed that the presence of the SKL-appended carboxyl terminal group of PA, the extent of α-helical nature of the peptide block, and the fibrillar morphology of nano-assemblies affected the targeting efficiency of PA supramolecular nanoprobe. The simple modification of PAs by the peroxisome-targeting strength prediction showed an enhanced peroxisome specificity, as expected. This work provides important insights into designing subcellular organelle-targeting nanoparticles for next-generation nanomedicines.

Dynamic stability of nano-fibers self-assembled from short amphiphilic A6D peptides

Self-assembly of A₆D amphiphilic peptides in explicit water is studied by using coarse-grained molecular dynamics simulations. It is observed that the self-assembly of randomly distributed A₆D peptides leads to the formation of a network of nano-fibers. Two other simulations with cylindrical nano-fibers as the initial configuration show the dynamic stability of the self-assembled nano-fibers. As a striking feature, notable fluctuations occur along the axes of the nano-fibers. Depending on the number of peptides per unit length of the nano-fiber, flat-shaped bulges or spiral shapes along the nano-fiber axis are observed at the fluctuations. Analysis of the particle distribution around the nano-fiber indicates that the hydrophobic core and the hydrophilic shell of the nano-structure are preserved in both simulations. The size of the deformations and their correlation times are different in the two simulations. This study gives new insights into the dynamics of the self-assembled nano-structures of short amphiphilic peptides.

Functional Assemblies Emerging in Complex Mixtures of Peptides and Nucleic Acid-Peptide Chimeras

Striking synergy between nucleic acids and proteins is exhibited in living cells. Whether such mutual activity can be performed using simple supramolecular nucleic acid-peptide (NA-pep) architectures remains a mystery. To shed light on this question, we studied the emergence of a primitive synergy in assemblies of short DNA-peptide chimeras. Specifically, we characterized multiple structures forming along gradual mixing trajectory, in which a peptide solution was seeded with increasing amounts of NA-pep chimeras. We report on the systematic change from β-sheet-peptide-based fibrillar architectures into the spherical structures formed by the conjugates. Remarkably, we find that through forming onion-like structures, the conjugates exhibit increased DNA hybridization stability and bind small molecules more efficiently than the peptides or DNA alone. A brief discussion highlights the implications of our findings for the production of new materials and for research on the origin of life.

Fluorinated DNA Micelles: Synthesis and Properties

Creating new functional building blocks that expand the versatility of nanostructures depends on bottom-up self-assembly of amphiphilic biomolecules. Inspired by the unique physicochemical properties of hydrophobic perfluorocarbons, coupled with the powerful functions of nucleic acids, we herein report the synthesis of a series of diperfluorodecyl-DNA conjugates (PF-DNA) which can efficiently self-assemble into micelles in aqueous solution. On the basis of the micelle structure, both target binding affinity and enzymatic resistance of the DNA probe can be enhanced. In addition, based on the hydrophobic effect, the PF-DNA micelles (PFDM) can actively anchor onto the cell membrane, offering a promising tool for cell-surface engineering. Finally, the PFDM can enter cells, which is significant for designing carriers for intracellular delivery. The combined advantages of the DNA micelle structure and the unique physicochemical properties of perfluorocarbons make these PFDM promising for applications in bioimaging and biomedicine.

Catalytic peptide assemblies

Self-assembly of molecules often results in new emerging properties. Even very short peptides can self-assemble into structures with a variety of physical and structural characteristics. Remarkably, many peptide assemblies show high catalytic activity in model reactions reaching efficiencies comparable to those found in natural enzymes by weight. In this review, we discuss different strategies used to rationally develop self-assembled peptide catalysts with natural and unnatural backbones as well as with metal-containing cofactors.

Chiral Sensing Platform Based on the Self-Assemblies of Diphenylalanine and Oxalic Acid

Molecular self-assemblies offer a promising strategy for the synthesis of advanced materials for the construction of novel chiral sensing systems, and latest innovations on such self-assemblies are focused on simple building blocks in biology such as nucleic acids, lipids, and peptides. Herein, the self-assemblies of diphenylalanine (FF) and oxalic acid (OA) were prepared as the chiral sensing device for the recognition of tryptophan (Trp) isomers. Interestingly, the self-assemblies composed of OA and FF with different charging states (neutral, positively charged, and negatively charged) exhibited quite different morphologies, resulting in significantly different chiral recognition ability toward the Trp isomers. Also, in this work, the temperature sensitivity and chiral selectivity of the proposed FF-OA self-assemblies were also studied. From a practical point of view, the FF-OA self-assemblies were finally applied for the determination of precise levels of d-Trp in the racemic mixture of Trp isomers.

Search for Fibrous Aggregates Potentially Useful in Regenerative Medicine Formed under Physiological Conditions by Self-Assembling Short Peptides Containing Two Identical Aromatic Amino Acid Residues

This study investigates the propensity of short peptides to self-organize and the influence of aggregates on cell cultures. The dipeptides were derived from both enantiomers of identical aromatic amino acids and tripeptides were prepared from two identical aromatic amino acids with one cysteine or methionine residue in the C-terminal, N-terminal, or central position. The formation or absence of fibrous structures under physiological conditions was established using Congo Red and Thioflavine T assays as well as by microscopic examination using normal and polarized light. The in vitro stability of the aggregates in buffered saline solution was assessed over 30 days. Materials with potential for use in regenerative medicine were selected based on the cytotoxicity of the peptides to the endothelial cell line EA.hy 926 and the wettability of the surfaces of the films, as well as using scanning electron microscopy. The criteria were fulfilled by H-dPhedPhe-OH, H-dCysdPhedPhe-OH, H-CysTyrTyr-OH, H-dPhedPhedCys-OH, H-TyrTyrMet-OH, and H-TyrMetTyr-OH. Our preliminary results suggest that the morphology and cell viability of L919 fibroblast cells do not depend on the stereochemistry of the self-organizing peptides.