Peptides at the Interface: Self-Assembly of Amphiphilic Designer Peptides and Their Membrane Interaction Propensity

Gold Nanoparticles-Modified 2D Self-Assembled Amphiphilic Peptide Nanosheets with High Biocompatibility and Photothermal Therapy Efficiency

Amphiphilic peptides have garnered significant attention due to their highly designable and self-assembling behaviors. Self-assembled peptides hold excellent potential in various fields such as biosensing, environmental monitoring, and drug delivery, owing to their remarkable biological, physical, and chemical properties. While nanomaterials formed by peptide self-assembly have found widespread use in biomedical applications, the development of 2D peptide nanosheets based on the self-assembly of amphiphilic peptides remains challenging in terms of rational design and morphology modulation. In this study, rationally designed amphiphilic peptide molecules are self-assembled into peptide nanosheets (PNS) under specific conditions to encapsulate gold nanoparticles (AuNPs), resulting in the formation of AuNPs/PNS hybrid materials with high photothermal conversion efficiency. The findings demonstrate that 2D PNS enhances the overall photothermal therapy effect of the nanohybrid materials due to their larger hosting area for AuNPs and higher biocompatibility. The well-designed amphiphilic peptides in this study offer insights into the structural design and functional modulation of self-assembled molecules. In addition, the constructed biomimetic-functional 2D inorganic/organic nanohybrid materials hold potential applications in biomedical engineering.

Characterization and Classification In Silico of Peptides with Dual Activity (Antimicrobial and Wound Healing)

The growing challenge of chronic wounds and antibiotic resistance has spotlighted the potential of dual-function peptides (antimicrobial and wound healing) as novel therapeutic strategies. The investigation aimed to characterize and correlate in silico the physicochemical attributes of these peptides with their biological activity. We sourced a dataset of 207 such peptides from various peptide databases, followed by a detailed analysis of their physicochemical properties using bioinformatic tools. Utilizing statistical tools like clustering, correlation, and principal component analysis (PCA), patterns and relationships were discerned among these properties. Furthermore, we analyzed the peptides' functional domains for insights into their potential mechanisms of action. Our findings spotlight peptides in Cluster 2 as efficacious in wound healing, whereas Cluster 1 peptides exhibited pronounced antimicrobial potential. In our study, we identified specific amino acid patterns and peptide families associated with their biological activities, such as the cecropin antimicrobial domain. Additionally, we found the presence of polar amino acids like arginine, cysteine, and lysine, as well as apolar amino acids like glycine, isoleucine, and leucine. These characteristics are crucial for interactions with bacterial membranes and receptors involved in migration, proliferation, angiogenesis, and immunomodulation. While this study provides a groundwork for therapeutic development, translating these findings into practical applications necessitates additional experimental and clinical research.

Stimuli-Responsive Membrane Anchor Peptide Nanofoils for Tunable Membrane Association and Lipid Bilayer Fusion

Self-assembled peptide nanostructures with stimuli-responsive features are promising as functional materials. Despite extensive research efforts, water-soluble supramolecular constructs that can interact with lipid membranes in a controllable way are still challenging to achieve. Here, we have employed a short membrane anchor protein motif (GLFD) and coupled it to a spiropyran photoswitch. Under physiological conditions, these conjugates assemble into ∼3.5 nm thick, foil-like peptide bilayer morphologies. Photoisomerization from the closed spiro (SP) form to the open merocyanine (MC) form of the photoswitch triggers rearrangements within the foils. This results in substantial changes in their membrane-binding properties, which also varies sensitively to lipid composition, ranging from reversible nanofoil reformation to stepwise membrane adsorption. The formed peptide layers in the assembly are also able to attach to various liposomes with different surface charges, enabling the fusion of their lipid bilayers. Here, SP-to-MC conversion can be used both to trigger and to modulate the liposome fusion efficiency.

Acid-Base Equilibrium and Dielectric Environment Regulate Charge in Supramolecular Nanofibers

Peptide amphiphiles are a class of molecules that can self-assemble into a variety of supramolecular structures, including high-aspect-ratio nanofibers. It is challenging to model and predict the charges in these supramolecular nanofibers because the ionization state of the peptides are not fixed but liable to change due to the acid-base equilibrium that is coupled to the structural organization of the peptide amphiphile molecules. Here, we have developed a theoretical model to describe and predict the amount of charge found on self-assembled peptide amphiphiles as a function of pH and ion concentration. In particular, we computed the amount of charge of peptide amphiphiles nanofibers with the sequence C₁₆ − V₂A₂E₂. In our theoretical formulation, we consider charge regulation of the carboxylic acid groups, which involves the acid-base chemical equilibrium of the glutamic acid residues and the possibility of ion condensation. The charge regulation is coupled with the local dielectric environment by allowing for a varying dielectric constant that also includes a position-dependent electrostatic solvation energy for the charged species. We find that the charges on the glutamic acid residues of the peptide amphiphile nanofiber are much lower than the same functional group in aqueous solution. There is a strong coupling between the charging via the acid-base equilibrium and the local dielectric environment. Our model predicts a much lower degree of deprotonation for a position-dependent relative dielectric constant compared to a constant dielectric background. Furthermore, the shape and size of the electrostatic potential as well as the counterion distribution are quantitatively and qualitatively different. These results indicate that an accurate model of peptide amphiphile self-assembly must take into account charge regulation of acidic groups through acid–base equilibria and ion condensation, as well as coupling to the local dielectric environment.

Pentacyclic triterpenes modulate liposome membrane fluidity and permeability depending on membrane cholesterol content

Since the membrane-related processes represent an integral part of the biological activities of drugs, their effect on the membrane dynamics is actually considered. In this study, we investigated the effect of pentacyclic triterpenes (TTPs), oleanolic acid (OA) and erythrodiol (ER), on the fluidity and permeability of liposomes membranes differing by their cholesterol content. All liposomes were prepared by reverse phase evaporation technique (REV). Spin-labeled liposomes exposed or not to TTPs were used for fluidity studies by using 5- and 16-doxyl stearic acids (DSA). TTPs-loaded liposomes (phospholipid:cholesterol of 1:1), and preformed vesicles exposed to TTPs were used for permeability studies by monitoring the release of sulforhodamine B (SRB) at 37 °C. The apparent release constants of SRB were determined by Higuchi model based on a biphasic curve shape (0-10 h; 10-48 h). TTPs-loaded liposomes were characterized for their size and homogeneity. Results showed that ER increased the membrane fluidity at the upper region of the membrane while the both TTPs produced a condensing effect at the deeper region of the membrane. The membrane composition was a critical parameter modulating the effect of TTPs on the membrane permeability. Also, this study consolidated the fact that a fluidizing membrane agent is not necessarily a permeabilizing-membrane compound.

Novel Descriptors Derived from the Aggregation Propensity of Di- and Tripeptides Can Predict the Critical Aggregation Concentration of Longer Peptides

Self-assembling amphiphilic peptides have recently received special attention in medicine. Nonetheless, testing the myriad of combinations generated from at least 20 coded and several hundreds of noncoded amino acids to obtain candidate sequences for each application, if possible, is time-consuming and expensive. Therefore, rapid and accurate approaches are needed to select candidates from countless combinations. In the current study, we examined three conventional descriptor sets along with a novel descriptor set derived from the simulated aggregation propensity of di- and tripeptides to model the critical aggregation concentration (CAC) of amphiphilic peptides. In contrast to the conventional descriptors, the radial kernel model derived from the novel descriptor set accurately predicted the critical aggregation concentration of the test set with a residual standard error of 0.10. The importance of aromatic side chains, as well as neighboring amino acids in the self-assembly, was emphasized by analysis of the influential descriptors. The addition of very long peptides (70-100 residues) to the data set decreased the model accuracy and changed the influential descriptors. The developed model can be used to predict the CAC of self-assembling amphiphilic peptides and also to derive rules to apply in designing novel amphiphilic peptides with desired properties.

Interactions of an Anionic Antimicrobial Peptide with Zinc(II): Application to Bacterial Mimetic Membranes

While the majority of known antimicrobial peptides are cationic, a small number consist of short Asp-rich sequences that are anionic. These require metal ions to become biologically active. Here, we report the study of the zinc complexes of the peptide GADDDDD (GAD5), an antimicrobial peptide. Using a combination of dynamic light scattering (DLS), ζ-potential, infrared, Raman, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM), we find that adding zinc ions to GAD5 forces it into a compact structure. Higher amounts of zinc ions favor a larger structure, possibly a dimer. SEM images show that zinc ions reduce the size of the fibrillar structures of GAD5. TGA curves show that the addition of zinc ions increases the thermal stability of the structure of the peptide. TGA and DSC indicate that the association of GAD5 with a zwitterionic phospholipid in the presence of zinc ions is the most stable. The stability of that complex is due to the presence of a sharp endothermic peak in the 200-300 °C range, suggesting the presence of interlamellar water that is essential to the stabilization of the structure. These results indicate that the Zn-GAD5 complex prefers the bacteria-mimicking neutral (zwitterionic) membranes. In the presence of negatively charged phospholipids, the complex remains unordered and unstable. In terms of mechanism of action, the Zn-GAD5 complex promotes a possible endocytic uptake with respect to neutral (zwitterionic) membranes while promoting membrane disruption by forming pores with respect to negatively charged phospholipids.

Targeting Acidic Diseased Tissues by pH-Triggered Membrane-Associated Peptide Folding

The advantages of targeted therapy have motivated many efforts to find distinguishing features between the molecular cell surface landscapes of diseased and normal cells. Typically, the features have been proteins, lipids or carbohydrates, but other approaches are emerging. In this discussion, we examine the use of cell surface acidity as a feature that can be exploited by using pH-sensitive peptide folding to target agents to diseased cell surfaces or cytoplasms.

Short to ultrashort peptide-based hydrogels as a platform for biomedical applications

Short peptides have attracted significant attention from researchers in the past few years due to their easy design, synthesis and characterization, diverse functionalisation possibilities, low cost, possibility to make a large range of hierarchical nanostructures and most importantly their high biocompatibility and biodegradability. Generally, short peptides are also relatively more stable than their longer variants, non-immunogenic in nature and many of them self-assemble to provide an exciting range of nanostructures, including hydrogels. Thus, the development of short peptide-based hydrogels has become an area of intense investigation. Although these hydrogels have a water content of greater than 90%, they are surprisingly highly stable structures, and thus have been used for various biomedical applications, including cell therapeutics, drug delivery, tissue engineering and regeneration, contact lenses, biosensors, and wound healing, by different researchers. Herein, we review the progress of research in the rapidly expanding field of short to ultrashort peptide-based hydrogels and their possible applications. Special attention is paid to address and review this field with regard to the stability of peptide-based hydrogels, particularly to enzymatic degradation.

Designing phenylalanine-based hybrid biological materials: controlling morphology via molecular composition

Harnessing the self-assembly of peptide sequences has demonstrated great promise in the domain of creating high precision shape-tunable biomaterials. The unique properties of peptides allow for a building block approach to material design. In this study, self-assembly of mixed systems encompassing two peptide sequences with identical hydrophobic regions and distinct polar segments is investigated. The two peptide sequences are diphenylalanine and phenylalanine-asparagine-phenylalanine. The study examines the impact of molecular composition (namely, the total peptide concentration and the relative tripeptide concentration) on the morphology of the self-assembled hybrid biological material. We report a rich polymorphism in the assemblies of these peptides and explain the relationship between the peptide sequence, concentration and the morphology of the supramolecular assembly.

Peptide self-assembly into lamellar phases and the formation of lipid-peptide nanostructures

Lipids exhibit an extraordinary polymorphism in self-assembled mesophases, with lamellar phases as biologically most relevant representative. To mimic lipid lamellar phases with amphiphilic designer peptides, seven systematically varied short peptides were engineered. Indeed, four peptide candidates (V₄D, V₄WD, V₄WD₂, I₄WD₂) readily self-assembled into lamellae in aqueous solution: small-angle X-ray scattering patterns (SAXS) revealed ordered lamellar structures with a repeat distance of ~4-5 nm. Transmission electron microscopy (TEM) images confirmed the presence of stacked sheets. Two derivatives (V₃D and V₄D₂) remained as loose aggregates dispersed in solution; one peptide (L₄WD₂) formed twisted tapes with internal lamellae and an antiparallel β-type monomer alignment. To understand the interaction of peptides with lipids they were mixed with phosphatidylcholines. Low peptide concentrations (1.1 mM) induced the formation of a heterogeneous mixture of vesicular structures: large multilamellar vesicles (d-spacing ~6.3 nm) coexisted with oligo- or unilamellar vesicles (~50 nm in diameter) and bicelle-like structures (~45 nm length, ~18 nm width). High peptide concentrations (11 mM) led to unilamellar vesicles (ULV, diameter ~260-280 nm) with a homogeneous mixing of lipids and peptides. SAXS revealed the temperature-dependent fine structure of these ULVs: at 25 °C the bilayer is in a fully interdigitated state (headgroup-to-headgroup distance dhh ~2.9 nm), whereas at 50 °C this interdigitation opens up (dhh ~3.6 nm). Our results highlight the versatility of self-assembled peptide superstructures: subtle changes in the amino acid composition are key design elements in creating peptide- or lipid-peptide nanostructures with the same richness in morphology as known from the lipid-world.