Self-Assembly, Nematic Phase Formation, and Organocatalytic Behavior of a Proline-Functionalized Lipopeptide

Enhancing pesticide detection: The role of serine in lipopeptide nanostructures and their self-assembly dynamics

In this research, we studied two novel lipopeptide sequences containing the amino acid serine (SPRWG) with one (compound 1) or two aliphatic tails (compound 2) to optimize the detection capabilities for organophosphate pesticides, specifically glyphosate. The study comprehensively explored how the incorporation of serine influences the physicochemical properties and supramolecular assembly of the lipopeptides, leading to enhanced interactions with glyphosate. Advanced analytical methods were employed to investigate these modifications, including fluorescence spectroscopy, circular dichroism, and small-angle X-ray scattering (SAXS). The results showed that serine significantly reduces the critical aggregation concentration, increases the hydrophilicity of the lipopeptides, and promotes the formation of distinct secondary structures-β-turns in compound 1 and β-sheets in compound 2. Moreover, isothermal titration calorimetry (ITC) and molecular dynamics confirmed the improved binding affinity with glyphosate strongly modulated by pH and pesticide load. Compound 1, with one alkyl chain, demonstrated notably higher catalytic activity and sensitivity linked to its pH equilibrium and structural features, marking it as particularly effective for acetylcholinesterase mimicry in pesticide detection. Density functional theory and molecular dynamics calculations showed that, when compared to the PRWG sequence, SPRWG has more unprotonated N-terminal sites due to a lower pKa, more beta-turn-like structures that improve stabilization. Besides promotes more hydrogen bonds between N-(phosphonomethyl)glycine (PNG, commonly known as glyphosate) and aggregates across a wide pH range and P/L; which explains its enhanced reactivity in Ellman's test and better inhibitory effects under the influence of PNG. Our results suggest that serine-functionalized lipopeptides have great potential as biomimetic sensors in environmental monitoring.

Inclusion of Cationic Amphiphilic Peptides in Fmoc-FF Generates Multicomponent Functional Hydrogels

Peptide building blocks have been recently proposed for the fabrication of supramolecular nanostructures able to encapsulate and in vivo deliver drugs of a different nature. The primary sequence design is essential for nanostructure property modulation, directing and affecting affinity for specific drugs. For instance, the presence of positively charged residues of lysine (K) or arginine (R) could allow improving electrostatic interactions and, in turn, the encapsulation of negatively charged active pharmaceutical ingredients, including nucleic acids. In this context, here, we describe the formulation and the multiscale structural characterization of hybrid cationic peptide containing hydrogels (HGs). In these matrices, the well-known low-molecular-weight hydrogelator, Fmoc-diphenylalanine (Fmoc-FF, Fmoc = fluorenyl methoxycarbonyl), was mixed with a library of cationic amphiphilic peptides (CAPs) differing for their alkyl chain (from C8 to C18) in a 1/1 mol/mol ratio. The structural characterization highlighted that in mixed HGs, the aggregation is guided by Fmoc-FF, whereas the cationic peptides are only partially immobilized into the hydrogelated matrix. Moreover, morphology, stiffness, topography, and toxicity are significantly affected by the length of the alkyl chain. The capability of the hydrogels to encapsulate negative drugs was evaluated using the 5-carboxyfluorescein (5-FAM) dye as a model.

Effects of proline substitution/inclusion on the nanostructure of a self-assembling β-sheet-forming peptide

Self-assembling peptides remain persistently interesting objects for building nanostructures and further assemble into macroscopic structures, e.g. hydrogels, at sufficiently high concentrations. The modulation of self-assembling β-sheet-forming peptide sequences, with a selection from the full library of amino acids, offers unique possibility for rational tuning of the resulting nanostructured morphology and topology of the formed hydrogel networks. In the present work, we explored how a known β-sheet-disassembling amino acid, proline (P), affects the self-assembly and gelation properties of amphipathic peptides. For this purpose, we modified the backbone of a known β-sheet-forming peptide, FEFKFEFK (F8, F = phenylalanine, E = glutamic acid, and K = lysine), with P to form three sequences: FEFKPEFK (FP), FEFKPEFKF (KPE) and FEFEPKFKF (EPK). The replacement of F by P in the hydrophobic face resulted in the loss of the extended β-sheet conformation of the FP peptide and no gelation at concentration as high as 100 mg mL-1, compared to typical 5 mg mL-1 concentration corresponding to F8. However, by retaining four hydrophobic phenylalanine amino acids in the sequences, hydrogels containing a partial β-sheet structure were still formed at 30 mg mL-1 for KPE (pH 4-10) and EPK (pH 2-5). TEM, AFM, small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) revealed that KPE and EPK peptides self-assemble into nanoribbons and twisted nanofibers, respectively. Molecular dynamics confirmed that the single amino acid replacement of F by P prevented the assembly of the FP peptide with respect to the stable β-sheet-forming F8 variant. Moreover, additional prolongation by F in the KPE variant and shuffling of the polar amino acid sequence in the EPK peptide supported aggregation capabilities of both variants in forming distinct shapes of individual aggregates. Although the overall number of amino acids is the same in both KPE and EPK, their shifted charge density (i.e., the chemical environment in which ionic groups reside) drives self-assembly into distinct nanostructures. The investigated structural changes can contribute to new material designs for biomedical applications and provide better understanding in the area of protein folding.

Chiral Supramolecular Self-Assembly Catalysts with Enhanced Metal Ion Interaction for Higher Enantioselectivity

Understanding the interaction between metal ions as catalytic centers and supramolecular scaffolds as chiral substrates plays an important role in developing chiral supramolecular catalysts with high enantioselectivity. Herein, we found that compared with l-norleucine chiral amphiphile (l-NorC16), l-methionine chiral amphiphile (l-MetC16) with the only heteroatom of S site difference in the hydrophilic group can form a similar supramolecular chiral nanoribbon (NR) with the bilayer structure through the self-assembly approach; yet, the interaction between the Cu(II) ion catalytic centers and supramolecular scaffolds is reinforced, favoring the chirality transfer and therefore enhancing their catalytic enantioselectivity of Diels-Alder reaction from 23% [l-NorC16-NR-Cu(II)] to 78% [l-MetC16-NR-Cu(II)]. Our work demonstrates a new strategy from the perspective of strengthening the metal ion-supramolecular scaffold interaction for the preparation of chiral supramolecular catalysts with good catalytic enantioselectivity.

Lipopeptides development in cosmetics and pharmaceutical applications: A comprehensive review

Lipopeptides are surface active, natural products of bacteria, fungi and green-blue algae origin, having diverse structures and functionalities. In analogy, a number of chemical synthesis techniques generated new designer lipopeptides with desirable features and functions. Lipopetides are self-assembly guided, supramolecular compounds which have the capacity of high-density presentation of the functional epitopes at the surface of the nanostructures. This feature contributes to their successful application in several industry sectors, including food, feed, personal care, and pharmaceutics. In this comprehensive review, the novel class of ribosomally synthesized lipopeptides is introduced alongside the more commonly occuring non-ribosomal lipopeptides. We highlight key representatives of the most researched as well as recently described lipopeptide families, with emphasis on structural features, self-assembly and associated functions. The common biological, chemical and hybrid production routes of lipopeptides, including prominent analogues and derivatives are also discussed. Furthermore, genetic engineering strategies aimed at increasing lipopeptide yields, diversity and biological activity are summarized and exemplified. With respect to application, this work mainly details the potential of lipopeptides in personal care and cosmetics industry as cleansing agents, moisturizer, anti-aging/anti-wrinkling, skin whitening and preservative agents as well as the pharmaceutical industry as anitimicrobial agents, vaccines, immunotherapy, and cancer drugs. Given that this review addresses human applications, we conclude on the topic of safety of lipopeptide formulations and their sustainable production.

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.

Cell Adhesion Motif-Functionalized Lipopeptides: Nanostructure and Selective Myoblast Cytocompatibility

The conformation and self-assembly of four lipopeptides, peptide amphiphiles comprising peptides conjugated to lipid chains, in aqueous solution have been examined. The peptide sequence in all four lipopeptides contains the integrin cell adhesion RGDS motif, and the cytocompatibility of the lipopeptides is also analyzed. Lipopeptides have either tetradecyl (C₁₄, myristyl) or hexadecyl (C₁₆, palmitoyl) lipid chains and peptide sequence WGGRGDS or GGGRGDS, that is, with either a tryptophan-containing WGG or triglycine GGG tripeptide spacer between the bioactive peptide motif and the alkyl chain. All four lipopeptides self-assemble above a critical aggregation concentration (CAC), determined through several comparative methods using circular dichroism (CD) and fluorescence. Spectroscopic methods [CD and Fourier transform infrared (FTIR) spectroscopy] show the presence of β-sheet structures, consistent with the extended nanotape, helical ribbon, and nanotube structures observed by cryogenic transmission electron microscopy (cryo-TEM). The high-quality cryo-TEM images clearly show the coexistence of helically twisted ribbon and nanotube structures for C₁₄-WGGRGDS, which highlight the mechanism of nanotube formation by the closure of the ribbons. Small-angle X-ray scattering shows that the nanotapes comprise highly interdigitated peptide bilayers, which are also present in the walls of the nanotubes. Hydrogel formation was observed at sufficiently high concentrations or could be induced by a heat/cool protocol at lower concentrations. Birefringence due to nematic phase formation was observed for several of the lipopeptides, along with spontaneous flow alignment of the lyotropic liquid crystal structure in capillaries. Cell viability assays were performed using both L929 fibroblasts and C2C12 myoblasts to examine the potential uses of the lipopeptides in tissue engineering, with a specific focus on application to cultured (lab-grown) meat, based on myoblast cytocompatibility. Indeed, significantly higher cytocompatibility of myoblasts was observed for all four lipopeptides compared to that for fibroblasts, in particular at a lipopeptide concentration below the CAC. Cytocompatibility could also be improved using hydrogels as cell supports for fibroblasts or myoblasts. Our work highlights that precision control of peptide sequences using bulky aromatic residues within "linker sequences" along with alkyl chain selection can be used to tune the self-assembled nanostructure. In addition, the RGDS-based lipopeptides show promise as materials for tissue engineering, especially those of muscle precursor cells.

Interaction between glyphosate pesticide and amphiphilic peptides for colorimetric analysis

The large-scale use of glyphosate pesticides in food production has attracted attention due to environmental damage and toxicity risks. Several regulatory authorities have established safe limits or concentrations of these pesticides in water and various food products consumed daily. The irreversible inhibition of acetylcholinesterase (AChE) activity is one of the strategies used for pesticide detection. Herein, we found that lipopeptide sequences can act as biomimetic microenvironments of AChE, showing higher catalytic activities than natural enzymes in an aqueous solution, based on IC₅₀ values. These biomolecules contain in the hydrophilic part the amino acids l-proline (P), l-arginine (R), l-tryptophan (W), and l-glycine (G), covalently linked to a hydrophobic part formed by one or two long aliphatic chains. The obtained materials are referred to as compounds 1 and 2, respectively. According to fluorescence assays, 2 is more hydrophobic than 1. The circular dichroism (CD) data present a significant difference in the molar ellipticity values, likely related to distinct conformations assumed by the proline residue in the lipopeptide supramolecular structure in solution. The morphological aspect was further characterized using small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM), which showed that compounds 1 and 2 self-assembly into cylindrical and planar core-shell structures, respectively. The mimetic AchE behaviour of lipopeptides was confirmed by Ellman's hydrolysis reaction, where the proline residue in the peptides act as a nucleophilic scavenger of organophosphate pesticides. Moreover, the isothermal titration calorimetry (ITC) experiments revealed that host-guest interactions in both systems were dominated by enthalpically-driven thermodynamics. UV-vis kinetic experiments were performed to assess the inhibition of the lipopeptide catalytic activity and the IC₅₀ values were obtained, and we found that the detection limit correlated with the increase in hydrophobicity of the lipopeptides, implying the micellization process is more favorable.

Amphiphilic self-assembly peptides: Rational strategies to design and delivery for drugs in biomedical applications

Amphiphilic self-assembling peptides are widely used in tissue and cell engineering, antimicrobials, drug-delivery systems and other biomedical fields due to their good biocompatibility, functionality, flexibility of design and synthesis, and tremendous potential as delivery carriers for drugs. Currently, the design and study of amphipathic peptides by a bottom-up method to develop new biomedical materials have become a hot topic. However, defined rules have not been established for the design and development of self-assembled peptides. Therefore, the focus of this review is to summarize and provide several rational strategies for the design and study of amphiphilic self-assembly peptides. In addition, this paper also describes the types and general self-assembling mechanism of amphipathic peptides, and outlines their applications in the delivery of hydrophobic drugs, nucleic acid drugs, peptide drugs and vaccines. Amphiphilic self-assembled peptides are expected to exploit new functional materials for drug delivery and other applications.

Structure optimization of lipopeptide assemblies for aldol reactions in an aqueous medium

Four amphiphilic peptides were synthesized, characterized, and evaluated regarding their efficiency in the catalysis of direct aldol reactions in water. The lipopeptides differ by having a double lipid chain and a guanidinium pyrrole group functionalizing one Lys side chain. All the samples are composed of the amino acids l-proline (P), l-arginine (R), or l-lysine (K) functionalized with the cationic guanidiniocarbonyl pyrrole unit (GCP), l-tryptophan (W), and l-glycine (G), covalently linked to one or two long aliphatic chains, leading to surfactant-like designs with controlled proline protonation state and different stereoselectivity. Critical aggregation concentrations (cac) were higher in the presence of the GCP group, suggesting that self-assembly depends on charge distribution along the peptide backbone. Cryogenic Transmission Electron Microscopy (Cryo-TEM) and Small Angle X-ray Scattering (SAXS) showed a rich polymorphism including spherical, cylindrical, and bilayer structures. Molecular dynamics simulations performed to assess the lipopeptide polymorphs revealed an excellent agreement with core-shell arrangements derived from SAXS data and provided an atomistic view of the changes incurred by modifying head groups and lipid chains. The resulting nanostructures behaved as excellent catalysts for aldol condensation reactions, in which superior conversions (>99%), high diastereoselectivities (ds = 94 : 6), and enantioselectivities (ee = 92%) were obtained. Our findings contribute to elucidate the effect of nanoscale organization of lipopeptide assemblies in the catalysis of aldol reactions in an aqueous environment.

Biocatalysts Based on Peptide and Peptide Conjugate Nanostructures

Peptides and their conjugates (to lipids, bulky N-terminals, or other groups) can self-assemble into nanostructures such as fibrils, nanotubes, coiled coil bundles, and micelles, and these can be used as platforms to present functional residues in order to catalyze a diversity of reactions. Peptide structures can be used to template catalytic sites inspired by those present in natural enzymes as well as simpler constructs using individual catalytic amino acids, especially proline and histidine. The literature on the use of peptide (and peptide conjugate) α-helical and β-sheet structures as well as turn or disordered peptides in the biocatalysis of a range of organic reactions including hydrolysis and a variety of coupling reactions (e.g., aldol reactions) is reviewed. The simpler design rules for peptide structures compared to those of folded proteins permit ready ab initio design (minimalist approach) of effective catalytic structures that mimic the binding pockets of natural enzymes or which simply present catalytic motifs at high density on nanostructure scaffolds. Research on these topics is summarized, along with a discussion of metal nanoparticle catalysts templated by peptide nanostructures, especially fibrils. Research showing the high activities of different classes of peptides in catalyzing many reactions is highlighted. Advances in peptide design and synthesis methods mean they hold great potential for future developments of effective bioinspired and biocompatible catalysts.

Low molecular weight self-assembling peptide-based materials for cell culture, antimicrobial, anti-inflammatory, wound healing, anticancer, drug delivery, bioimaging and 3D bioprinting applications

In this review, we have focused on the design and development of low molecular weight self-assembling peptide-based materials for various applications including cell proliferation, tissue engineering, antibacterial, antifungal, anti-inflammatory, anticancer, wound healing, drug delivery, bioimaging and 3D bioprinting. The first part of the review describes about stimuli and various noncovalent interactions, which are the key components of various self-assembly processes for the construction of organized structures. Subsequently, the chemical functionalization of the peptides has been discussed, which is required for the designing of self-assembling peptide-based soft materials. Various low molecular weight self-assembling peptides have been discussed to explain the important structural features for the construction of defined functional nanostructures. Finally, we have discussed various examples of low molecular weight self-assembling peptide-based materials for cell culture, antimicrobial, anti-inflammatory, anticancer, wound healing, drug delivery, bioimaging and 3D bioprinting applications.