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We demonstrate that a conserved coronavirus spike protein peptide forms amyloid structures, differing from the native helical conformation and not predicted by amyloid aggregation algorithms. We investigate the conformation and aggregation of peptide RSAIEDLLFDKV, which is a sequence common to many animal and human coronavirus spike proteins. This sequence is part of a native α-helical S2 glycoprotein domain, close to and partly spanning the fusion sequence. This peptide aggregates into β-sheet amyloid nanotape structures close to the calculated pI = 4.2, but forms disordered monomers at high and low pH. The β-sheet conformation revealed by FTIR and circular dichroism (CD) spectroscopy leads to peptide nanotape structures, imaged using transmission electron microscopy (TEM) and probed by small-angle X-ray scattering (SAXS). The nanotapes comprise arginine-coated bilayers. A Congo red dye UV–vis assay is used to probe the aggregation of the peptide into amyloid structures, which enabled the determination of a critical aggregation concentration (CAC). This peptide also forms hydrogels under precisely defined conditions of pH and concentration, the rheological properties of which were probed. The observation of amyloid formation by a coronavirus spike has relevance to the stability of the spike protein conformation (or its destabilization via pH change), and the peptide may have potential utility as a functional material. Hydrogels formed by coronavirus peptides may also be of future interest in the development of slow-release systems, among other applications.

A dipeptide-based synthetic amphiphile bearing a myristyl chain has been found to form hydrogels in the pH range 6.9–8.5 and organogels in various organic solvents including petroleum ether, diesel, kerosene, and petrol. These organogels and hydrogels have been thoroughly studied and characterized by different techniques including high-resolution transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and rheology. It has been found that the xerogel obtained from the peptide gelator can trap various toxic organic dyes from wastewater efficiently. Moreover, the hydrogel has been used to remove toxic heavy metal ions Pb2+ and Cd2+ from wastewater. Dye adsorption kinetics has been studied, and it has been fitted by using the Freundlich isotherm equation. Interestingly, the gelator amphiphilic peptide gels fuel oil, kerosene, diesel, and petrol in a biphasic mixture of salt water and oil within a few seconds. This indicates that these gels not only may find application in oil spill recovery but also can be used to remove toxic organic dyes and hazardous toxic metal ions from wastewater. Moreover, the gelator can be recycled several times without significant loss of activity, suggesting the sustainability of this new gelator. This holds future promise for environmental remediation by using peptide-based gelators.

Morphological, spectroscopic and scattering studies of the self-assembly and aggregation process of mixtures of [RF]4 and P[RF]4 peptides (where: R = arginine; F = phenylalanine; P = proline), in solution and as hydrogels, were performed to obtain information about polymorphism. CD data confirmed a β-sheet secondary structure conformation for the solutions and TEM images revealed nanofibers with diameters of ~ 10 nm and micrometer lengths. SAXS curves were fitted using a mass fractal-component and a long cylinder shell form factor for the liquid samples, and only a long cylinder shell form factor for the gels. Increasing the P[RF]4 content in the systems leads to a reduction in cylinder radius and core density scattering, suggesting an increase in packing of the peptide molecules; however, the opposite effect was observed for the gels. Remarkably, the gels are birefringent, indicating nematic ordering of the gel fibrils. These compounds show potential as catalysts in the asymmetric aldol reactions, with cyclohexanone and p-nitrobenzaldehyde in aqueous media. A moderate conversion (36.9 %) and a good stereoselectivity (69:31) were observed for the system containing only [RF]4, and with the increase of the P[RF]4, a considerable decrease of the conversion was observed, suggesting differences in the self-assembly and packing factor. Rheological measurements were performed to determine the shear moduli for the soft gels. These model amyloid peptides demonstrate a range of tunable self-assembly behaviors and additionally have potential as biocatalysts.

Upon changing the position, nature and number of the halogen atoms, the same amyloidogenic peptide self-assembles into different nanostructures., Amyloid peptides yield a plethora of interesting nanostructures though difficult to control. Here we report that depending on the number, position, and nature of the halogen atoms introduced into either one or both phenylalanine benzene rings of the amyloid β peptide-derived core-sequence KLVFF, four different architectures were obtained in a controlled manner. Our findings demonstrate that halogenation may develop as a general strategy to engineer amyloidal peptide self-assembly and obtain new amyloidal nanostructures.

Penetratin is a short Trojan peptide that attracts great interest in biomedical research for its capacity to translocate biological membranes. Herein, we study in detail both self-assembly and intracellular delivery of DNA by the heptamer KIWFQNR, a truncated peptide derived from Penetratin. This shortened sequence possesses a unique design with bolaamphiphilic characteristics that preserves the longest noncationic amino acid portion found in Penetratin. These features convey amphipathicity to assist self-assembly and make it a suitable model for exploring the role of hydrophobic residues for peptide interaction and cell uptake. We show that the fragment forms peptiplexes (i.e., peptide–DNA complexes), and aggregates into long nanofibers with clear β-sheet signature. The supramolecular structure of nanofibers is likely composed of DNA cores surrounded by a peptide shell to which the double helix behaves as a template and induces fibrillization. A nucleation and growth mechanism proceeding through liquid–liquid phase separation of coacervates is proposed for describing the self-assembly of peptiplexes. We also demonstrate that peptiplexes deliver double-stranded 200 bp DNA into HeLa cells, indicating its potential for preparing non-viral vectors for oligonucleotides through noncovalent strategies. Since the main structural features of native Penetratin are conserved in this simpler fragment, our findings also highlight the role of uncharged amino acids for structuration, and thus for the ability of Penetratin to cross cell membranes.

The self-assembly and biocatalytic activity of the proline-functionalized lipopeptide PRW-NH-C16 are examined, and compared to that of the related PRW-O-C16 lipopeptide, which differs in having an ester linker between the lipid chain and tripeptide headgroup instead of an amide linker. Lipopeptide PRW-NH-C16 self-assembles into spherical micelles above a critical aggregation concentration, similar to the behaviour of PRW-O-C16 reported previously [B.M. Soares et al. Phys. Chem. Chem. Phys., 2017, 19, 1181—1189]. However, PRW-NH-C16 shows improved catalytic activity in a model aldol reaction. In addition, we explore incorporation of the biocatalytic lipopeptide into lipid cubosomes. SAXS shows that increasing lipopeptide concentration leads to an expansion of the monoolein cubosome lattice spacing, and loss of long-range cubic order as the lipopeptide is encapsulated in the cubosomes. At higher loadings of lipopeptide, reduced cubosome formation is observed at the expense of vesicle formation. Our results show that the peptide-lipid chain linker does not influence self-assembly but does impart improved biocatalytic activity. Furthermore, we show that lipopeptides can be incorporated into lipid cubosomes, leading to restructuring into vesicles at high loadings. These findings point the way towards the future development of bioactive lipopeptide assemblies and slow release cubosome-based delivery systems.