Altering Peptide Fibrillization by Polymer Conjugation

A strategy is presented that exploits the ability of synthetic polymers of different nature to disturb the strong self-assembly capabilities of amyloid based β-sheet forming peptides. Following a convergent approach, the peptides of interest were synthesized via solid-phase peptide synthesis (SPPS) and the polymers via reversible addition–fragmentation chain transfer (RAFT) polymerization, followed by a copper­(I) catalyzed azide–alkyne cycloaddition (CuAAC) to generate the desired peptide–polymer conjugates. This study focuses on a modified version of the core sequence of the β-amyloid peptide (Aβ), Aβ(16–20) (KLVFF). The influence of attaching short poly­(<i>N</i>-isopropylacrylamide) and poly­(hydroxyethylacrylate) to the peptide sequences on the self-assembly properties of the hybrid materials were studied via infrared spectroscopy, TEM, circular dichroism and SAXS. The findings indicate that attaching these polymers disturbs the strong self-assembly properties of the biomolecules to a certain degree and permits to influence the aggregation of the peptides based on their β-sheets forming abilities. This study presents an innovative route toward targeted and controlled assembly of amyloid-like fibers to drive the formation of polymeric nanomaterials

Tuning Self-Assembled Nanostructures Through Enzymatic Degradation of a Peptide Amphiphile

The enzymatic cleavage of a peptide amphiphile (PA) is investigated. The self-assembly of the cleaved products is distinct from that of the PA substrate. The PA C₁₆-KKFFVLK is cleaved by α-chymotrypsin at two sites leading to products C₁₆-KKF with FVLK and C₁₆-KKFF with VLK. The PA C₁₆-KKFFVLK forms nanotubes and helical ribbons at room temperature. Both PAs C₁₆-KKF and C₁₆-KKFF corresponding to cleavage products instead self-assemble into 5–6 nm diameter spherical micelles, while peptides FVLK and VLK do not adopt well-defined aggregate structures. The secondary structures of the PAs and peptides are examined by FTIR and circular dichroism spectroscopy and X-ray diffraction. Only C₁₆-KKFFVLK shows substantial β-sheet secondary structure, consistent with its self-assembly into extended aggregates, based on PA layers containing hydrogen-bonded peptide headgroups. This PA also exhibits a thermoreversible transition to twisted tapes on heating

Slow-Release RGD-Peptide Hydrogel Monoliths

We report on the formation of hydrogel monoliths formed by functionalized peptide Fmoc-RGD (Fmoc: fluorenylmethoxycarbonyl) containing the RGD cell adhesion tripeptide motif. The monolith is stable in water for nearly 40 days. The gel monoliths present a rigid porous structure consisting of a network of peptide fibers. The RGD-decorated peptide fibers have a β-sheet secondary structure. We prove that Fmoc-RGD monoliths can be used to release and encapsulate material, including model hydrophilic dyes and drug compounds. We provide the first insight into the correlation between the absorption and release kinetics of this new material and show that both processes take place over similar time scales

Structure Variation and Evolution in Microphase-Separated Grafted Diblock Copolymer Films

The phase behavior of grafted d-polystyrene-<i>block</i>-poly(methyl methacrylate) diblock copolymer films is examined, with particular focus on the effect of solvent and annealing time. It was observed that the films undergo a two-step transformation from an initially disordered state, through an ordered metastable state, to the final equilibrium configuration. It was also found that altering the solvent used to wash the films, or complete removal of the solvent prior to thermal annealing using supercritical CO₂, could influence the structure of the films in the metastable state, though the final equilibrium state was unaffected. To aid in the understanding to these experimental results, a series of self-consistent field theory calculations were done on a model diblock copolymer brush containing solvent. Of the different models examined, those which contained a solvent selective for the grafted polymer block most accurately matched the observed experimental behavior. We hypothesize that the structure of the films in the metastable state results from solvent enrichment of the film near the film/substrate interface in the case of films washed with solvent or faster relaxation of the nongrafted block for supercritical CO₂ treated (solvent free) films. The persistence of the metastable structures was attributed to the slow reorganization of the polymer chains in the absence of solvent

Tetragonal and Helical Morphologies from Polyferrocenylsilane Block Polyelectrolytes via Ionic Self-Assembly

The use of ionic self-assembly, a facile non-covalent approach, to access non-conventional block copolymer morphologies, including tetragonal and helical structures, from a combination of polyferrocenylsilane diblock copolymer polyelectrolytes and AOT-based surfactants, is described

Interaction between a Cationic Surfactant-like Peptide and Lipid Vesicles and Its Relationship to Antimicrobial Activity

We investigate the properties of an antimicrobial surfactant-like peptide (Ala)₆(Arg), A₆R, containing a cationic headgroup. The interaction of this peptide with zwitterionic (DPPC) lipid vesicles is investigated using a range of microscopic, X-ray scattering, spectroscopic, and calorimetric methods. The β-sheet structure adopted by A₆R is disrupted in the presence of DPPC. A strong effect on the small-angle X-ray scattering profile is observed: the Bragg peaks from the DPPC bilayers in the vesicle walls are eliminated in the presence of A₆R and only bilayer form factor peaks are observed. All of these observations point to the interaction of A₆R with DPPC bilayers. These studies provide insight into interactions between a model cationic peptide and vesicles, relevant to understanding the action of antimicrobial peptides on lipid membranes. Notably, peptide A₆R exhibits antimicrobial activity without membrane lysis

Supporting Information from Peptide-based ambidextrous bifunctional gelator: applications in oil spill recovery and removal of toxic organic dyes for waste water management

Supporting Information Peptide based Ambidextrous Bifunctional Gelator: Applications in Oil Spill Recovery and Removal of Toxic Organic Dyes for Waste Water Managemen

Assembly of an Injectable Noncytotoxic Peptide-Based Hydrogelator for Sustained Release of Drugs

A new synthetic tripeptide-based hydrogel has been discovered at physiological pH and temperature. This hydrogel has been thoroughly characterized using different techniques including field emission scanning electron microscopic (FE-SEM) and high-resolution transmission electron microscopic (HR-TEM) imaging, small- and wide-angle X-ray diffraction analyses, FT-IR, circular dichroism, and rheometric analyses. Moreover, this gel exhibits thixotropy and injectability. This hydrogel has been used for entrapment and sustained release of an antibiotic vancomycin and vitamin B₁₂ at physiological pH and temperature for about 2 days. Interestingly, MTT assay of these gelator molecules shows almost 100% cell viability of this peptide gelator, indicating its noncytotoxicity

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

Aβ1-42 oligomers formed in the presence of IDEQ are not neurotoxic.

<p>(<b>A</b>) Representative AFM images showing the size and morphology of Aβ1-42 neurotoxic species. Left, Aβ1-42 incubated alone for 4 days. Approximately spherical species of ∼20–30 nm are indicated by arrowheads. Rods and short protofibrils are depicted by arrows. Inset: a larger Aβ1-42 protofibril is shown. Right; Aβ1-42 incubated in the presence of IDEQ at a 1∶10 molar ratio (IDEQ: Aβ) showing larger aggregates of 50–60 nm (arrowheads) and rods with lengths of ∼100–120 nm (arrows). (<b>B</b>) Representative immunofluorescence of primary differentiated neurons exposed to vehicle, Aβ1-42 alone or Aβ1-42 pre-incubated with IDEQ from top to bottom, as indicated. White arrows point at neuronal processes. Bars  = 30 μM. (<b>C</b>) Analysis of neuronal processes under the conditions as shown in panel (<b>A</b>). Bars represent the mean ± SEM of processes' lengths as measured from the centre of the neuronal body * p<0.01, one-way ANOVA, Tukey post-hoc test. (<b>D</b>) Viability of mature primary neurons after the indicated treatments as assessed by MTT reduction. * p<0.05, one-way ANOVA, Tukey post-hoc test. Results are shown for three independent experiments.</p