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The self-assembly of two derivatives of KLVFF, a fragment Aβ(16-20) of the amyloid beta (Aβ) peptide, is investigated and recovery of viability of neuroblastoma cells exposed to Aβ (1-42) is observed at sub-stoichiometric peptide concentrations. Fluorescence assays show that NH 2 -KLVFF-CONH 2 undergoes hydrophobic collapse and amyloid formation at the same critical aggregation concentration (cac). In contrast, NH 2 -K(Boc)LVFF-CONH 2 undergoes hydrophobic collapse at a low concentration, followed by amyloid formation at a higher cac. These findings are supported by the β-sheet features observed by FTIR. Electrospray ionization mass spectrometry indicates that NH 2 -K(Boc)LVFF-CONH 2 forms a significant population of oligomeric species above the cac. Cryo-TEM, used together with SAXS to determine fibril dimensions, shows that the length and degree of twisting of peptide fibrils seem to be influenced by the net peptide charge. Grazing incidence X-ray scattering from thin peptide films shows features of β-sheet ordering for both peptides, along with evidence for lamellar ordering of NH 2 -KLVFF-CONH 2. This work provides a comprehensive picture of the aggregation properties of these two KLVFF derivatives and shows their utility, in unaggregated form, in restoring the viability of neuroblastoma cells against Aβ-induced toxicity. Fil: Castelletto, V.. University of Reading; Reino Unido Fil: Ryumin, P.. University of Reading; Reino Unido Fil: Cramer, R.. University of Reading; Reino Unido Fil: Hamley, I.W.. University of Reading; Reino Unido Fil: Taylor, M.. University of Lancaster; Reino Unido Fil: Allsop, D.. University of Lancaster; Reino Unido Fil: Reza, M.. Aalto University; Finlandia Fil: Ruokolainen, J.. Aalto University; Finlandia Fil: Arnold, T.. Diamond Light Source Ltd.,Harwell Science and Innovation Campus; Reino Unido Fil: Hermida Merino, D.. European Synchrotron Radiation Facility; Francia Fil: Garcia, Corina Ileana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentina Fil: Leal, Maria Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentina Fil: Castaño, Eduardo Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentina

We examine the self-assembly of a peptide A6H comprising a hexa-alanine sequence A6 with a histidine (H) "head group", which chelates Zn(2+) cations. We study the self-assembly of A6H and binding of Zn(2+) ions in ZnCl2 solutions, under acidic and neutral conditions. A6H self-assembles into nanotapes held together by a β-sheet structure in acidic aqueous solutions. By dissolving A6H in acidic ZnCl2 solutions, the carbonyl oxygen atoms in A6H chelate the Zn(2+) ions and allow for β-sheet formation at lower concentrations, consequently reducing the onset concentration for nanotape formation. A6H mixed with water or ZnCl2 solutions under neutral conditions produces short sheets or pseudocrystalline tapes, respectively. The imidazole ring of A6H chelates Zn(2+) ions in neutral solutions. The internal structure of nanosheets and pseudocrystalline sheets in neutral solutions is similar to the internal structure of A6H nanotapes in acidic solutions. Our results show that it is possible to induce dramatic changes in the self-assembly and chelation sites of A6H by changing the pH of the solution. However, it is likely that the amphiphilic nature of A6H determines the internal structure of the self-assembled aggregates independent from changes in chelation.

© The Royal Society of Chemistry. Macroscopic capsules, with tunable properties based on hierarchical self-assembly on multiple lengthscales, are prepared from the co-operative self-assembly of polysaccharide and peptide amphiphiles. Different formulations can be used to create flexible membrane sacs in solution, soft capsules or rigid free-standing capsules. Samples are prepared by injecting a solution containing sodium alginate, with or without graphene oxide (GO), into a matrix consisting of a solution containing the peptide amphiphile PA C16-KKFF (K: lysine, F: phenylalanine), with or without CaCl2. Graphene oxide is added to the hybrid materials to modulate the mechanical properties of the capsules. Injection of sodium alginate solution into a pure PA matrix provides a flexible membrane sac in solution, while injection of NaAlg/GO solution into a PA matrix gives a soft capsule. Alternatively, a rigid free-standing capsule is made by injecting a NaAlg/GO solution into a PA + CaCl2 matrix solution. A comprehensive insight into the hierarchical order within the capsules is provided through analysis of X-ray scattering data. A novel “Langmuir-Blodgett” mechanism is proposed to account for the formation of the sacs and capsules as the alginate solution is injected at the interface of the PA solution. The capsules show a unique antibacterial effect specific for the Gram positive bacterium Listeria monocytogenes, which is an important human pathogen. The hybrid nanostructured capsules thus have remarkable bioactivity and due to their tunable structural and functional properties are likely to have a diversity of other future applications.

Macroscopic capsules, with tunable properties based on hierarchical self-assembly on multiple lengthscales, are prepared from the co-operative self-assembly of polysaccharide and peptide amphiphiles. Different formulations can be used to create flexible membrane sacs in solution, soft capsules or rigid free-standing capsules. Samples are prepared by injecting a solution containing sodium alginate, with or without graphene oxide (GO), into a matrix consisting of a solution containing the peptide amphiphile PA C16-KKFF (K: lysine, F: phenylalanine), with or without CaCl2. Graphene oxide is added to the hybrid materials to modulate the mechanical properties of the capsules. Injection of sodium alginate solution into a pure PA matrix provides a flexible membrane sac in solution, while injection of NaAlg/GO solution into a PA matrix gives a soft capsule. Alternatively, a rigid free-standing capsule is made by injecting a NaAlg/GO solution into a PA + CaCl2 matrix solution. A comprehensive insight into the hierarchical order within the capsules is provided through analysis of X-ray scattering data. A novel “Langmuir-Blodgett” mechanism is proposed to account for the formation of the sacs and capsules as the alginate solution is injected at the interface of the PA solution. The capsules show a unique antibacterial effect specific for the Gram positive bacterium Listeria monocytogenes, which is an important human pathogen. The hybrid nanostructured capsules thus have remarkable bioactivity and due to their tunable structural and functional properties are likely to have a diversity of other future applications.

© 2017 American Chemical Society. Chirality and morphology are essential factors for protein function and interactions with other biomacromolecules. Extracellular matrix (ECM) proteins are also similar to other proteins in this sense; however, the complexity of the natural ECM makes it difficult to study these factors at the cellular level. The synthetic peptide nanomaterials harbor great promise in mimicking specific ECM molecules as model systems. In this work, we demonstrate that mechanosensory responses of stem cells are directly regulated by the chirality and morphology of ECM-mimetic peptide nanofibers with strictly controlled characteristics. Structural signals presented on l-amino acid containing cylindrical nanofibers (l-VV) favored the formation of integrin β1-based focal adhesion complexes, which increased the osteogenic potential of stem cells through the activation of nuclear YAP. On the other hand, twisted ribbon-like nanofibers (l-FF and d-FF) guided the cells into round shapes and decreased the formation of focal adhesion complexes, which resulted in the confinement of YAP proteins in the cytosol and a corresponding decrease in osteogenic potential. Interestingly, the d-form of twisted-ribbon like nanofibers (d-FF) increased the chondrogenic potential of stem cells more than their l-form (l-FF). Our results provide new insights into the importance and relevance of morphology and chirality of nanomaterials in their interactions with cells and reveal that precise control over the chemical and physical properties of nanostructures can affect stem cell fate even without the incorporation of specific epitopes.

International audience; The self-assembly in aqueous solution of three novel telechelic conjugates comprising a central hydrophilic polymer and short (trimeric or pentameric) tyrosine end-caps has been investigated. Two of the conjugates have a central poly(oxyethylene) (polyethylene oxide, PEO) central block with different molar masses. The other conjugate has a central poly(l-alanine) (PAla) sequence in a purely amino-acid based conjugate. All three conjugates self-assemble into beta-sheet based fibrillar structures, although the fibrillar morphology revealed by cryogenic-TEM is distinct for the three polymers-in particular the Tyr5-PEO6k-Tyr5 forms a population of short straight fibrils in contrast to the more diffuse fibril aggregates observed for Tyr5-PEO2k-Tyr5 and Tyr3-PAla-Tyr3. Hydrogel formation was not observed for these samples (in contrast to prior work on related systems) up to quite high concentrations, showing that it is possible to prepare solutions of peptide-polymer-peptide conjugates with hydrophobic end-caps without conformational constraints associated with hydrogelation. The Tyr5-PEO6k-Tyr5 shows significant PEO crystallization upon drying in contrast to the Tyr5-PEO2k-Tyr5 conjugate. Our findings point to the remarkable ability of short hydrophobic peptide end groups to modulate the self-assembly properties of polymers in solution in model peptide-capped associative polymers. Retention of fluidity at high conjugate concentration may be valuable in potential future applications of these conjugates as bioresponsive or biocompatible materials, for example exploiting the enzyme-responsiveness of the tyrosine end-groups

We examine the self-assembly of a peptide A6H\ud comprising a hexa-alanine sequence A6 with a histidine (H) “head group”, which chelates Zn2+ cations. We study the self assembly of A6H and binding of Zn2+ ions in ZnCl2 solutions, under acidic and neutral conditions. A6H self-assembles into nanotapes held together by a β-sheet structure in acidic aqueous solutions. By dissolving A6H in acidic ZnCl2 solutions, the carbonyl oxygen atoms in A6H chelate the Zn2+ ions and allow for β-sheet formation at lower concentrations, consequently reducing the onset concentration for nanotape formation. A6H mixed with water or ZnCl2 solutions under neutral conditions produces short sheets or pseudocrystalline tapes, respectively. The imidazole ring of A6H chelates Zn2+ ions in neutral solutions. The internal structure of nanosheets and pseudocrystalline sheets in neutral solutions is similar to the internal structure of A6H nanotapes in acidic solutions. Our results show that it is possible to induce dramatic changes in the self-assembly and chelation sites of A6H by changing the pH of the solution. However, it is likely that the amphiphilic nature of A6H determines the internal structure of the self-assembled aggregates independent from changes in chelation.

The self-assembly in aqueous solution of a PEG-peptide conjugate is studied by spectroscopy, electron microscopy, rheology and small-angle X-ray and neutron scattering (SAXS and SANS). The peptide fragment, FFKLVFF is based on fragment KLVFF of the amyloid β-peptide, Aβ-(16-20), extended by two hydrophobic phenylalanine units. This is conjugated to PEG which confers water solubility and leads to distinct self-assembled structures. Small-angle scattering reveals the formation of cylindrical fibrils comprising a peptide core and PEG corona. This constrained structure leads to a model parallel β-sheet self-assembled structure with a radial arrangement of β sheets. On increasing concentration, successively nematic and hexagonal columnar phases are formed. The flow-induced alignment of both structures was studied in situ by SANS using a Couette cell. Shear-in-duced alignment is responsible for the shear thinning behaviour observed by dynamic shear rheometry. Incomplete recovery of moduli after cessation of shear is consistent with the observation from SANS of retained orientation in the sample. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

The introduction of ionic single-tailed surfactants to aqueous solutions of EO18BO10 [EO = poly(ethylene oxide), BO = poly(1,2-butylene oxide), subscripts denote the number of repeating units] leads to the formation of vesicles, as probed by laser scanning confocal microscopy. Dynamic light scattering showed that the dimensions of these aggregates at early stages of development do not depend on the sign of the surfactant head group charge. Small-angle X-ray scattering (SAXS) analysis indicated the coexistence of smaller micelles of different sizes and varying polymer content in solution. In strong contrast to the dramatic increase of size of dispersed particles induced by surfactants in dilute solution, the d-spacing of corresponding mesophases reduces monotonically upon increasing surfactant loading. This effect points to the suppression of vesicles as a consequence of increasing ionic strength in concentrated solutions. Maximum enhancements of storage modulus and thermal stability of hybrid gels take place at different compositions, indicating a delicate balance between the number and size of polymer-poor aggregates (population increases with surfactant loading) and the number and size of polymer-surfactant complexes (number and size decrease in high surfactant concentrations). © 2008 American Chemical Society.

The self-assembly of a fragment of the amyloid β peptide that has been shown to be critical in amyloid fibrillization has been studied in aqueous solution. There are conflicting reports in the literature on the fibrillization of Aβ (16-20), i.e., KLVFF, and our results shed light on this. In dilute solution, self-assembly of NH2-KLVFF-COOH is strongly influenced by aromatic interactions between phenyl-alanine units, as revealed by UV spectroscopy and circular dichroism. Fourier transform infrared (FTIR) spectroscopy reveals β-sheet features in spectra taken for more concentrated solutions and also dried films. X-ray diffraction and cryo-transmission electron microscopy (cryo-TEM) provide further support for β-sheet amyloid fibril formation. A comparison of cryo-TEM images with those from conventional dried and negatively stained TEM specimens highlights the pronounced effects of sample preparation on the morphology. A comparison of FTIR data for samples in solution and dried samples also highlights the strong effect of drying on the self-assembled structure. In more concentrated phosphate-buffered saline (PBS) solution, gelation of NH2-KLVFF-COOH is observed. This is believed to be caused by screening of the electrostatic charge on the peptide, which enables β sheets to aggregate into a fibrillar gel network. The rheology of the hydrogel is probed, and the structure is investigated by light scattering and small-angle X-ray scattering. © 2008 American Chemical Society.

The interactions of bovine serum albumin (BSA) with three ethylene oxide/ butylene oxide (E/B) copolymers having different block lengths and varying molecular architectures is examined in this study in aqueous solutions. Dynamic light scattering (DLS) indicates the absence of BSA-polymer binding in micellar systems of copolymers with lengthy hydrophilic blocks. On the contrary, stable protein-polymer aggregates were observed in the case of E18B10 block copolymer. Results from DLS and SAXS suggest the dissociation of E/B copolymer micelles in the presence of protein and the absorption of polymer chains to BSA surface. At high protein loadings, bound BSA adopts a more compact conformation in solution. The secondary structure of the protein remains essentially unaffected even at high polymer concentrations. Raman spectroscopy was used to give insight to the configurations of the bound molecules in concentrated solutions. In the vicinity of the critical gel concentration of E18B10 introduction of BSA can dramatically modify the phase diagram, inducing a gel-sol-gel transition. The overall picture of the interaction diagram of the E18B10-BSA reflects the shrinkage of the suspended particles due to destabilization of micelles induced by BSA and the gelator nature of the globular protein. SAXS and rheology were used to further characterize the structure and flow behavior of the polymer-protein hybrid gels and sols. © 2008 American Chemical Society.

In this work, we report the formation of complexes by self-assembly of bovine serum albumin (BSA) with a poly(ethylene glycol) lipid conjugate (PEG2000-PE) in phosphate saline buffer solution (pH 7.4). Three different sets of samples have been studied. The BSA concentration remained fixed (1, 0.01, or 0.001 wt % BSA) within each set of samples, while the PEG2000-PE concentration was varied. Dynamic light scattering (DLS), rheology, and small-angle X-ray scattering (SAXS) were used to study samples with 1 wt % BSA. DLS showed that BSA/ PEG2000-PE aggregates have a size intermediate between a BSA monomer and a PEG2000-PE micelle. Rheology suggested that BSA/PEG2000-PE complexes might be surrounded by a relatively compact PEG-lipid shell, while SAXS results showed that depletion forces do not take an important role in the stabilization of the complexes. Samples containing 0.01 wt % BSA were studied by circular dichroism (CD) and ultraviolet fluorescence spectroscopy (UV). UV results showed that at low concentrations of PEG-lipid, PEG2000-PE binds to tryptophan (Trp) groups in BSA, while at high concentrations of PEG-lipid the Trp groups are exposed to water. CD results showed that changes in Trp environment take place with a minimal variation of the BSA secondary structure elements. Finally, samples containing 0.001 wt % BSA were studied by zeta-potential experiments. Results showed that steric interactions might play an important role in the stabilization of the BSA/PEG2000-PE complexes. © 2007 American Chemical Society.

The structure of three different ABC triblock star terpolymers in aqueous solution has been investigated by small-angle x-ray scattering (SAXS). The form factor was modeled using an analytical expression for a Gaussian homopolymer star since the SAXS data were not sensitive to the electron density differences between blocks. The interparticle structure factor could be described by the hard sphere model. The radius of gyration of the stars is obtained by modeling of the SAXS data. The overall size of the stars is sensitive to the degree of hydrophobicity of the block located in the center of the star. The dimensions of the starblock terpolymers are compared with those obtained from light-scattering experiments. 43 B 1 43 57 Cited By :2

The liquid-solid transition between micellar phases of a diblock copolymer solution in water was studied using small-angle x-ray scattering (SAXS). The phase transitions were identified by dynamic shear rheometry and mobility measurements. The transition from liquid micellar solution to solid cubic crystal was described using the hard sphere model. Results showed the presence of a coexistence region between hard sphere fluid and solid crystal phases, in which small grains of close-packed crystal coexisted with the fluid.

Three diblock copolymers of propylene oxide and ethylene oxide were prepared by sequential oxyanionic polymerization; P94E316, P60E348, and P43E312. Light scattering and dye solubilization were used to confirm micellization in dilute aqueous solution and to determine the temperature dependence of the critical micelle concentration (cmc), and eluent gel permeation chromatography was used to determine the extent of micellization. Comparison with results for the series of copolymers EmPn (m = 98-104, n = 37-73, published previously) shows that values of the cmc in molar units depend almost entirely on P-block length, i.e., that the effect of E-block length on critical micelle concentration is insignificant in the range m = 100-300. Light scattering was also used to determine micellar association numbers (NW) and radii. Present and previous values of NW fit well to a scaling law for block lengths (P and E) similar to that proposed by Nagarajan and Ganesh for EmPn copolymers. Gel boundaries were determined by a tube-inversion method, and critical gel concentrations were found to coincide with values predicted by using micellar parameters determined by static light scattering.

Four EBE copolymers (E = oxyethylene repeat unit, B = oxybutylene repeat unit) based on a B20 central block and end blocks ranging from 58 to 260 E units were studied. Rheological measurements (oscillatory and steady shear) were used to confirm gel boundaries (previously explored by a tube inversion method) and to determine storage and loss moduli (G′ and G″) and yield stresses (σy) for aqueous gels formed at copolymer concentrations below 20 wt %. The phase diagrams contained a region of hard gel (G′ > G″, high G′ and σy), an extensive region of soft gel ((G′ > G″, low G′ and σy), denoted 1, and a second region of soft gel at low temperatures, denoted 2. Small-angle X-ray scattering was used to probe the hard gel structure. Concentrated aqueous gels (20 wt %) had a body-centered cubic (bcc, Im3̄m) structure. The structure of dilute gels near to the hard gel boundary was not defined, although the Im3̄m and Pm3̄n cubic structures were eliminated. Depending on concentration, the soft gels were assigned either to percolation-induced fractal structures (soft gel 1) or to defective cubic structures (soft gels 1 and 2).