[Show abstract][Hide abstract] ABSTRACT: The self-assembly of the Macrophage-Activating Lipopeptide MALP-2 in aqueous solution has been investigated and is compared to that of the constituent peptide GNNDESNISFKEK. MALP-2 is a Toll-like receptor agonist lipopeptide with diverse potential biomedical applications and its self-assembly has not previously been examined. It is found to self-assemble, above a critical aggregation concentration (cac), into remarkable "fibre raft" structures, based on lateral aggregation of β-sheet based bilayer tapes. Peptide GNNDESNISFKEK also forms β-sheet structures above a cac although the morphology is distinct, comprising highly extended and twisted tape structures. A detailed insight into the molecular packing within the MALP-2 raft and GNNDESNISFKEK nanotape structures is obtained through X-ray diffraction and small-angle X-ray scattering. These results point to the significant influence of the attached lipid chains on the self-assembly motif, which lead to the raft structure for the lipopeptide assemblies.
[Show abstract][Hide abstract] ABSTRACT: A conceptual design for artificial antimicrobial viruses is described. The design emulates viral assembly and function to create self-assembling peptide capsules that promote efficient gene delivery and silencing in mammalian cells. Unlike viruses, however, the capsules are antimicrobial, which allows them to exhibit a dual biological function: gene transport and antimicrobial activity. Unlike other antimicrobials, the capsules act as pre-concentrated antimicrobial agents that elicit rapid and localised membrane-disrupting responses by converting into individual pores at their precise landing positions on membranes. The concept holds promise for engineering virus-like scaffolds with biologically tuneable properties.
[Show abstract][Hide abstract] ABSTRACT: Protein self-assembled materials find increasing use in medicine and nanotechnology. A challenge remains in our ability to tailor such materials at a given length scale. Here we report a de novo self-assembly topology which enables the engineering of filamentous protein nanostructures under morphological control. The rationale is exemplified by a ubiquitous self-assembly motif - an α-helical coiled-coil stagger. The stagger incorporates regularly spaced interfacial tryptophan residues, which allows it to zipper up into discrete filaments that bundle together without thickening by maturation. Using a combination of spectroscopy, microscopy, X-ray small-angle scattering and fibre diffraction methods we show that the precise positioning of tryptophan residues at the primary and secondary structure levels defines the extent of coiled-coil packing in resultant filaments. Applicable to other self-assembling systems, the rationale holds promise for the construction of advanced protein-based architectures and materials.
No preview · Article · Oct 2015 · Physical Chemistry Chemical Physics
[Show abstract][Hide abstract] ABSTRACT: The amphiphilic polyene amphotericin B, a powerful treatment for systemic fungal infections, is shown to exhibit a critical aggregation concentration, and to form giant helically-twisted nanostructures via self-assembly in basic aqueous solution.
Full-text · Article · Oct 2015 · Chemical Communications
[Show abstract][Hide abstract] ABSTRACT: The spontaneous assembly of a peptide bolaamphiphile in water, namely RFL4FR (R: arginine, F: phenylalanine, L: leucine) is investigated, along with its novel properties in surface modification and usage as substrates for cell culture. RFL4FR self-assembles into nanosheets through lateral association of the peptide backbone. The L4 sequence is located within the core of the nanosheets while the R moieties are exposed to the water at the surface of the nanosheets. Kinetic assays indicate that the self-assembly is driven by a remarkable two-step process, where a nucleation phase is followed by fast growth of nanosheets with an autocatalysis process. The internal structure of the nanosheets is formed from ultra-thin bolaamphiphile monolayers with a crystalline orthorhombic symmetry with cross-β organization. We show that human corneal stromal fibroblast (hCSF) cells can grow on polystyrene films coated with films dried from RFL4FR solutions. For the first time this type of amphiphilic peptide is used as a substrate to modulate the wettability of solid surfaces for cell culture applications.
[Show abstract][Hide abstract] ABSTRACT: The self-assembly of peptide-nanotubes formed by an L-glutamic acid-based bolaamphiphile is shown to proceed via a remarkable mechanism where the peptide conformation changes from [small beta]-sheet to unordered. The kinetics of this process are elucidated via X-ray scattering and UV circular dichroism methods. The reverse transition from unordered to [small beta]-sheet structures is triggered by UV radiation.
Full-text · Article · Jun 2015 · Chemical Communications
[Show abstract][Hide abstract] ABSTRACT: Insight is provided into the thermodynamics and kinetics of peptide fibrillization, a process of particular interest in biomedicine due to its direct relationship to amyloid diseases. The studied isomeric tetrapeptides are terminally end-capped and present two hydrophobic phenylalanine residues and two ionizable hydrophilic aspartic acid residues. These compounds afford gels in water which are composed of self-assembled fibrillar networks. Potentiometric titrations have afforded acid-base and solubility constants associated to the fibrillization process. A remarkable pKa shift of the peptide side chains is observed linked to aggregation, affording fibers at pH values around neutrality. The magnitude of the pKa shift is directly related to the solubility of the tetrapeptides namely, to the free energy change associated with fibrillization. Therefore potentiometric titration emerges as a simple tool to evaluate the thermodynamic parameters of the process. Additionally kinetic measurements with NMR, fluorescence spectroscopy and SANS reveal that initial peptide dimerization is most likely to be the fibrillization rate determining step. The aggregation process in all cases presents a relatively long lag time of ca. 1-3 hours and takes more than 8 hours to complete. No correlation is observed between kinetic and thermodynamic parameters. Finally, kinetically controlled self-sorting of a mixture of two isomeric tetrapeptides is described
Full-text · Article · Apr 2015 · Chemistry of Materials
[Show abstract][Hide abstract] ABSTRACT: The self-assembly and bioactivity of a peptide amphiphile (PA) incorporating a 13-residue sequence derived from the last 13 amino acids of the C-terminus of lumican, C16- YEALRVANEVTLN, attached to a hexadecyl (C16) lipid chain have been examined. Lumican is a proteoglycan found in many types of tissue, and is involved in collagen fibril organization. A critical aggregation concentration (cac) for the PA was determined through pyrene fluorescence measurements. The structure of the aggregates was imaged using electron microscopy and twisted and curved nanotapes were observed. In situ small-angle X-ray scattering, and fibre X-ray diffraction, reveal that these tapes contain interdigitated bilayers of the PA molecules. FTIR and circular dichroism spectroscopies and fibre X-ray diffraction indicate that the lumican sequence in the PA adopts a β-sheet secondary structure. Cell assays using human dermal fibroblasts show that, below the cac, the PA displays good biocompatibility and also stimulated collagen production over a period of three weeks, exceeding a two-fold enhancement for several concentrations. Thus this PA has promise in future biological applications, in particular in tissue engineering.
[Show abstract][Hide abstract] ABSTRACT: A model octapeptide peptide consisting of an alternating sequence of arginine (Arg) and phenylalanine (Phe) residues, namely [Arg-Phe]4 was prepared, and its self-assembly in solution solution. The simple alternating [Arg-Phe]4 peptide sequence allows for unique insights into the aggregation process and the structure of the self-assembled motifs. Fluorescence and UV-Vis assays were used to determine critical aggregation concentrations, corresponding to the formation of oligomeric species and -sheet rich structures organized into both spheroidal aggregates and highly-ordered fibrils. Electron and atomic force microscopy images show globular aggregates and long unbranched fibres with diameters ranging from ~ 4 nm up to ~ 40 nm. Infrared and circular dichroism spectroscopy show the formation of β-sheet structures. X-ray diffraction on oriented stalks show that the peptide fibres have an internal lamellar structure, with an orthorhombic unit cell with parameters a ~ 27.6 Å, b ~ 9.7 Å and c ~ 9.6 Å. In situ small-angle X-ray scattering (SAXS) shows the presence of low molecular weight oligomers in equilibrium with mature fibres which are likely made up from 5 or 6 intertwined proto-filaments. Finally, weak gel solutions are probed under gentle shear suggesting the ability of these arginine-rich fibres to form networks.
[Show abstract][Hide abstract] ABSTRACT: We describe a bioactive lipopeptide that combines the capacity to promote the adhesion and subsequent self-detachment of live cells, using template-cell-environment feedback interactions. This self-assembling peptide amphiphile comprises a diene-containing hexadecyl lipid chain (C16e) linked to a matrix metalloprotease-cleavable sequence, Thr-Pro-Gly-Pro-Gln-Gly-Ile-Ala-Gly-Gln, and contiguous with a cell-attachment and signalling motif, Arg-Gly-Asp-Ser. Biophysical characterisation revealed that the PA self-assembles into 3 nm diameter spherical micelles above a critical aggregation concentration (cac). In addition, when used in solution at 5-150 nM (well below the cac), the PA is capable of forming film coatings that provide a stable surface for human corneal fibroblasts to attach and grow. Furthermore, these coatings were demonstrated to be sensitive to metalloproteases expressed endogenously by the attached cells, and consequently to elicit the controlled detachment of cells without compromising their viability. As such, this material constitutes a novel class of multi-functional coating for both fundamental and clinical applications.