Phase separation in the outer membrane of Escherichia coli.

Gram-negative bacteria are surrounded by a protective outer membrane (OM) with phospholipids in its inner leaflet and lipopolysaccharides (LPS) in its outer leaflet. The OM is also populated with many ß-barrel outer-membrane proteins (OMPs), some of which have been shown to cluster into supramolecular assemblies. However, it remains unknown how abundant OMPs are organized across the entire bacterial surface and how this relates to the lipids in the membrane. Here, we reveal how the OM is organized from molecular to cellular length scales, using atomic force microscopy to visualize the OM of live bacteria, including engineered Escherichia coli strains and complemented by specific labeling of abundant OMPs. We find that a predominant OMP in the E. coli OM, the porin OmpF, forms a near-static network across the surface, which is interspersed with barren patches of LPS that grow and merge with other patches during cell elongation. Embedded within the porin network is OmpA, which forms noncovalent interactions to the underlying cell wall. When the OM is destabilized by mislocalization of phospholipids to the outer leaflet, a new phase appears, correlating with bacterial sensitivity to harsh environments. We conclude that the OM is a mosaic of phase-separated LPS-rich and OMP-rich regions, the maintenance of which is essential to the integrity of the membrane and hence to the lifestyle of a gram-negative bacterium.

Resolving protein mixtures using microfluidic diffusional sizing combined with synchrotron radiation circular dichroism.

Circular dichroism spectroscopy has become a powerful tool to characterise proteins and other biomolecules. For heterogeneous samples such as those present for interacting proteins, typically only average spectroscopic features can be resolved. Here we overcome this limitation by using free-flow microfluidic size separation in-line with synchrotron radiation circular dichroism to resolve the secondary structure of each component of a model protein mixture containing monomers and fibrils. To enable this objective, we have integrated far-UV compatible measurement chambers into PDMS-based microfluidic devices. Two architectures are proposed so as to accommodate for a wide range of concentrations. The approach, which can be used in combination with other bulk measurement techniques, paves the way to the study of complex mixtures such as the ones associated with protein misfolding and aggregation diseases including Alzheimer's and Parkinson's diseases.

Rapid Growth of Acetylated Aß(16-20) into Macroscopic Crystals.

Aberrant assembly of the amyloid-ß (Aß) is responsible for the development of Alzheimer's disease, but can also be exploited to obtain highly functional biomaterials. The short Aß fragment, KLVFF (Aß16-20), is crucial for Aß assembly and considered to be an Aß aggregation inhibitor. Here, we show that acetylation of KLVFF turns it into an extremely fast self-assembling molecule, reaching macroscopic ( i.e., mm) size in seconds. We show that KLVFF is metastable and that the self-assembly can be directed toward a crystalline or fibrillar phase simply through chemical modification, via acetylation or amidation of the peptide. Amidated KLVFF can form amyloid fibrils; we observed folding events of such fibrils occurring in as little as 60 ms. The ability of single KLVFF molecules to rapidly assemble as highly ordered macroscopic structures makes it a promising candidate for applications as a rapid-forming templating material.

Nanostructural Differentiation and Toxicity of Amyloid-ß25-35 Aggregates Ensue from Distinct Secondary Conformation.

Amyloid nanostructures are originated from protein misfolding and aberrant aggregation, which is associated with the pathogenesis of many types of degenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease. The secondary conformation of peptides is of a fundamental importance for aggregation and toxicity of amyloid peptides. In this work, Aß25-35, a fragment of amyloid ß(1-42) (Aß42), was selected to investigate the correlation between secondary structures and toxicity of amyloid fibrils. Furthermore, each aggregation assemblies show different cell membrane disruption and cytotoxicity. The structural analysis of amyloid aggregates originated from different secondary structure motifs is helpful to understand the mechanism of peptides/cell interactions in the pathogenesis of amyloid diseases.

Thermal effect on the degradation of hIAPP20-29 fibrils.

Uncontrolled misfolding of proteins resulting in the formation of amyloid deposits is associated with over 40 types of diseases, for instance, type-2 diabetes. The human Islet amyloid polypeptide (hIAPP) amyloid formation is thought to be the cause of type-2 diabetes occurrence. A possible strategy to the current challenge of reducing the toxicity of its aggregates to pancreatic ß-cell is the discovery of an efficient way to degrading amyloid deposits. In this work, hIAPP20-29, a core fibrillating fragment of hIAPP, was selected as model system to explore the thermal effect at different temperature on the degradation of hIAPP20-29 mature fibrils. Insights on the degradation mechanism are obtained by analyzing the morphologies, the mechanical properties, the interactions between the peptides, and the secondary structure of amyloid aggregates. In addition, thermal degradation displayed a possible way to breaking the interaction of peptides and further disassembling the amyloid fibrils. These findings may initiate a new avenue to degrade the amyloid peptide aggregates and enrich and update the current selection of nanostructure modulations.

Light-driven porphyrin modulating fibrillation of hIAPP(20-29) peptide.

The human Islet amyloid polypeptide (20-29) (hIAPP20-29) is considered to be the core fibrillating fragment of hIAPP, which is associated with the pathogenesis of Type-II diabetes mellitus. A current challenge is the discovery of an efficient way to modulate amyloid aggregation and inhibit the toxicity of its aggregates. In this work, photoexcited porphyrins are successfully used to inhibit the fibrillation of hIAPP20-29. Insights on the inhibitory mechanism are explored by the analysis of the secondary structure, the morphology and the mechanical properties of amyloid aggregates. In addition, photoexcited porphyrins displayed a retained inhibitory effect on hIAPP20-29 aggregation without irradiation. These findings may establish a new avenue to inhibit the aggregation of amyloid peptide hIAPP and enrich the current selection of modulators.

A self-assembled nanopatch with peptide-organic multilayers and mechanical properties.

Peptides enable the construction of a diversity of one-dimensional (1D) and zero-dimensional (0D) nanostructures by molecular self-assembly. To date, it is a great challenge to construct two-dimensional (2D) nanostructures from peptides. Here we introduce an organic molecule to tune the amphiphilic-like peptide assembly to form a peptide-organic 2D nanopatch structure. The nanomechanical properties of the nanopatch were explored by quantitative nanomechanical imaging and force control manipulation. The peptide-organic patches are multilayers composed of several domains, which can be peeled off stepwise. The patch formation provides an approach towards constructing 2D nanostructures by peptide-organic assembly and it could be potentially utilized in a wide range of applications such as functional biomaterials.

Nanoliposomes containing Eucalyptus citriodora as antibiotic with specific antimicrobial activity.

Bacterial infections are a serious issue for public health and represent one of the major challenges of modern medicine. In this work, a selective antimicrobial strategy based on triggering of pore-forming toxin, which is secreted by infective bacteria, was designed to fight Staphylococcus aureus. The antimicrobial activity is realized by employing Eucalyptus citriodora oil as antibiotic which in this study is encapsulated in nanoliposomes.

The position of hydrophobic residues tunes peptide self-assembly.

The final structure and properties of synthetic peptides mainly depend on their sequence composition and experimental conditions. This work demonstrates that a variation in the positions of hydrophobic residues within a peptide sequence can tune the self-assembly. Techniques employed are atomic force microscopy, transmission electron microscopy and an innovative method based on surface acoustic waves. In addition, a systematic investigation on pH dependence was carried out by utilizing constant experimental parameters.

Ag-CuFe2O4 magnetic hollow fibers for recyclable antibacterial materials.

Copper ferrite (CuFe2O4) magnetic hollow fibers were prepared by applying an organic sol-thermal decomposition method, and silver nanoparticles were subsequently loaded on the fibers by calcination. The Ag-CuFe2O4 fibers exhibited excellent antibacterial efficacy against four different bacteria (E. coli, S. typhi, S. aureus and V. parahaemolyticus) with consistent results. Typical ferromagnetism behavior exhibited from the Ag-CuFe2O4 fibers enables their feasible recyclability.