Filamentous Nanostructures Research Articles

Construction of a Xylanase A Variant Capable of Polymerization

The aim of our work is to furnish enzymes with polymerization ability by creating fusion constructs with the polymerizable protein, flagellin, the main component of bacterial flagellar filaments. The D3 domain of flagellin, exposed on the surface of flagellar filaments, is formed by the hypervariable central portion of the polypeptide chain. D3 is not essential for filament formation. The concept in this project is to replace the D3 domain with suitable monomeric enzymes without adversely affecting polymerization ability, and to assemble these chimeric flagellins into tubular nanostructures. To test the feasibility of this approach, xylanase A (XynA) from B. subtilis was chosen as a model enzyme for insertion into the central part of flagellin. With the help of genetic engineering, a fusion construct was created in which the D3 domain was replaced by XynA. The flagellin-XynA chimera exhibited catalytic activity as well as polymerization ability. These results demonstrate that polymerization ability can be introduced into various proteins, and building blocks for rationally designed assembly of filamentous nanostructures can be created.

Switching of Self-Assembly in a Peptide Nanostructure with a Specific Enzyme.

Peptide self-assembly has been shown to be a useful tool for the preparation of bioactive nanostructures, and recent work has demonstrated their potential as therapies for regenerative medicine. In principle, one route to make these nanostructures more biomimetic would be to incorporate in their molecular design the capacity for biological sensing. We report here on the use of a reversible enzymatic trigger to control the assembly and disassembly of peptide amphiphile (PA) nanostructures. The PA used in these studies contained a consensus substrate sequence specific to protein kinase A (PKA), a biological enzyme important for intracellular signaling that has also been shown to be an extracellular cancer biomarker. Upon treatment with PKA, this PA molecule becomes phosphorylated causing the high aspect-ratio filamentous PA nanostructures to disassemble. Treatment with an enzyme to cleave the phosphate group results in reformation of the filamentous nanostructures. We also show that disassembly in the presence of PKA allows the enzyme-triggered release of an encapsulated cancer drug. In addition, these drug-loaded nanostructures were found to induce preferential cytotoxicity in a cancer cell line that is known to secrete high levels of PKA. This ability to control nanostructure through an enzymatic switch could allow for the preparation of highly sophisticated and biomimetic materials that incorporate a biological sensing capability to enable therapeutic specificity.

Self-assembled filamentous nanostructures for drug/gene delivery applications

Importance of the field: Among many nanostructural shapes, filamentous shapes can have unique advantages over the others, including longer persistence in the bloodstream. With the advent of nanotechnology in recent years, a variety of shape-controlled nanostructures has been fabricated. As a wide variety of building blocks can self-assemble into filamentous nanostructures, there are many options available for biomaterial developments with filamentous nanostructures. Similarly to conventional spherical micelles, most filamentous nanostructures have hydrophobic cores where hydrophobic guest molecules can be encapsulated, which enable them to be used in drug delivery applications. Moreover, on suitable molecular design and self-assembly process control, filamentous nanostructures can also be made to deliver nucleic acids or even both drugs and nucleic acids simultaneously.Areas covered in this review: This review describes the self-assembly process, current developments, and prospects of filamentous nanostructures in drug and gene delivery applications.What the reader will gain: This review should be helpful in gaining insight into the self-assembly process and nanostructural shape control, the advantages of constructing filamentous nanostructures, and the design of more advanced nanobiomaterials.Take home message: At present, the development of multifunctional nanostructures is one of the main focuses in nanobiomaterial developments. In this regard, filamentous nanostructures can be good initial targets for tailor-made nanostructure developments because they have more structural variables, as compared with spherical micelles.

Influence of a Fe/activated carbon catalyst and reaction parameters on methane decomposition during the synthesis of carbon nanotubes

AbstractIn our experimental work on carbon nanotubes synthesis, the influence of pre-treatment and reaction temperature conditions over Fe catalyst loaded on low-cost activated carbon (AC) in the catalytic chemical vapor deposition of methane was studied. Catalyst with the metal concentration of 5 mass % calcined at 350°C and reduced at 450°C was effective in CH4 decomposition giving 98 % conversions. TEM images showed that thin multi-walled carbon nanotubes (MWNTs) with the average internal diameter of ∼ 8 nm and the wall thickness of ∼ 2.5 nm were obtained over unreduced Fe/AC catalyst at the reaction temperature of 850°C. On the other hand, broader filamentous nanostructures with the diameter of ∼ 22 nm and the wall thickness of ∼ 3.72 nm were observed over reduced catalyst.

Quantitative approaches for characterising fibrillar protein nanostructures

AbstractPolypeptide sequences have an inherent tendency to self-assemble into filamentous nanostructures commonly known as amyloid fibrils. Such self-assembly is used in nature to generate a variety of functional materials ranging from protective coatings in bacteria to catalytic scaffolds in mammals. The aberrant self-assembly of misfolded peptides and proteins is also, however, implicated in a range of disease states including neurodegenerative conditions such as Alzheimer's and Parkinson's diseases. It is increasingly evident that the intrinsic material properties of these structures are crucial for understanding the thermodynamics and kinetics of the pathological deposition of proteins, particularly as the mechanical fragmentation of aggregates enhances the rate of protein deposition by exposing new fibril ends which can promote further growth. We discuss here recent advances in physical techniques that are able to characterise the hierarchical self-assembly of misfolded protein molecules and define their properties.

Optical determination of the flexural rigidity of carbon nanotube ensembles

We demonstrate two simple and consistent optical methods for quantitatively determining the flexural rigidity EI (where E is the elastic modulus and I the moment of inertia), a quantity of practical importance in determining the deflection and buckling characteristics of carbon nanotubes (CNTs). This is done through monitoring the deflection of patterned arrays of CNTs, which are subject to fluid flow. In addition to mechanical characterization of filamentous nanostructures, the implications of our work extend to the monitoring of nanoscale fluid flows for tactile and shear force sensors and the characterization of the mechanosensor response of cilia in physiology.

Manganese(IV) Oxide Production by Acremonium sp. Strain KR21-2 and Extracellular Mn(II) Oxidase Activity

Ascomycetes that can deposit Mn(III, IV) oxides are widespread in aquatic and soil environments, yet the mechanism(s) involved in Mn oxide deposition remains unclear. A Mn(II)-oxidizing ascomycete, Acremonium sp. strain KR21-2, produced a Mn oxide phase with filamentous nanostructures. X-ray absorption near-edge structure (XANES) spectroscopy showed that the Mn phase was primarily Mn(IV). We purified to homogeneity a laccase-like enzyme with Mn(II) oxidase activity from cultures of strain KR21-2. The purified enzyme oxidized Mn(II) to yield suspended Mn particles; XANES spectra indicated that Mn(II) had been converted to Mn(IV). The pH optimum for Mn(II) oxidation was 7.0, and the apparent half-saturation constant was 0.20 mM. The enzyme oxidized ABTS [2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)] (pH optimum, 5.5; Km, 1.2 mM) and contained two copper atoms per molecule. Moreover, the N-terminal amino acid sequence (residues 3 to 25) was 61% identical with the corresponding sequence of an Acremonium polyphenol oxidase and 57% identical with that of a Myrothecium bilirubin oxidase. These results provide the first evidence that a fungal multicopper oxidase can convert Mn(II) to Mn(IV) oxide. The present study reinforces the notion of the contribution of multicopper oxidase to microbially mediated precipitation of Mn oxides and suggests that Acremonium sp. strain KR21-2 is a good model for understanding the oxidation of Mn in diverse ascomycetes.

The effect of processing conditions on carbon nanostructures formed on an iron-based catalyst

The carbon nanostructures formed during chemical vapour deposition (CVD) of ethene and hydrogen over an iron(III) oxide catalyst precursor have been investigated. Graphitic nanofibres and carbon nanotubes were both observed during synthesis, with the structures observed depending on the temperature and gas mix (C 2H 4 and H 2) used. Mixtures ranging from 100% to 5% ethene in hydrogen were investigated at different temperatures. During the synthesis, the iron(III) oxide was transformed into iron carbide (Fe 3C). The samples were characterised using transmission electron microscopy and X-ray diffraction. Filamentous nanostructures were observed with high hydrogen content (⩾80%) in the gas stream, whereas no filamentous structures were observed with ⩽20% H 2. The temperature of synthesis was varied between 500 and 800 °C, with higher temperatures giving higher carbon deposition rates, but also affected the nanostructures observed. However, it was found that increasing the temperature during CVD did not change the type of carbon deposited but did increase the deposition rate, providing a route to increase growth yields for a desired type of carbon nanostructure.

High-sensitivity determination of birefringence in turbid media with enhanced polarization-sensitive optical coherence tomography

Polarization-sensitive optical coherence tomography provides high-resolution cross-sectional characterization of birefringence in turbid media. Weakly birefringent biological tissues such as the retinal nerve fiber layer (RNFL) require advanced speckle noise reduction for high-sensitivity measurement of form birefringence. We present a novel method for high-sensitivity birefringence quantification by using enhanced polarization-sensitive optical coherence tomography (EPS-OCT) and introduce the polarimetric signal-to-noise ratio, a mathematical tool for analyzing speckle noise in polarimetry. Multiple incident polarization states and non-linear fitting of normalized Stokes vectors allow determination of retardation with +/-1 degrees uncertainty with invariance to unknown unitary polarization transformations. Results from a weakly birefringent turbid film and in vivo primate RNFL are presented. In addition, we discuss the potential of EPS-OCT for noninvasive quantification of intracellular filamentous nanostructures, such as neurotubules in the RNFL that are lost during the progression of glaucoma.