To date, over 20 peptides or proteins have been identified that can form amyloid fibrils in the body and are thought to cause disease. The mechanism by which amyloid peptides cause the cytotoxicity ...observed and disease is not understood. However, one of the major hypotheses is that amyloid peptides cause membrane perturbation. Hence, we have studied the interaction between lipid bilayers and the 37 amino acid residue polypeptide amylin, which is the primary constituent of the pancreatic amyloid associated with type 2 diabetes. Using a dye release assay we confirmed that the amyloidogenic human amylin peptide causes membrane disruption; however, time-lapse atomic force microscopy revealed that this did not occur by the formation of defined pores. On the contrary, the peptide induced the formation of small defects spreading over the lipid surface. We also found that rat amylin, which has 84% identity with human amylin but cannot form amyloid fibrils, could also induce similar lesions to supported lipid bilayers. The effect, however, for rat amylin but not human amylin, was inhibited under high ionic conditions. These data provide an alternative theory to pore formation, and how amyloid peptides may cause membrane disruption and possibly cytotoxicity.
Despite considerable interest and investigations on cationic lipid–DNA complexes, reports on lipid–RNA interaction are very limited. In contrast to lipid–DNA complexes where lipid binding induces ...partial B to A and B to C conformational changes, lipid–tRNA complexation preserves tRNA folded state. This study is the first attempt to investigate the binding of cationic lipid with transfer RNA and the effect of lipid complexation on tRNA aggregation and condensation. We examine the interaction of tRNA with cholesterol (Chol), 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), dioctadecyldimethylammoniumbromide (DDAB) and dioleoylphosphatidylethanolamine (DOPE), at physiological condition, using constant tRNA concentration and various lipid contents. FTIR, UV-visible, CD spectroscopic methods and atomic force microscopy (AFM) were used to analyze lipid binding site, the binding constant and the effects of lipid interaction on tRNA stability, conformation and condensation. Structural analysis showed lipid–tRNA interactions with G–C and A–U base pairs as well as the backbone phosphate group with overall binding constants of KChol = 5.94 (± 0.8) × 104 M–1, KDDAB = 8.33 (± 0.90) × 105 M–1, KDOTAP = 1.05 (± 0.30) × 105 M–1 and KDOPE = 2.75 (± 0.50) × 104 M–1. The order of stability of lipid–tRNA complexation is DDAB > DOTAP > Chol > DOPE. Hydrophobic interactions between lipid aliphatic tails and tRNA were observed. RNA remains in A-family structure, while biopolymer aggregation and condensation occurred at high lipid concentrations.
Poly(ethylene glycol) (PEG) and its derivatives are synthetic polymers with major applications in gene and drug delivery systems. Synthetic polymers are also used to transport miRNA and siRNA in ...vitro. We studied the interaction of tRNA with several PEGs of different compositions, such as PEG 3350, PEG 6000, and mPEG-anthracene under physiological conditions. FTIR, UV–visible, CD, and fluorescence spectroscopic methods as well as atomic force microscopy (AFM) were used to analyze the PEG binding mode, the binding constant, and the effects of polymer complexation on tRNA stability, aggregation, and particle formation. Structural analysis showed that PEG-tRNA interaction occurs via RNA bases and the backbone phosphate group with both hydrophilic and hydrophobic contacts. The overall binding constants of K PEG 3350‑tRNA= 1.9 (±0.5) × 104 M–1, K PEG 6000‑tRNA = 8.9 (±1) × 104 M–1, and K mPEG‑anthracene= 1.2 (±0.40) × 103 M–1 show stronger polymer–RNA complexation by PEG 6000 and by PEG 3350 than the mPEG-anthracene. AFM imaging showed that PEG complexes contain on average one tRNA with PEG 3350, five tRNA with PEG 6000, and ten tRNA molecules with mPEG-anthracene. tRNA aggregation and particle formation occurred at high polymer concentrations, whereas it remains in A-family structure.
Self-assembled monolayers are widely used to modify the gate dielectric/semiconductor interface in organic thin-film transistors. By modifying the interaction between the molecular semiconductor and ...the substrate, thin-film ordering and the electronic properties of the semiconducting channel can be controlled. The modified semiconductor/dielectric properties result in macroscopically observed changes in the charge-carrier mobilities, threshold voltages, subthreshold swing and transfer characteristic hysteresis. The latter two are determined by the density of charge-trapping states at the interface. Here, we investigate the influence of the thickness of the self-assembled monolayer, via the alkyl chain length in n-alkyl phosphonic acid-based monolayers on SiO
2
, on the electronic properties of pentacene-based organic thin-film transistors. Rather than a monotonic increase or decrease in performance with increasing chain length, we have found that the optimum performance occurs with chains of 8–10 carbon atoms. Atomic force microscopy shows a correlation between pentacene crystalline grain size and transistor performance.
Structure of MnSi on SiC(0001) Meynell, S. A.; Spitzig, A.; Edwards, B. ...
Physical review. B,
11/2016, Letnik:
94, Številka:
18
Journal Article
Recenzirano
We report on the growth and magnetoresistance of MnSi films grown on SiC(0001) by molecular beam epitaxy. The growth resulted in a textured MnSi(111) film with a predominantly 11¯0MnSi(111)∥112¯0 ...SiC(0001) epitaxial relationship, as demonstrated by transmission electron microscopy, reflection high energy electron diffraction, and atomic force microscopy. The 500 ∘C temperature required to crystallize the film leads to a dewetting of the MnSi layer. Although the sign of the lattice mismatch suggested the films would be under compressive stress, the films acquire an in-plane tensile strain likely driven by the difference in thermal expansion coefficients between the film and substrate during annealing. As a result, the magnetoresistive response demonstrates that the films possess a hard-axis out-of-plane magnetocrystalline anisotropy.
The mechanical behavior of human hair fibers is determined by the interactions between keratin proteins structured into microfibrils (hard
α-keratin intermediate filaments), a protein sulfur-rich ...matrix (intermediate filaments associated proteins), and water molecules. The structure of the microfibril-matrix assembly has already been fully characterized using electron microscopy and small-angle x-ray scattering on unstressed fibers. However, these results give only a static image of this assembly. To observe and characterize the deformation of the microfibrils and of the matrix, we have carried out time-resolved small-angle x-ray microdiffraction experiments on human hair fibers stretched at 45% relative humidity and in water. Three structural parameters were monitored and quantified: the 6.7-nm meridian arc, which is related to an axial separation between groups of molecules along the microfibrils, the microfibril’s radius, and the packing distance between microfibrils. Using a surface lattice model of the microfibril, we have described its deformation as a combination of a sliding process and a molecular stretching process. The radial contraction of the matrix is also emphasized, reinforcing the hydrophilic gel nature hypothesis.
Morphologically, glutaraldehyde-fixed and -dried intermediate filaments (IFs) appear flexible, and with a width of 8–12
nm when observed by electron microscopy. Sometimes, the filaments are even ...unraveled on the carbon-coated grid and reveal a protofilamentous architecture. In this study, we have used atomic force microscopy to further investigate the morphology of IFs in a more physiological environment. First, we have imaged hydrated glutaraldehyde-fixed IFs adsorbed to a graphite support. In such conditions, human vimentin and desmin IFs appeared compact with a height of 5–8
nm and revealed either a beading repeat or a helical morphology. Second, we have analyzed the architecture of hydrated vimentin, desmin, and neurofilament IFs adsorbed to mica, graphite, and hydrophilic glass without the presence of fixative. On mica, vimentin IFs had a height of only 3–5
nm, whereas desmin IFs appeared as 8–10
nm height filaments with a helical twist. Neurofilaments were 10–12
nm in height with a pronounced 30–50
nm beading along their length. On graphite, the different IFs were either not adsorbing properly or their architecture was modified yielding, for example, broad, flattened filaments. Finally, hydrophilic glass was the surface which seemed to best preserve the architecture of the three IFs, even if, in some cases, unraveled vimentin filaments were observed on this support. These results are straightening the idea that mature IFs are dynamic polymers in vitro and that IFs can be distinguished from each others by their physicochemical properties.
PDF
