Morphological and Structural Aspects of the Extremely Halophilic Archaeon Haloquadratum walsbyi

Ultrathin square cell Haloquadratum walsbyi from the Archaea domain are the most abundant microorganisms in the hypersaline water of coastal salterns and continental salt lakes. In this work, we explore the cell surface of these microorganisms using amplitude-modulation atomic-force microscopy in nearly physiological conditions. We demonstrate the presence of a regular corrugation with a periodicity of 16–20 nm attributed to the surface layer (S-layer) protein lattice, striped domains asymmetrically distributed on the cell faces and peculiar bulges correlated with the presence of intracellular granules. Besides, subsequent images of cell evolution during the drying process indicate the presence of an external capsule that might correspond to the giant protein halomucin, predicted by the genome but never before observed by other microscopy studies

Dosimeter based on silver-nanoparticle precursors for medical applications with linear response over a wide dynamic range

In this Letter the authors study a liquid detector based on Ag nanoparticles for dosimetry purposes. They use two different concentrations of silver nitrate (1 mM AgNO3) and sodium citrate (1 and 0.1% C6H5O7Na3) as precursors for the formation of Ag nanoparticles in an aqueous colloidal solution. The authors utilise a linear accelerator to expose the solutions to absorbed doses ranging from 0.5 to 120 Gy and they find that gamma radiation induces the synthesis of Ag nanoparticles already at 2 Gy, when the sodium citrate concentration is lowered to 0.1 . The authors find a correlation between shape/dimension of the Ag nanoparticles and the absorbed dose. More importantly, the authors show that the absorbance peak intensity of the Ag nanoparticles increases with the absorbed dose and that a linear dependence is achieved at the lower sodium citrate concentration

2007)Cardiolipin is associated with the terminal oxidase of an extremely halophilic archaeon

Abstract Membranes having an a high content of cardiolipin were isolated from an extremely halophilic archaeon Halorubrum sp. Absorbance difference spectra of detergent-solubilized plasma membranes reduced by dithionite suggested the presence of b-type cytochromes. Nondenaturing gel electrophoresis revealed only one fraction having TMPD-oxidase activity in which cardiolipin was the major lipid component. The electroeluted fraction showed a cytochrome c oxidase activity characterized by the reduced minus oxidized difference spectra as a terminal heme-copper oxidase. The cytochrome c oxidase activity of the archaeal cardiolipin-rich membranes was inhibited by the cardiolipin-specific fluorescent marker 10-N-nonyl acridine orange (NAO) in a dose-dependent manner. The results indicate that an archaeal analogue of cardiolipin is tightly associated to archaeal terminal oxidases and is required for its optimal functioning

Mitochondria isolated in nearly isotonic KCl buffer: focus on cardiolipin and organelle morphology

Rat liver mitochondria were isolated in parallel in two different isolation buffers: a standard buffer containing mannitol/sucrose and a nearly physiological KCl based solution. The two different organelle preparations were comparatively characterized by respiratory activity, heme content, microsomal and Golgi contamination, electron microscopy and lipid analyses. The substitution of saccharides with KCl in the isolation buffer does not induce the formation of mitoplasts or disruption of mitochondria. Mitochondria isolated in KCl buffer are coupled and able to maintain a stable transmembrane charge separation. A number of biochemical and functional differences between the two organelle preparations are described; in particular KCl mitochondria exhibit lower cardiolipin content and smaller intracristal compartments in comparison with the standard mitochondrial preparation

Aggregation of Aß(25-35) on DOPC and DOPC/DHA bilayers: an atomic force microscopy study

β amyloid peptide plays an important role in both the manifestation and progression of Alzheimer disease. It has a tendency to aggregate, forming low-molecular weight soluble oligomers, higher-molecular weight protofibrillar oligomers and insoluble fibrils. The relative importance of these single oligomeric-polymeric species, in relation to the morbidity of the disease, is currently being debated. Here we present an Atomic Force Microscopy (AFM) study of Aβ(25-35) aggregation on hydrophobic dioleoylphosphatidylcholine (DOPC) and DOPC/docosahexaenoic 22∶6 acid (DHA) lipid bilayers. Aβ(25-35) is the smallest fragment retaining the biological activity of the full-length peptide, whereas DOPC and DOPC/DHA lipid bilayers were selected as models of cell-membrane environments characterized by different fluidity. Our results provide evidence that in hydrophobic DOPC and DOPC/DHA lipid bilayers, Aβ(25-35) forms layered aggregates composed of mainly annular structures. The mutual interaction between annular structures and lipid surfaces end-results into a membrane solubilization. The presence of DHA as a membrane-fluidizing agent is essential to protect the membrane from damage caused by interactions with peptide aggregates; to reduces the bilayer defects where the delipidation process starts

New Aβ(1-42) ligands from anti-amyloid antibodies:Design, synthesis, and structural interaction

: Alzheimer's disease (AD), is the most common neurodegenerative disorder of the aging population resulting in progressive cognitive and functional decline. Accumulation of amyloid plaques around neuronal cells is considered a critical pathogenetic event and, in most cases, a hallmark of the pathology. In the attempt to identify anti-AD drug candidates, hundreds of molecules targeting Aβ peptides have been screened. Peptide molecules have been widely explored, appreciating chemical stability, biocompatibility, and low production cost. More recently, many anti-Aβ(1-42) monoclonal antibodies have been developed, given the excellent potential of immunotherapy for treating or preventing AD. Antibodies are versatile ligands that bind a large variety of molecules with high affinity and specificity; however, their extensive therapeutic application is complex and requires huge economic investments. Novel approaches to identify alternative antibody formats are considered with great interest. In this context, taking advantage of the favorable peptide properties and the availability of Aβ-antibodies structural data, we followed an innovative research approach to identify short peptide sequences on the model of the binding sites of Aβ(1-42)/antibodies. WAibH and SYSTPGK were designed as mimics of solanezumab and aducanumab, respectively. Circular dichroism and nuclear magnetic resonance analysis reveal that the antibody-derived peptides interact with Aβ(1-42) in the soluble monomeric form. Moreover, AFM microscopy imaging shows that WAibH and SYSTPGK are capable of controlling the Aβ(1-42) aggregation. The strategy to identify WAibH and SYSTPGK is innovative and can be widely applied for new anti-Aβ antibody mimicking peptides

DOPC and DOPC/DHA lipid bilayers.

<p>(a) Height AFM images of DOPC (2.5×2.5 µm² 1024×1024px²) and DOPC/DHA (b) (2.5×2.5 512×512px²) lipid bilayers performed in tapping mode and in PBS. The bilayers cover 92% (DOPC) and 96% (DOPC/DHA) of the mica surface. On DOPC lipid particles collected at the border or within defects are due to incomplete bilayer formation or to defective rinsing.</p

Aβ(25-35) aggregation on DOPC/DHA lipid bilayer.

<p>(a-c) 5×2.2 µm² (1024×431px²) topographic AFM images of Aβ(25-35) aggregation on DOPC/DHA lipid bilayers. (d) Graph showing the increasing surface area covered by LA (blue line) and the lipid bilayer evolution over time (red line). LA structures were grown within the first 30 min of peptide deposition while the lipid surface area decreased slowly from 96% to 91%. Data were qualitatively fitted by rational and sigmoidal functions for the DOPC/DHA bilayer (Θ_DOPC/DHA) and the LA domains (Θ_P), respectively. Fitting curves act as guide-to-the-eye. (e) Height distribution histograms measured at t = 0 min (black), 30 min (red), 1 h (green), 1 h45 min (blue), 2 h (cyan) and 2 h20 min (magenta).</p