Deamidation accelerates amyloid formation and alters amylin fiber structure

Deamidation of asparagine and glutamine is the most common nonenzymatic, post-translational modification. Deamidation can influence the structure, stability, folding, and aggregation of proteins and has been proposed to play a role in amyloid formation. However there are no structural studies of the consequences of deamidation on amyloid fibers, in large part because of the difficulty of studying these materials using conventional methods. Here we examine the effects of deamidation on the kinetics of amyloid formation by amylin, the causative agent of type 2 diabetes. We find that deamidation accelerates amyloid formation and the deamidated material is able to seed amyloid formation by unmodified amylin. Using site-specific isotope labeling and two-dimensional infrared (2D IR) spectroscopy, we show that fibers formed by samples that contain deamidated polypeptide contain reduced amounts of β-sheet. Deamidation leads to disruption of the N-terminal β-sheet between Ala-8 and Ala-13, but β-sheet is still retained near Leu-16. The C-terminal sheet is disrupted near Leu-27. Analysis of potential sites of deamidation together with structural models of amylin fibers reveals that deamidation in the N-terminal β-sheet region may be the cause for the disruption of the fiber structure at both the N- and C-terminal β-sheet. Thus, deamidation is a post-translational modification that creates fibers that have an altered structure but can still act as a template for amylin aggregation. Deamidation is very difficult to detect with standard methods used to follow amyloid formation, but isotope-labeled IR spectroscopy provides a means for monitoring sample degradation and investigating the structural consequences of deamidation.     

Sulfonato-encapsulated bismuth(III) oxido-clusters from Bi2O3 in water under mild conditions

Treatment of Bi(2)O(3) with the acids; S-(+)-10-camphorsulfonic, 2,4,6-mesitylenesulfonic and sulfamic, under sonication at room temperature in water for 2-4 h, results in the formation and subsequent crystallisation of polynuclear bismuth oxido-clusters; [Bi(18)O(12)(OH)(12)(O(3)S-Cam)(18)(H(2)O)(2)], [Bi(38)O(45)(O(3)S-Mes)(24)(H(2)O)(14)] and [Bi(6)O(4)(OH)(4)(O(3)SNH(2))(6)].     

A fluorescently labeled dendronized polymer-enzyme conjugate carrying multiple copies of two different types of active enzymes

A hybrid structure of a synthetic dendronized polymer, two different types of enzymes (superoxide dismutase and horseradish peroxidase), and a fluorescent dye (fluorescein) was synthesized. Thereby, a single polymer chain carried multiple copies of the two enzymes and the fluorescein. The entire attachment chemistry is based on UV/vis-quantifiable bis-aryl hydrazone bond formation that allows direct quantification of bound molecules: 60 superoxide dismutase, 120 horseradish peroxidase, and 20 fluorescein molecules on an average polymer chain of 2000 repeating units. To obtain other enzyme ratios the experimental conditions were altered accordingly. Moreover, it could be shown that both enzymes remained fully active and catalyzed a two-step cascade reaction.     

Cobalt(iii) complexes as functional ligands for metal (oxide) surfaces

Co(iii) polyamine complexes with either two or three labile coordination sites bind strongly to high surface area metal oxides such as goethite or aluminium trihydroxide, and have been shown to act as passivating agents for aluminium flake in aqueous media, in addition to providing a potential method for surface functionalisation.     

Post-assembly Functionalization of Organoplatinum(II) Metallacycles via Copper-free Click Chemistry

We describe the use of a strain-promoted copper-free click reaction in the post-self-assembly functionalization of organoplatinum(II) metallacycles. The coordination-driven self-assembly of a 120° cyclooctyne-tethered dipyridyl donor with 60° and 120° di-Pt(II) acceptors forms molecular rhomboids and hexagons bearing cyclooctynes. These species undergo post-self-assembly [3+2] Huisgen cycloaddition with a variety of azides to give functionalized ensembles under mild conditions.     

Euphohelioscopin A Is a PKC Activator Capable of Inducing Macrophage Differentiation

To identify small molecules that selectively control hematopoietic stem cell differentiation, we performed an unbiased screen using primary human CD34(+) cells. We identified a plant-derived natural product, euphohelioscopin A, capable of selectively differentiating CD34(+) cells down the granulocyte/monocytic lineage. Euphohelioscopin A also inhibits proliferation and induces differentiation of the myeloid leukemia cell lines THP-1 and HL-60. Mechanistic studies revealed that euphohelioscopin A is an activator of protein kinase C (PKC), and that the promonocytic effects of this natural product are mediated by PKC activation. In addition to shedding insights into normal hematopoiesis, this work may ultimately facilitate the application of stem cell therapies to a host of myeloid dysfunctions.     

M2 Proton Channel Structural Validation from Full-Length Protein Samples in Synthetic Bilayers and E. coli Membranes

Validation: Membrane protein structures are sensitive to the environment used for structural characterization. NMR spectra of the full-length M2 proton channel from influenza?A were measured directly in E.?coli membranes and compared to spectra of the protein in synthetic lipid bilayers. The results demonstrate that these bilayers provide a native-like membrane environment.     

Opportunities for innovation in neutron activation analysis

Neutron activation laboratories worldwide are at a turning point at which new staff has to be found for the retiring pioneers from the 1960s–1970s. A scientific career in a well-understood technique, often characterized as ‘mature’ may only be attractive to young scientists if still challenges for further improvement and inspiring new applications can be offered. The strengths and weaknesses of neutron activation analysis (NAA) are revisited to identify opportunities for innovation. Position-sensitive detection of elements in large samples, Monte Carlo calculations replacing the use of standards, use of scintillator detectors and new deconvolution techniques for increasing the sensitivity are examples of challenging new roads in NAA. Material science provides challenges for the application of NAA in both bulk samples, ultrathin layers and ultrapure materials.     

Virtual screening using a conformationally flexible target protein: models for ligand binding to p38α MAPK

We have used virtual screening to develop models for the binding of aryl substituted heterocycles to p38α MAPK. Virtual screening was conducted on a number of p38α MAPK crystal structures using a library of 46 known p38α MAPK inhibitors containing a heterocyclic core substituted by pyridine and fluorophenyl rings (structurally related to SB203580) and a set of decoy compounds. Multiple protonation states and tautomers of active and decoy compounds were considered. Each docking model was evaluated using receiver operating characteristic (ROC) curves and enrichment factors. The two best performing single crystal structures were found to be 1BL7 and 2EWA, with enrichment factors of 14.1 and 13.0 at 2 % of the virtual screen respectively. Ensembles of up to four receptors of similar conformations were generated, generally giving good or very good performances with high ROC AUCs and good enrichment. The 1BL7-2EWA ensemble was able to outperform each of its constituent receptors and gave high enrichment factors of 17.3, 12.0, 8.0 at 2, 5 and 10 % respectively, of the virtual screen. A ROC AUC of 0.94 was obtained for this ensemble. This method may be applied to other proteins where there are a large number of inhibitor classes with different binding site conformations.     

Crystal habit modifications of imatinib mesylate under various precipitation conditions

Abstract  

Crystals of the α-form of imatinib mesylate with various habits (e.g., polyhedral-like and plate-like) were prepared from various organic solvents (e.g., butyl lactate, 4-methyl-2-pentanone, 2-methyl-2-butanol, 2-isopropoxyethanol, propyl ether) by several precipitation methods. The methods provide imatinib mesylate in a non-needle-shaped crystalline α-form. The crystal modification was identified by hot-stage microscopy, scanning electron microscopy, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and X-ray powder diffraction (XRPD). The analyses by DSC, IR, and XRPD indicate that imatinib mesylate crystals with various habits have the same crystal structure. The plate-like habit has been also observed in the system where the organic solvent acts as a precipitant.