A FRET Probe for Cell‐Based Imaging of Ganglioside‐Processing Enzyme Activity and High‐Throughput Screening

Gangliosides are important signaling molecules in the cell membrane and are processed by several enzymes. Deficiencies in these enzymes can cause human lysosomal storage diseases. Building an understanding of the pathways of glycosphingolipid catabolism requires methods for the analysis of these enzymatic activities A GM3‐derived FRET probe was synthesized chemoenzymatically for the detection and quantitation of a range of ganglioside‐degrading enzymes, both in cell lysates and in living cells. This is the first substrate that enables the ratiometric fluorogenic assay of sphingolipid ceramide N‐deacylase and endoglycoceramidase and can detect and localize neuraminidase activity in living cells. It is therefore a valuable tool for building a better understanding of membrane‐confined enzymology. It also enables the robust and reliable assay of ganglioside‐degrading enzymes in a microtiter plate, thus opening the door to screening for novel or engineered biocatalysts or for new inhibitors.     

One step closer to a sweet conclusion

OtsA is required for the biosynthesis of trehalose, a nonreducing disaccharide that is important for bacterial survival and stress responses. In this issue of Chemistry & Biology, the structure of OtsA is uncovered and reveals an unexpected relationship between the enzyme's structure and function.     

Temperature-dependent electrical, elastic and magnetic properties of sol-gel synthesized Bi(0.9)Ln(0.1)FeO3 (Ln = Nd, Sm)

This report details correlated electrical, mechanical and magnetic behaviour in BiFeO(3) ceramics doped with 10% Ln (Ln = Sm, Nd) ions on the Bi, or perovskite A, site and synthesized by a sol-gel method. The ceramics exhibit bulk piezoelectric and ferroelectric properties and clear ferroelectric domain patterns through piezoresponse force microscopy. Resonant ultrasound spectroscopy, dielectric spectroscopy and magnetometry studies show correlated magnetoelectromechanical behaviour and the existence of weak ferromagnetism for both compositions. An anomaly with simultaneous mechanical and magnetic signatures is discovered in both materials near room temperature, while previously reported transitions and anomalies are found to exhibit electro- and/or magnetomechanical coupling. Magnetism is significantly enhanced in the Sm doped sample, which is a promising multiferroic material.     

Synthesis, structures and phase transitions in the double perovskites Sr2−xCaxCrNbO6

The synthesis and crystal structures of nine members of the rock-salt ordered double perovskites Sr_2−xCa_xCrNbO₆ is presented. The crystal structures of the end members of the series Sr₂CrNbO₆ and Ca₂CrNbO₆ were refined using powder neutron diffraction data and are cubic in and monoclinic in P2₁/n, respectively, in both cases there being considerable anti-site Cr-Nb mixing. Variable temperature and/or composition studies suggest a direct first-order P2₁/n to transition, a suggestion supported by selected area electron diffraction studies.     

A priori information in a regularized sinogram‐based method for removing ring artefacts in tomography

Ring artefacts in X‐ray computerized tomography reconstructions are considered. The authors propose a ring artefact removal method based on a priori information regarding the sinogram including smoothness along the horizontal coordinate, symmetry of the first and the final rows and consideration of small perturbations during acquisition. The method does not require prior reconstruction of the original or corrected sinograms. Its numerical implementation is based on quadratic programming. Its efficacy is examined with regard to experimental data sets collected on graphite and bone.     

Isolation of sterols with cyclopropyl-containing side chains from the cultured marine alga peridiniumfoliaceum

The sterol fraction of the cultured dinoflagellate $\text{Peridinium}$$\text{foliaceum}$ contains in addition to cholesterol, 24-methylcholesterol, 4,24-dimethylcholesterol and dinosterol ($\text{3c}$) small amounts of the cyclopropyl-containing sterols gorgosterol ($\text{1a}$) and 5α-gorgostanol ($\text{1b}$) as well as 4α-methylgorgostanol ($\text{1c}$) and E-4α,22ξ,23ξ (or 24ξ)-trimethylcholest-17(20)-en-3β-ol ($\text{6c}$ or $\text{7c}$). The biosynthetic implications of the first isolation of such sterols from a free-living alga are emphasized.     

High-Modulus Wholly Aromatic Fibers. II. Partially Ordered Polyamide-Hydrazides

Partially ordered polyarnide-hydrazides were produced by the poly condensation of diacid chlorides with aminobenz-hydrazides, the order that results being a consequence of the considerably more rapid reaction of a diacid chloride with the hydrazide group in competition with the aromatic amine group of the aminobenzhydrazide. Fibers were produced from a series of such polymers containing from 50 mole % meta-oriented phenylene rings to 100 mole % para-oriented ones. Fiber from the wholly para-oriented type of polymer exhibited very high strength and modulus: 12.5 and 468 g/den, respectively, at 4.3% elongation-to-break. Although the crystallinity and density observed for hot-drawn fibers of partially ordered completely para-oriented polyarnide-hydrazides were comparable to the crystallinity and density of fibers of the isomeric wholly ordered polymer, the partially ordered polymers were more readily spun to the ultra-high strength and high modulus type fibers, probably because their greater solubility made them easier to spin.     

High-Modulus Wholly Aromatic Fibers. I. Wholly Ordered Polyamide-Hydrazides and Poly-1,3,4-oxadiazole—Amides

Several completely ordered polyamide-hydrazide copolymers were prepared via low temperature poly condensation of aromatic diacid chlorides with symmetrical aromatic diamines containing preformed dihydrazide linkages. Highly crystalline, hot-drawn fibers of the polyamide-hydrazide containing only para-oriented phenylene units showed unusually high strength and exceptionally high initial modulus: 10.8 and 508 g/den, respectively, at 2.9% elongation-to-break. The as-spun fibers also exhibited rather high tensile strength and unusually high initial modulus: 8.2 and 291 g/den, respectively, at 9.4% elongation-to-break. The hot-drawn fiber retained considerable strength at elevated temperatures, exhibiting a tenacity of 1.4 g/den and an initial modulus of 169 g/den at 350°C. Heat-aging of the as-spun fiber at 185°C in air showed that 66% of the original tenacity, 41% of the elongation, and 86% of the modulus were retained even after 336 hr. Substitution of as little as 25 mole % meta-oriented phenylene rings for para-oriented ones resulted in loss of the ultra-high strength and modulus, giving tensile properties comparable to those of fibers from wholly aromatic polyamides of the meta-oriented type. Fibers from the polyamide-hydrazides containing 50 mole % meta-oriented rings showed similar properties. Although ordered oxadiazole-amide copolymers were obtained from diamines containing two preformed oxadiazole linkages separated by m-phenylene rings, fibers could not be spun from them. Fiber of an ordered oxadiazole-amide copolymer was obtained, however, by heat treatment of the wholly p-phenylene ordered poly amide-hydrazide copolymer precursor fiber. Such a fiber exhibited a tenacity of 15.3 g/den, 3.6% elongation-to-break, and 564 g/den initial modulus.     

Low-conductivity buffers for high-sensitivity NMR measurements

The sensitivity of nuclear magnetic resonance (NMR) probes, especially the recently introduced cryogenic probes, can be substantially reduced by the electrical noise generated by conductive samples. In particular, samples of biological macromolecules, which usually contain salts to keep the pH constant and to prevent aggregation, can experience a significant reduction in sensitivity. So far this dependence has forced researchers to minimize the salt concentrations in their samples. Here we demonstrate that the decisive factor is not the salt concentration itself but the conductivity which is a function of both the concentration and the mobility of the ions in solution. We show that by choosing buffers with low ionic mobility, the sample conductivity can be dramatically reduced and the sensitivity substantially enhanced compared to the same measurement with an equal concentration of a standard NMR buffer such as phosphate. We further show that the highest sensitivity gain of one buffer over another buffer is equal to the square root of the ratio of their ion mobilities and describe a simple method to evaluate the effect of a certain buffer on the sensitivity.     

Structure, crystal chemistry and thermal evolution of the δ-Bi2O3-related phase Bi9ReO17

The thermal evolution and structural properties of fluorite-related δ-Bi₂O₃-type Bi₉ReO₁₇ were studied with variable temperature neutron powder diffraction, synchrotron X-ray powder diffraction and electron diffraction. The thermodynamically stable room-temperature crystal structure is monoclinic P2₁/c, a=9.89917(5), b=19.70356(10), c=11.61597(6) Å, β=125.302(2)° (R_p=3.51%, wR_p=3.60%) and features clusters of ReO₄ tetrahedra embedded in a distorted Bi–O fluorite-like network. This phase is stable up to 725 °C whereupon it transforms to a disordered δ-Bi₂O₃-like phase, which was modeled with δ-Bi₂O₃ in cubic Fm3¯m with a=5.7809(1) Å (R_p=2.49%, wR_p=2.44%) at 750 °C. Quenching from above 725 °C leads to a different phase, the structure of which has not been solved but appears on the basis of spectroscopic evidence to contain both ReO₄ tetrahedra and ReO₆ octahedra.