Neutron reflection from the liquid helium surface.

The reflection of neutrons from a helium surface has been observed for the first time. The 4He surface is smoother in the superfluid state at 1.54 K than in the case of the normal liquid at 2.3 K. In the superfluid state we also observe a surface layer ~200 Å thick which has a subtly different neutron scattering cross-section, which may be explained by an enhanced Bose-Einstein condensate fraction close to the helium surface. The application of neutron reflectometry described in this paper creates new and exciting opportunities for the surface and interfacial study of quantum fluids

Molecular interaction of the gamma-clade homeodomain-leucine zipper class I transcription factors during the wheat response to water deficit

The ᵧ-clade of class I homeodomain-leucine zipper (HD-Zip I) transcription factors (TFs) constitute members which play a role in adapting plant growth to conditions of water deficit. Given the importance of wheat (Triticum aestivum L.) as a global food crop and the impact of water deficit upon grain yield, we focused on functional aspects of wheat drought responsive HD-Zip I TFs. While the wheat ᵧ-clade HD-Zip I TFs share significant sequence similarities with homologous genes from other plants, the clade-specific features in transcriptional response to abiotic stress were detected. We demonstrate that wheat TaHDZipI- 3, TaHDZipI-4, and TaHDZipI-5 genes respond differentially to a variety of abiotic stresses, and that proteins encoded by these genes exhibit pronounced differences in oligomerisation, strength of DNA binding, and trans-activation of an artificial promoter. Three-dimensional molecular modelling of the protein-DNA interface was conducted to address the ambiguity at the central nucleotide in the pseudo-palindromic cis-element CAATNATTG that is recognised by all three HD-Zip I proteins. The coexpression of these genes in the same plant tissues together with the ability of HD-Zip I TFs of the ᵧ -clade to heterodimerise suggests a role in the regulatory mechanisms of HD-Zip I dependent transcription. Our findings highlight the complexity of TF networks involved in plant responses to water deficit. A better understanding of the molecular complexity at the protein level during crop responses to drought will enable adoption of efficient strategies for production of cereal plants with enhanced drought tolerance.John C. Harris, Pradeep Sornaraj, Mathew Taylor, Natalia Bazanova, Ute Baumann, Ben Lovell, Peter Langridge, Sergiy Lopato, Maria Hrmov

The impact of drought on wheat leaf cuticle properties

BACKGROUND: The plant cuticle is the outermost layer covering aerial tissues and is composed of cutin and waxes. The cuticle plays an important role in protection from environmental stresses and glaucousness, the bluish-white colouration of plant surfaces associated with cuticular waxes, has been suggested as a contributing factor in crop drought tolerance. However, the cuticle structure and composition is complex and it is not clear which aspects are important in determining a role in drought tolerance. Therefore, we analysed residual transpiration rates, cuticle structure and epicuticular wax composition under well-watered conditions and drought in five Australian bread wheat genotypes, Kukri, Excalibur, Drysdale, RAC875 and Gladius, with contrasting glaucousness and drought tolerance. RESULTS: Significant differences were detected in residual transpiration rates between non-glaucous and drought-sensitive Kukri and four glaucous and drought-tolerant lines. No simple correlation was found between residual transpiration rates and the level of glaucousness among glaucous lines. Modest differences in the thickness of cuticle existed between the examined genotypes, while drought significantly increased thickness in Drysdale and RAC875. Wax composition analyses showed various amounts of C31 ß-diketone among genotypes and increases in the content of alkanes under drought in all examined wheat lines. CONCLUSIONS: The results provide new insights into the relationship between drought stress and the properties and structure of the wheat leaf cuticle. In particular, the data highlight the importance of the cuticle’s biochemical makeup, rather than a simple correlation with glaucousness or stomatal density, for water loss under limited water conditions.Huihui Bi, Nataliya Kovalchuk, Peter Langridge, Penny J. Tricker, Sergiy Lopato, and Nikolai Borisju

Application of relativistic scattering theory of x rays to diffraction anomalous fine structure in Cu

We apply our recent first-principles formalism of magnetic scattering of circularly polarized x rays to a single Cu crystal. We demonstrate the ability of our formalism to interpret the crystalline environment related near-edge fine structure features in the resonant x-ray scattering spectra at the Cu K absorption edge. We find good agreement between the computed and measured diffraction anomalous fine structure features of the x-ray scattering spectra

Magnetic coupling in ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers

We report on a study of ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers using magnetometry and polarized neutron reflectivity (PNR). From depth-resolved characterization of the magnetic structure obtained by PNR, we concluded that the (Ga,Mn)As and (Al,Ga,Mn)As layers have in-plane and perpendicular-to-plane magnetic easy axes, respectively, with weak interlayer coupling. Therefore, the layer magnetizations align perpendicular to each other under low magnetic fields and parallel at high fields

Determination of protein thiol reduction potential by isotope labeling and intact mass measurement

Oxidation/reduction of thiol residues in proteins is an important type of post-translational modification that is implicated in regulating a range of biological processes. The nature of the modification makes it possible to define a quantifiable electrochemical potential, E⊕, for oxidation/reduction that allows cysteine-containing proteins to be ranked based on their propensity to be oxidized. Measuring oxidation of cysteine residues in proteins is difficult using standard electrochemical methods but recently top-down mass-spectrometry has been shown to enable the quantification of E⊕ for thiol oxidations. In this paper we demonstrate that mass spectrometry of intact proteins can be used in combination with an isotopic labeling strategy and an automated data analysis algorithm to measure E⊕ for the thiols in both E Coli Thioredoxin 1 and Human Thioredoxin 1. Our methodology relies on accurate mass measurement of proteins using LC-MS analyses and does not necessarily require top-down fragmentation. As well as analyzing homogeneous protein samples, we also demonstrate that our methodology can be used to determine thiol E⊕ measurements in samples which contain mixtures of proteins. Thus the combination of experiential methodology and data analysis regime have the potential to make such measurements in a high-throughput manner and in a manner more accessible to a broad community of protein scientists

Subdivision of the bacterioferritin comigratory protein family of bacterial peroxiredoxins based on catalytic activity.

© American Chemical Society,2010. Post-print version of article deposited in accordance with SHERPA RoMEO guidelinesPeroxiredoxins are ubiquitous proteins that catalyze the reduction of hydroperoxides, thus conferring resistance to oxidative stress. Using high-resolution mass spectrometry, we recently reclassified one such peroxiredoxin, bacterioferritin comigratory protein (BCP) of Escherichia coli, as an atypical 2-Cys peroxiredoxin that functions through the formation of an intramolecular disulfide bond between the active and resolving cysteine. An engineered E. coli BCP, which lacked the resolving cysteine, retained enzyme activity through a novel catalytic pathway. Unlike the active cysteine, the resolving cysteine of BCP peroxiredoxins is not conserved across all members of the family. To clarify the catalytic mechanism of native BCP enzymes that lack the resolving cysteine, we have investigated the BCP homologue of Burkholderia cenocepacia. We demonstrate that the B. cenocepacia BCP (BcBCP) homologue functions through a 1-Cys catalytic pathway. During catalysis, BcBCP can utilize thioredoxin as a reductant for the sulfenic acid intermediate. However, significantly higher peroxidase activity is observed utilizing glutathione as a resolving cysteine and glutaredoxin as a redox partner. Introduction of a resolving cysteine into BcBCP changes the activity from a 1-Cys pathway to an atypical 2-Cys pathway, analogous to the E. coli enzyme. In contrast to the native B. cenocepacia enzyme, thioredoxin is the preferred redox partner for this atypical 2-Cys variant. BCP-deficient B. cenocepacia exhibit a growth-phase-dependent hypersensitivity to oxidative killing. On the basis of sequence alignments, we believe that BcBCP described herein is representative of the major class of bacterial BCP peroxiredoxins. To our knowledge, this is the first detailed characterization of their catalytic activity. These studies support the subdivision of the BCP family of peroxiredoxins into two classes based on their catalytic activity

A comparison of collision cross section values obtained via travelling wave ion mobility-mass spectrometry and ultra high performance liquid chromatography-ion mobility-mass spectrometry : application to the characterisation of metabolites in rat urine

A comprehensive Collision Cross Section (CCS) library was obtained via Travelling Wave Ion Guide mobility measurements through direct infusion (DI). The library consists of CCS and Mass Spectral (MS) data in negative and positive ElectroSpray Ionisation (ESI) mode for 463 and 479 endogenous metabolites, respectively. For both ionisation modes combined, TWCCSN2 data were obtained for 542 non-redundant metabolites. These data were acquired on two different ion mobility enabled orthogonal acceleration QToF MS systems in two different laboratories, with the majority of the resulting TWCCSN2 values (from detected compounds) found to be within 1% of one another. Validation of these results against two independent, external TWCCSN2 data sources and predicted TWCCSN2 values indicated to be within 1-2% of these other values. The same metabolites were then analysed using a rapid reversed-phase ultra (high) performance liquid chromatographic (U(H)PLC) separation combined with IM and MS (IM-MS) thus providing retention time (tr), m/z and TWCCSN2 values (with the latter compared with the DI-IM-MS data). Analytes for which TWCCSN2 values were obtained by U(H)PLC-IM-MS showed good agreement with the results obtained from DI-IM-MS. The repeatability of the TWCCSN2 values obtained for these metabolites on the different ion mobility QToF systems, using either DI or LC, encouraged the further evaluation of the U(H)PLC-IM-MS approach via the analysis of samples of rat urine, from control and methotrexate-treated animals, in order to assess the potential of the approach for metabolite identification and profiling in metabolic phenotyping studies. Based on the database derived from the standards 63 metabolites were identified in rat urine, using positive ESI, based on the combination of tr, TWCCSN2 and MS data.</p