Junqi Zhao

High-pressure synthesis of orthorhombic SrIrO3 perovskite and its positive magnetoresistance

The orthorhombic SrIrO3 perovskite was synthesized under 5GPa and 1000°C. It is paramagnetic below about 170K and transfers to an unknown magnetism under higher temperature. A band type metal to insulator transition caused by a pseudogap was observed at about 44K. Interestingly a positive magnetoresistance, i.e., resistance increased with applying magnetic field, was observed in the orthorhombic SrIrO3 perovskite below about 170K.

An Acidophilic and Acid-Stable β-Mannanase from Phialophora sp. P13 with High Mannan Hydrolysis Activity under Simulated Gastric Conditions

A beta-mannanase gene, man5AP13, was cloned from Phialophora sp. P13 and expressed in Pichia pastoris. The deduced amino acid sequence of the mature enzyme, MAN5AP13, had highest identity (53%) with the glycoside hydrolase family 5 beta-mannanase from Bispora sp. MEY-1. The purified recombinant beta-mannanase was acidophilic and acid stable, exhibiting maximal activity at pH 1.5 and retaining >60% of the initial activity over the pH range 1.5-7.0. The optimum temperature was 60 degrees C. The specific activity, K(m) and V(max) for locust bean gum substrate were 851 U/mg, 2.5 mg/mL, and 1667.7 U/min.mg, respectively. The enzyme had excellent activity and stability under simulated gastric conditions, and the released reducing sugar of locust bean gum was significantly enhanced by one-fold in simulated gastric fluid containing pepsin in contrast to that without pepsin. All these properties make MAN5AP13 a potential additive for use in the food and feed industries.

Two neutral thermostable cellulases from Phialophora sp. G5 act synergistically in the hydrolysis of filter paper.

Two novel cellulase genes, cbh6A and egGH45, were cloned from Phialophora sp. G5 and successfully expressed in Pichia pastoris. The putative polypeptide of CBH6A consists of a family 1 CBM and a catalytic domain of glycosyl hydrolase family 6 cellobiohydrolases, while deduced EgGH45 only contains a catalytic domain of family 45 endoglucanases. CBH6A and EgGH45 were optimally active at pH 7.0 and 65°C, and pH 6.0 and 60°C, respectively. Both enzymes exhibited high activities and stabilities over a wide pH range and had good thermostability at 70°C. CBH6A and EgGH45 had significant resistance to SDS (10mM), remaining 35% and 54% activities, respectively. These enzymes had synergic effect on the hydrolysis of filter paper, showing the highest efficiency in the ratio of CBH6A to EgGH45 at 80:20. The properties make this enzyme combination potential for application in textile and detergents industries.

A C-Terminal Proline-Rich Sequence Simultaneously Broadens the Optimal Temperature and pH Ranges and Improves the Catalytic Efficiency of Glycosyl Hydrolase Family 10 Ruminal Xylanases

ABSTRACT Efficient degradation of plant polysaccharides in rumen requires xylanolytic enzymes with a high catalytic capacity. In this study, a full-length xylanase gene (xynA) was retrieved from the sheep rumen. The deduced XynA sequence contains a putative signal peptide, a catalytic motif of glycoside hydrolase family 10 (GH10), and an extra C-terminal proline-rich sequence without a homolog. To determine its function, both mature XynA and its C terminus-truncated mutant, XynA-Tr, were expressed in Escherichia coli. The C-terminal oligopeptide had significant effects on the function and structure of XynA. Compared with XynA-Tr, XynA exhibited improved specific activity (12-fold) and catalytic efficiency (14-fold), a higher temperature optimum (50°C versus 45°C), and broader ranges of temperature and pH optima (pH 5.0 to 7.5 and 40 to 60°C versus pH 5.5 to 6.5 and 40 to 50°C). Moreover, XynA released more xylose than XynA-Tr when using beech wood xylan and wheat arabinoxylan as the substrate. The underlying mechanisms responsible for these changes were analyzed by substrate binding assay, circular dichroism (CD) spectroscopy, isothermal titration calorimetry (ITC), and xylooligosaccharide hydrolysis. XynA had no ability to bind to any of the tested soluble and insoluble polysaccharides. However, it contained more α helices and had a greater affinity and catalytic efficiency toward xylooligosaccharides, which benefited complete substrate degradation. Similar results were obtained when the C-terminal sequence was fused to another GH10 xylanase from sheep rumen. This study reveals an engineering strategy to improve the catalytic performance of enzymes.

Comparative Quantitative Analysis of Gene Expression Profiles of Glycoside Hydrolase Family 10 Xylanases in the Sheep Rumen during a Feeding Cycle

ABSTRACT Xylanase is a crucial hydrolytic enzyme that degrades plant polysaccharides in the rumen. To date, there is no information on the genetic composition and expression characteristics of ruminal xylanase during feeding cycles of ruminants. Here, the major xylanase of the glycoside hydrolase family 10 (GH 10) from the rumen of small-tail Han sheep was investigated during a feeding cycle. We identified 44 distinct GH 10 xylanase gene fragments at both the genomic and transcriptional levels. Comparison of their relative abundance showed that results from the evaluation of functional genes at the transcriptional level are more reliable indicators for understanding fluctuations in xylanase levels. The expression patterns of six xylanase genes, detected at all time points of the feeding cycle, were investigated; we observed a complex trend of gene expression over 24 h, revealing the dynamic expression of xylanases in the rumen. Further correlation analysis indicated that the rumen is a dynamic ecosystem where the transcript profiles of xylanase genes are closely related to ruminal conditions, especially rumen pH and bacterial population. Given the huge diversity and changing composition of enzymes over the entire rumen, this research provides valuable information for understanding the role of functional genes in the digestion of plant material.

Purification, gene cloning and characterization of an acidic β-1,4-glucanase from Phialophora sp. G5 with potential applications in the brewing and feed industries

An extracellular β-1,4-glucanase (CelG5, ∼55.0 kDa) was isolated from the culture filtrate of Phialophora sp. G5, and its encoding gene was cloned. The deduced amino acid sequence of CelG5 was at most 73.6% and 44.0%, respectively, identical with a hypothetical protein from Sordaria macrospora and an experimentally verified GH 7 endo-β-1,4-glucanase of Neurospora tetrasperma FGSC 2508. Native CelG5 had pH and temperature optima of pH 4.5-5.0 and 55-60°C. The enzyme showed some properties superior than most fungal β-1,4-glucanases, such as high activity over a wide pH range (exhibiting >50% of the maximum activity at pH 2.0-7.0), excellent stability in extreme acidic to alkaline conditions (pH 2.0-9.0), and strong resistance against pepsin and trypsin (retaining 89% and 94% activity, respectively). Recombinant CelG5 produced in Pichia pastoris had a molecular mass and a pH optimum similar to native CelG5, but with maximal activity at 65°C. Application tests showed that native CelG5 was stable under simulated gastric conditions (retaining >70% activity), and had capacity to decrease the viscosity of barley-bean feed (8.9% by 200 U CelG5) and mash (6.1% by 50 U CelG5) and increase the filtration rate of mash (18.4% by 50 U CelG5). These properties make CelG5 a good candidate for utilization in the animal feed and brewing industries.

Tunneling magnetoresistance and magnetic properties of Fe–Al2O3 nanogranular films

Tunneling giant magnetoresistance (MR) of the Fe–Al2O3 nanogranular films has been observed over a wide range of Fe volume fraction x and it took a maximum of 4.4% at room temperature for the film with x=0.45 at H=10 kOe. Furthermore, the field dependence of MR of the samples is well described by the form proportional to the square of the magnetization. Moreover, an estimate of the magnetic anisotropy energy density Ku increases with the decrease of x, yielding a value 2 orders of magnitude greater than the value for bulk Fe when x=0.23. The Bloch’s law, MS(T)=MS0(1−BTb), can also hold for all the samples but with nonbulk parameters dependent on the Fe volume fraction. These results reveal a percolation effect on the magnetic properties, as well as the conductance, in such nanogranular films.

The tandemly repeated domains of a β-propeller phytase act synergistically to increase catalytic efficiency

β‐Propeller phytases (BPPs) with tandemly repeated domains are abundant in nature. Previous studies have shown that the intact domain is responsible for phytate hydrolysis, but the function of the other domain is relatively unknown. In this study, a new dual‐domain BPP (PhyH) from Bacillus sp. HJB17 was identified to contain an incomplete N‐terminal BPP domain (PhyH‐DI, residues 41–318) and a typical BPP domain (PhyH‐DII, residues 319–644) at the C‐terminus. Purified recombinant PhyH and PhyH‐DII required Ca2+ for phytase activity, showed activity at low temperatures (0–35 °C) and pH 6.0–8.0, and remained active (at 37 °C) after incubation at 60 °C and pH 6.0–12.0. Compared with PhyH‐DII, PhyH is catalytically more active against phytate (catalytic constant 27.72 versus 4.17 s−1), which indicates the importance of PhyH‐DI in phytate degradation. PhyH‐DI was found to hydrolyze phytate intermediate d‐Ins(1,4,5,6) P4, and to act synergistically (a 1.2–2.5‐fold increase in phosphate release) with PhyH‐DII, other BPPs (PhyP and 168PhyA) and a histidine acid phosphatase. Furthermore, fusion of PhyH‐DI with PhyP or 168PhyA significantly enhanced their catalytic efficiencies. This is the first report to elucidate the substrate specificity of the incomplete domain and the functional relationship of tandemly repeated domains in BPPs. We conjecture that dual‐domain BPPs have succeeded evolutionarily because they can increase the amount of available phosphate by interacting together. Additionally, fusing PhyH‐DI to a single‐domain phytase appears to be an efficient way to improve the activity of the latter.

The effect of the interlayer on the exchange bias in FeMn/Cu/Co system

The effect of the Cu interlayer on the exchange bias in FeMn/Cu/Co trilayers has been investigated. It is found that a thin interlayer can lower the strength of the exchange coupling between antiferromagnetic and ferromagnetic layers. The temperature dependencies of the left and right coercivities show an entirely different behavior, and they are very similar, when the Cu is thin, to those of a FeMn/Co bilayer with a very thin antiferromagnetic layer. With increasing the thickness of the Cu interlayer, the bias field decreases in most cases, but at low temperature it still remains large even when the Cu thickness is as thick as 1.8 nm. When the temperature is lower than 150 K, the dependence of the exchange bias on the Cu interlayer thickness exhibits a fluctuation behavior. This behavior disappears gradually with increasing temperature.

Genetic diversity and expression profiles of cysteine phytases in the sheep rumen during a feeding cycle

Cysteine phytase is the main phytate‐degrading enzyme of ruminant animals. To explore the genetic diversity and dynamic expression profile of cysteine phytase in sheep rumen during a feeding cycle, four transcript (0, 4, 9 and 16 h after feeding) and one DNA (9 h after feeding) clone libraries were constructed, respectively. A total of 46 distinct gene fragments were identified, and most of these sequences had low identities (<60%) with known phytases. Great divergence was found in the constitution and abundance of genes at the genome and transcriptional levels, and the transcript data are more reliable to reflect the information of functional genes. Phylogenetic analysis indicated that the genes from uncultured bacteria instead of Firmicutes played the major phytate‐degrading role. Further comparative analysis revealed the dynamic constitution of cysteine phytase genes in rumen at different time points.