Recombinant rice xylanase inhibitor (RIXI) expressed in Escherichia coli and its inhibitory activity on family GH11endo-xylanases.

The rice xylanase inhibitor gene, rixi, was cloned from rice genome. The open reading frame of rixi was 915 bp and encoded 304 amino acids with the theoretical molecular mass of 33.9 kDa. The rixi was inserted into the new-type expression vector pCold TF, and was high-level expressed in Escherichia coli BL21 (DE3). SDS-PAGE and Western blot analysis revealed that the molecular weight of the recombinant rice xylanase inhibitor, namely reERIXI, was approximately 89.8 kDa. The reERIXI exhibited significant inhibitory activities against several family GH11 xylanases. After interaction with reERIXI, the residual activity of reBaxA50 and TfxA_CD214 were 59.24% and 44.41%, respectively. The optimal temperature of reERIXI inhibitory activity to reBaxA50 and TfxA_CD214 were 60 °C and 50 °C, respectively. The thermostability assay revealed that reERIXI was stable below 60 °C. reERIXI showed high inhibitory when interacting with reBaxA50 and TfxA_CD214 for 30-60 min. The intrinsic fluorescence spectroscopy of reBaxA50 and TfxA_CD214 was quenched with increasing reERIXI concentration. Circular dichroism measurement revealed that ratio of helix of reBaxA50 and ratio of beta of TfxA_CD214 significantly decreased when interacting with reERIXI. The total concentration of hydrolytic products from beechwood xylan decreased when reERIXI was added.

Recombinant Bacillus amyloliquefaciens xylanase A expressed in Pichia pastoris and generation of xylooligosaccharides from xylans and wheat bran.

In this study, BaxA (GenBank: KM624029), which encodes the Bacillus amyloliquefaciens xylanase A (BaxA), was highly expressed in Pichia pastoris GS115 under the control of the AOX1 promoter. The recombinant xylanase, namely rePBaxA, was purified to homogeneity by using Ni-affinity resin and its molecular weight was 35.0kDa. The optimum temperature and pH of rePBaxA were 50°C and 5.0, respectively. The kinetic parameters Michaelis-Menten constant (Km) and maximum reaction rate (Vmax) of rePBaxA were 5.41mg/mL and 22.42µmol/min/mL, respectively. High-performance liquid chromatography results showed that after 6h of hydrolysis, rePBaxA released xylose-xylohexaose (X1-X6) mixture from beechwood and birchwood xylan, with xylobiose (X2) and xylotriose (X3) as the major products, respectively. The hydrolyates from oat spelt, wheat bran insoluble xylan and pretreated wheat bran by rePBaxA included X2-X6, with X6 having the highest concentration. The mode of action analysis revealed that rePBaxA was an endo-acting xylanase with transglycosylation activity. X2 might be the minimum oligomer hydrolyzed by rePBaxA. The pretreated wheat bran and wheat bran insoluble xylan could be directly hydrolyzed by rePBaxA. This study provided a basis for using agricultural waste by-products as substrates for manufacting value-added probiotics, namely, xylooligosaccharides.

Recombination of thermo-alkalistable, high xylooligosaccharides producing endo-xylanase from Thermobifida fusca and expression in Pichia pastoris.

For xylooligosaccharide (XO) production, endo-xylanase from Thermobifida fusca was modified by error-prone PCR and DNA shuffling. The G4SM1 mutant (S62T, S144C, N198D, and A217V) showed the most improved hydrolytic activity and was two copies expressed in Pichia pastoris under the control of GAP promoter. The maximum xylanase activity in culture supernatants was 165 ± 5.5 U/ml, and the secreted protein concentration reached 493 mg/l in a 2-l baffled shake flask. After 6× His-tagged protein purification, the specific activity of G4SM1 was 2036 ± 45.8 U/mg, 2.12 times greater than that of wild-type enzyme. Additionally, G4SM1 was stable over a wide pH range from 5.0 to 9.0. Meanwhile, half-life of G4SM1 thermal inactivation at 70 °C increased 8.5-fold. Three-dimensional structures suggest that two amino acid substitutions, S62T and S144C, located at catalytic domain may be responsible for the enhanced activity and thermostability of xylanase. Xylobiose was the dominant end product of xylan hydrolysis by G4SM1. Due to its attractive biochemical properties, G4SM1 has potential value in commercial XO production.

Enhancing catalytic activity of a hybrid xylanase through single substitution of Leu to Pro near the active site.

A modified error-prone PCR and high-throughout screening system based on 96-well plate were employed to improve catalytic activity of a hybrid xylanase (ATx). The mutant (FSI-A124) with enhanced activity was further heterologously expressed in Pichia pastoris under the control of GAP promoter. The recombinant xylanase driven by the Saccharomyces cerevisiae α-mating factor was secreted into culture medium. After growth in YPD medium for 96 h, xylanase activity in the culture supernatant reached 66.1 U ml(-1), which was 2.92 times as that of its parent. 6 × His-tagged purification increased the specific activity to 1557.61 U mg(-1). The optimum temperature and pH of recombinant xylanase were 55°C and 6.0, respectively. A single amino acid substitution (L49P) was observed within sequence of the mutant. Insight of the three dimensional structure revealed that proline possibly produced weaker hydrogen bond, van der Waals force and hydrophobic interaction with other residues nearby than leucine, especially for V174, contributing to the flexibility of catalytic residue E177. In this study, FSI-A124 exhibited higher xylanase activity but poorer thermostability than its parent, indicating that activity and stability might be negatively correlated.

[Recent research progress of biogenesis and functions of miRNA*].

MicroRNA*s are about 22nt noncoding RNAs, which are processed from precursors with a characteristic hairpin secondary structure in the biogenesis of microRNAs. Recently, miRNA* strands were shown to mediate post-transcriptional regulatory networks, rather than serve merely as non-functional by-product in general view. Unlike miRNAs bound to AGO1, miRNA* strands are bound to AGO2 to form RISC duplex to mediate RNAi, which is similar to siRNA. This paper mainly reviewed the recent research progresses on miRNA*, such as the biosynthesis, biological characteristics, and functions.

Identification and proteomic analysis of a novel gossypol-degrading fungal strain.

BACKGROUND: Cottonseed meal, an important source of feed raw materials, has limited use in the feed industry because of the presence of the highly toxic gossypol. The aim of the current work was to isolate the gossypol-degrading fungus from a soil microcosm and investigate the proteins involved in gossypol degradation. RESULTS: A fungal strain, AN-1, that uses gossypol as its sole carbon source was isolated and identified as Aspergillus niger. A large number of intracellular proteins were detected using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but no significant difference was observed between the glucose-containing and gossypol-containing mycelium extracts. Two-dimensional gel electrophoresis results showed that the protein spots were concentrated in the 25.0-66.2 kDa range and distributed in different pI gradients. PDQuest software showed that 51 protein spots in the gels were differentially expressed. Of these, 20 differential protein spots, including six special spots expressed in gossypol, were analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. CONCLUSION: The fungus AN-1 biodegraded gossypol and the proteomic analysis results indicate that some proteins were involved in the gossypol biodegradation during fungus survival, using gossypol as its sole carbon source.

Effects of zinc supplementation and deficiency on bone metabolism and related gene expression in rat.

One hundred male rats were randomly divided into four groups (n = 25) and fed a Zn-adequate diet (ZA, 46.39 mg/kg), Zn-deficient diet (ZD, 3.20 mg/kg), Zn-overdose diet (ZO, 234.39 mg/kg), or were pair-fed a Zn-adequate diet (PF) for 5 weeks, respectively. The body weight, femur weight, and activity of alkaline phosphatase (ALP) were reduced in the ZD group but were increased in the ZO group. Zn concentrations in both liver and femur were elevated in the ZO group, whereas femur Zn was decreased in the ZD group. The concentrations of calcium and phosphorus were lower in the ZD than those in other groups. Serum calcium concentration was decreased in the ZD. The relative expression level of ALP was decreased in both ZD and PF, and no significant differences were observed between ZO and ZA. Insulin-like growth factor-I (IGF-I) mRNA level was reduced in the ZD but unchanged in the ZO and PF group. Zn deficiency also decreased ALP mRNA level as compared with that of PF group. Carbonic anhydrase II mRNA level was not affected by Zn. Nevertheless, dietary Zn influenced the growth, bone metabolism, and expression of IGF-I and ALP in male growing rats.

Hydrolytic properties of a hybrid xylanase and its parents.

The hydrolytic properties of a hybrid xylanase (ATx) and its parents (reAnxA and reTfxA) were studied using xylans and xylooligosaccharides as substrates. Analysis of reaction mixtures by high-performance liquid chromatograph revealed that xylotriose (X3) was the main product released from birchwood xylan and wheat bran insoluble xylan by ATx and reAnxA, respectively. Xylobiose (X2) was the main product separately released from birchwood xylan and wheat bran insoluble xylan by reTfxA. Xylotetraose (X4), xylopentaose (X5), and xylohexaose (X6) could be hydrolyzed by ATx, which showed no activity on X2 and X3. Therefore, X4 might be the minimum oligomer hydrolyzed by ATx. X2-X6 could be hydrolyzed by reAnxA and reTfxA, respectively. All of ATx, reAnxA, and reTfxA showed transglycosylation activity.

Effects of zinc on hepatic antioxidant systems and the mRNA expression levels assayed by cDNA microarrays in rats.

BACKGROUND: This study evaluated effects of zinc on the hepatic lipid peroxidation, antioxidant components and mRNA expression levels in rats. METHODS: Three diets with different Zn levels including Zn adequacy (ZA; 34.50 mg/kg, control), Zn deficiency (ZD; 3.30 mg/kg), and Zn overdose (ZO; 345.45 mg/kg) were fed to rats for 6 weeks. The mRNA expression levels were analyzed by cDNA microarrays. RESULTS: The body weight of rats fed the ZD diet was less (p < 0.01) than that of rats fed the ZA diet. Zn overdose elevated body weight, but the increase was not detected (p > 0.05) at week 6. Although copper and iron status in serum were declined (p < 0.01), those in liver were not affected (p > 0.05) by the high intake of zinc. The glutathione peroxidase (GPx) and glutathione (GSH) remained unchanged (p > 0.05) by zinc treatment. Rats fed the ZD diet showed reductions(p < 0.01) in the Cu-Zn superoxide dismutase (Cu-Zn SOD) and catalase (CAT) activity, and increases (p < 0.01) in the malondialdehyde and hydrogen peroxide (H(2)O(2)) contents. Rats fed the ZO diet particularly had higher Cu-Zn SOD (p < 0.01) activity. The mRNA expression levels of SOD were upregulated in the ZO group, and CAT was downregulated in the ZD group, while no changes in GPx mRNA levels were found after zinc treatment. CONCLUSION: The study suggested that zinc deficiency largely decreased body weight; zinc overdose, however, moderately stimulated growth in the early growing phase of rats. High dietary zinc did not compete with liver copper and iron status. Although Zn deficiency impaired antioxidant functions, zinc overdose hardly enhanced the antioxidant systems of animals.

Insights on zinc regulation of food intake and macronutrient selection.

Zinc (Zn) is an essential trace element required for human beings and animals. This divalent cation is involved in many physiological functions, including immune and antioxidant function, growth, and reproduction. Deficiency of Zn produces several pathological disorders and abnormalities in its metabolism, such as anorexia, weight loss, poor efficiency, and growth retardation. Although it has been known for more than 50 yr that Zn deficiency regularly and consistently causes anorexia in many animal species, the mechanism that causes this phenomenon still remains an enigma. The present review describes recent research investigating the relationship between Zn deficiency and the regulation of food intake, as well as macronutrient selection.

Distribution and characteristics of endogenous digestive enzymes in the red-eared slider turtle, Trachemys scripta elegans.

Distribution and properties of the main digestive enzymes including protease and amylase, from stomach, pancreas and the anterior, middle and posterior intestine of the adult red-eared slider turtle Trachemys scripta elegans were studied at various pHs and temperatures. The optimum temperature and pH for protease in stomach, pancreas and the anterior, middle and posterior intestine were 40 degrees C, 2.5; 50 degrees C, 8.0; 50 degrees C, 7.0; 50 degrees C, 8.0; and 50 degrees C, 8.5; respectively. The optimum temperature and pH for amylase in stomach, pancreas and anterior, middle and posterior intestine were 40 degrees C, 8.0; 30 degrees C, 7.5; 40 degrees C, 7.0; 50 degrees C, 8.0; and 50 degrees C, 8.0; respectively. Under the optimum conditions, the order of protease activity from high to low was of pancreas, stomach and the anterior, posterior and middle intestine; the activity of amylase in descending order was of anterior intestine, pancreas, posterior intestine, middle intestine and stomach.

Characteristics of photosynthesis and functions of the water-water cycle in rice (Oryza sativa) leaves in response to potassium deficiency.

The mechanisms of photoprotection of photosynthesis and dissipation of excitation energy in rice leaves in response to potassium (K) deficiency were investigated. Net photosynthetic rate and the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase decreased under K deficiency. Compared with the control, non-photochemical quenching of Chl fluorescence increased in K-deficient plant, whereas the efficiency of excitation transfer (F'(v)/F'(m)) and the photochemical quenching coefficient (q(P)) decreased. Thus, thermal dissipation of excitation energy increased as more excess electrons were accumulated in the photosynthetic chain. The electron transport rate through PSII (J(f)) was more sensitive to O2 concentration, and the fraction of electron transport rate required to sustain CO2 assimilation and photorespiration (J(g)/J(f)) was significantly decreased under K deficiency compared with the control. Furthermore, the alternative electron transport (J(a)/J(f)) was increased, indicating that a considerable amount of electrons had been transported to O2 during the water-water cycle in the K-deficient leaves. Although the fraction of electron transport to photorespiration (J(o)/J(f)) was also increased in the K-deficient leaves, it was less sensitive than that of the water-water cycle. With the generation of reactive oxygen species level, the activities of superoxide dismutase and ascorbate peroxidase, two of the key enzymes involved in scavenging of active oxygen species in the water-water cycle, also increased in K-deficient rice. Therefore, it is likely that a series of photoprotective mechanisms were initiated in rice plants in response to K deficiency and the water-water cycle might be critical for protecting photosynthetic apparatus under K deficiency in rice.

Expression of recombinant Aspergillus niger xylanase A in Pichia pastoris and its action on xylan.

The mature peptide of Aspergillus niger xylanase A (AnxA) was successfully expressed in Pichia pastoris at high levels under the control of AOX1 promoter. The recombinant AnxA (reAnxA) was secreted into culture medium. After 96-h 0.25% methanol induction, the activity of reAnxA in the culture supernatant reached the peak, 175 U/mg, which was 1.9 times as high as that of the native AnxA (92 U/mg). Studies on enzymatic properties showed that the optimum temperature and optimum pH of reAnxA were 50 degrees C and 5.0, respectively. The reAnxA was very stable in a wide pH range of 3.0-8.0. After incubation at the pH 3.0-8.0, 25 degrees C for 1h, all the residual activities of reAnxA were over 80%. The K(m) and k(cat) values for reAnxA were 4.8 mg/ml and 123.2s(-1), respectively. HPLC analysis showed that xylotriose was the main hydrolysis product of birchwood xylan and bran insoluble xylan by reAnxA.

Construction, expression, and characterization of a thermostable xylanase.

A hybrid gene, btx, encoding a thermostable xylanase, Btx, was constructed by substituting the 31 N-terminal amino acid residues of the Thermomonospora fusca xylanase A (TfxA) for the corresponding region of 22 amino acid residues of the Bacillus subtilis xylanase A (BsxA). The btx gene was expressed in Escherichia coli BL21. The halo size produced by xylanase Btx on a Remanzol brilliant blue R (RBB) xylan plate at 60 degrees C and pH 6.0 was larger than those of BsxA and TfxA. The molecular weight of Btx was 22 kDa. Temperature and pH optima for Btx were at 50-60 degrees C and 6.0, respectively. Btx showed activity over 80% over a pH range of 5.0-9.0, which was wider than that of BsxA, and was also more acid-resistant than TfxA. Btx exhibited significant thermostability compared with BsxA. The results show the importance of the N-terminal sequence of TfxA in thermostability.