Investigation of biocatalytic properties of soybean seed hull peroxidase

Construction of the SHP-GLOX lignin regulation system and its application in rice straw

BACKGROUND

There is great productivity of rice(Oryza sativa L. spp. japonica) straw in China, which is a potential source of biomass for biofuel and forage. However, the high levels of lignins in rice straw limited its usage and induced the formation of agricultural waste. In order to modify the lignins contents to improve biofuel production and forage digestibility, we selected Soybean hull peroxidase (SHP) and Glyoxal oxidase (GLOX) as candidate genes to improve quality of rice straw. SHP, a class III plant peroxidase, is derived from multiple sources. It has several advantages, such as high resistance to heat, high stability under acidic and alkaline conditions, and a broad substrate range. SHP is speculated to be useful for lignin degradation. Glyoxal oxidase (GLOX) is an extracellular oxidase that can oxidize glyoxal and methylglyoxal in the extracellular medium to generate H2O2.

RESULTS

In the present study, the SHP and GLOX genes in pCAMBIA3301-glycine-rich protein (GRP)-SHP-GLOX, designated the K167 vector, were optimized and introduced into rice embryos using Agrobacterium-mediated transformation. Positive transgenic rice embryos were examined using molecular, physiological, biochemical and fermentation tests. The outcomes suggested that SHP degraded lignin effectively.

CONCLUSIONS

This research has created a rice breeding material with normal growth and yield but stalks that are more amenable to degradation in the later stage for use in breeding rice varieties whose stalks are easily used for energy. Our results will improve the industrial and commercial applications of rice straw.

Construction of arming Yarrowia lipolytica surface-displaying soybean seed coat peroxidase for use as whole-cell biocatalyst

Whole-cell biocatalysts could be used in wide-ranging applications. In this study, a new kind of whole-cell biocatalyst was successfully constructed by genetically immobilizing soybean seed coat peroxidase (SBP) on the cell surface of Yarrowia lipolytica Po1h, using a new integrative surface display expression vector (pMIZY05). The coding sequence of SBP was optimized and chemically synthesized, then inserted into pMIZY05 to generate expression plasmid pMIZY05-oEp. A DNA fragment corresponding to SBP and selection marker expression cassettes, without bacterial sequences, was released from pMIZY05-oEp by enzyme digestion and used to transform host yeast cells. A transformant (CM11) with a high recombinant SBP activity of 1571.9 U/mL was obtained, and recombinant SBP was proved to be successfully anchored on cell surface by testing the activities of different cellular fractions. After optimization of culture conditions, the recombinant SBP activity of CM11 was increased to 4187.8 U/mL. Afterwards, biochemical properties of the recombinant SBP were determined: optimum catalytic conditions were 37.5℃ at pH 3.5, and recombinant SBP exhibited high stability during thermal or acidic treatment. Recombinant activity of cell-displayed SBP was re-examined at optimum temperature and pH, which promoted an increase up to 4432.5 U/mL. To our knowledge, this represents the highest activity ever reported for heterologous expression of SBP. This study also provides a useful strategy for heterologous expression of proteins which could be toxic to intracellular content of host cells.

Soybean peroxidase immobilized onto silica-coated superparamagnetic iron oxide nanoparticles: Effect of silica layer on the enzymatic activity

Peroxidase immobilization onto magnetic supports is considered an innovative strategy for the development of technologies that involves enzymes in wastewater treatment. In this work, magnetic biocatalysts were prepared by immobilization of soybean peroxidase (SBP) onto different silica-coated superparamagnetic iron oxide nanoparticles. The obtained magnetic biocatalysts were tested for the degradation of malachite green (MG), a pollutant often found in industrial wastewaters and with significant drawbacks for the human and environmental health. A deep physicochemical characterization of the materials was performed by means of X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), High Resolution-Transmission Electron Microscope (HR-TEM) and magnetization measurements among others techniques. Results showed high immobilization yield of SBP onto nanomaterials with excellent properties for magnetic recoverability. A partial loss of activity with respect to free SBP was observed, compatible with the modification of the conformational structure of the enzyme after immobilization. The structural modification depended on the amount (and thickness) of silica present in the hybrid materials and the activity yield of 43% was obtained for the best biocatalyst. Thermal stability and reusability capacity were also evaluated.

Expression and characterization of soybean seed coat peroxidase in Escherichia coli BL21(DE3)

Soybean seed coat peroxidase (SBP) is a valuable enzyme having a broad variety of applications in analytical chemistry, biochemistry, and food processing. In the present study, the sscp gene (Gene ID: 548068) was optimized based on the preferred codon usage of Escherichia coli, synthesized, and expressed in E. coli BL21(DE3). SDS-PAGE and western blot analysis of this expressed protein revealed that its molecular weight is approximately 39 kDa. The effects of induction temperature, concentration of isopropyl-β-D-thiogalactoside and hemin, induction time, expression time were optimized to enhance SBP production with a maximum activity of 11.23 U/mL (8.64 U/mg total protein). Furthermore, the kinetics of enzyme-catalyzed reactions of recombinant protein was determined. When 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) was used as substrate, optimum reaction temperature and pH of the enzyme were 85°C and 5.0, respectively. The effects of metal ions on the enzymatic reaction were also further investigated. The SBP was successfully expressed in E. coli BL21(DE3) which would provide a more efficient production strategy for industrial applications of SBP.

Screening of three commercial plant peroxidases for the removal of phenolic compounds in membrane bioreactors

A comparative study of three plant peroxidases, horseradish (HRP), soybean (SBP) and artichoke (AKPC), was carried out to select the most appropriate one for 4-chlorophenol treatment in an ultrafiltration membrane reactor. Soybean peroxidase showed the highest enzymatic activity, followed by HRP and AKPC. The same tendency was observed in a discontinuous tank reactor, where SBP attained more than 90% of4-chlorophenol removal within the pH range tested. The optimum temperature was 30 degrees C, with SBP showing highest thermostability. With the ultrafiltration membrane reactor, SBP attained the highest operational stability, with 4-chlorophenol conversions of around 90% in the permeate stream for up to 200 minutes. Finally, permeate samples were analysed and no significant amount of enzyme was detected, so the observed loss of activity, less pronounced with SBP, was attributed to enzyme adsorption on the polymeric products deposited on the membrane surface. Soybean peroxidase was selected as the most appropriate peroxidase for future research.

Oxidative degradation of Remazol Turquoise Blue G 133 by soybean peroxidase

Reactive dyes are widely employed in textile industries and their removal from wastewaters is a relevant environmental problem. In addition to chemical and physical methods, several bioremediation approaches, involving intact micro-organisms or isolated enzymes, have been proposed to decolorize dye solutions. In this paper, we report the complete and fast decolourization of a Cu(II)-phthalocyanine based reactive dye (Remazol Turquoise Blue G 133) by means of the soybean peroxidase/H(2)O(2) system. The oxidative degradation of the dye in aqueous solution at 25°C was studied as function of pH, revealing a quantitative decolourization yield at acidic pH values with a maximum of activity at pH 3.3. The reaction products were identified and characterized by HPLC-diode array detector (DAD)-mass spectrometry (MS), ionic chromatography and EPR techniques. This analysis showed that the enzyme catalyses the breaking of the phthalocyanine ring producing sulfophthalimide as the main degradation product, and the release of stoichiometric amount of ammonium and Cu(II) ions.

Comparison of the different types of surfactants for the effect on activity and structure of soybean peroxidase

In the pH 2.6 and 5.2 systems, soybean peroxidase (SBP) (isoelectric point, pI 3.9) has positive and negative charge, respectively. In order to acquire detailed knowledge on the role played by electrostatics in the denaturation of proteins, a comparison of anionic surfactant sodium dodecyl sulfate (SDS), nonionic surfactant nonaethylene glycol monododecyl ether [C12H25O(CH2CH2O)9H] (AEO9), and cationic surfactant cetyltrimethylammonium bromide (CTAB) for the influences on the activity and structure of soybean peroxidase (SBP) was carried out by measuring the activity, far-UV circular dichrosm, fluorescence, and electronic absorption spectra of SBP in the pH 2.6 and 5.2 systems at 30 degrees C. In the pH 2.6 systems, the interaction of SDS with SBP results in an increase in the fluorescence intensity with a red shift of the emission maximum of the tryptophan fluorescence and a blue shift of the Soret band. In the meantime, the alpha-helix of SBP is unfolded and the activity of SBP is lost irreversibly. In pH 5.2 systems, the fluorescence spectra features of SBP are similar to those in pH 2.6 systems with increasing SDS concentration, but a red shift of Soret band as well as an alteration of the tertiary structure of SBP occurs, and the lost activity is recoverable. The electrostatic interactions between SBP and SDS play an important role in the denaturation of SBP. The effects of AEO9 and CTAB in pH 2.6 and 5.2 systems on the activity and spectral features of SBP are similar to that of SDS in pH 5.2 systems, but AEO9 is prone to unfold the beta-sheet of SBP in pH 2.6 systems. The electrostatic interactions of CTAB with SBP are not the primary elements for denaturation of SBP, which distinctly differ from those of SDS. These results can be useful with respect to wide applications of the surfactants in the separation and purification of proteins.

A comparative study of free and immobilized soybean and horseradish peroxidases for 4-chlorophenol removal: protective effects of immobilization

Horseradish peroxidase (HRP) and soybean peroxidase (SBP) were covalently immobilized onto aldehyde glass through their amine groups. The activity yield and the protein content for the immobilized SBP were higher than for the immobilized HRP. When free and immobilized peroxidases were tested for their ability to remove 4-chlorophenol from aqueous solutions, the removal percentages were higher with immobilized HRP than with free HRP, whereas immobilized SBP needs more enzyme to reach the same conversion than free enzyme. In the present paper the two immobilized derivatives are compared. It was found that at an immobilized enzyme concentration in the reactor of 15 mg l(-1), SBP removed 5% more of 4-chlorophenol than HRP, and that a shorter treatment was necessary. Since immobilized SBP was less susceptible to inactivation than HRP and provided higher 4-chlorophenol elimination, this derivative was chosen for further inactivation studies. The protective effect of the immobilization against the enzyme inactivation by hydrogen peroxide was demonstrated.