Methyl Parathion Hydrolase Research Articles

Surface display of MPH on Pseudomonas putida JS444 using ice nucleation protein and its application in detoxification of organophosphates

Methyl parathion hydrolase (MPH) has been displayed on the surface of microorganisms for the first time using only N- and C-terminal domains of the ice nucleation protein (INPNC) from Pseudomonas syringae INA5 as an anchoring motif. A shuttle vector pINCM coding for INPNC-MPH was constructed and used to target MPH onto the surface of a natural p-nitrophenol (PNP) degrader, Pseudomonas putida JS444, overcoming the potential substrate uptake limitation. Over 90% of the MPH activity was located on the cell surface as determined by protease accessibility and cell fractionation experiments. The surface localization of the INPNC-MPH fusion was further verified by Western blot analysis and immunofluorescence microscopy. The engineered P. putida JS444 degraded organophosphates as well as PNP rapidly without growth inhibition. Compared to organophosphorus hydrolase-displaying systems reported, changes in substrate specificity highlight an important potential use of the engineered strain for the clean-up of specific organophosphate nerve agents.

Simultaneous biodegradation of methyl parathion and carbofuran by a genetically engineered microorganism constructed by mini-Tn5 transposon

A genetically engineered microorganism (GEM) capable of simultaneous degrading methyl parathion (MP) and carbofuran was successfully constructed by random insertion of a methyl parathion hydrolase gene (mpd) into the chromosome of a carbofuran degrading Sphingomonas sp. CDS-1 with the mini-transposon system. The GEM constructed was relatively stable and cell viability and original degrading characteristic was not affected compared with the original recipient CDS-1. The effects of temperature, initial pH value, inoculum size and alternative carbon source on the biodegradation of MP and carbofuran were investigated. GEM cells could degrade MP and carbofuran efficiently in a relatively broad range of temperatures from 20 to 30 degrees C, initial pH values from 6.0 to 9.0, and with all initial inoculation cell densities (10(5)-10(7) CFU ml(-1)), even if alternative glucose existed. The optimal temperature and initial pH value for GEM cells to simultaneously degrade MP and carbofuran was at 30 degrees C and at pH 7.0. The removal of MP and carbofuran by GEM cells in sterile and non-sterile soil were also studied. In both soil samples, 50 mg kg(-1) MP and 25 mg kg(-1) carbofuran could be degraded to an undetectable level within 25 days even if there were indigenous microbial competition and carbon sources effect. In sterile soil, the biodegradation rates of MP and carbofuran were faster, and the decline of the inoculated GEM cells was slower compared with that in non-sterile soil. The GEM constructed in this study was potential useful for pesticides bioremediation in natural environment.

Parameters controlling the gene-targeting frequency at the Sphingomonas species rrn site and expression of the methyl parathion hydrolase gene

To investigate the key parameters controlling the exogenous methyl parathion hydrolase (MPH) gene mpd-targeting frequency at the ribosomal RNA operon (rrn) site of Sphingomonas species which has a wide range of biotechnological applications. Targeting vectors with different homology lengths and recipient target DNA with different homology identities were used to investigate the parameters controlling the targeting frequency at the Sphingomonas species rrn site. Targeting frequency decreased with the reduction of homology length, and the minimal size for normal homologous recombination was >100 bp. Homologous recombination could succeed even if there were 3-4% mismatches; however, targeting frequency decreased with increasing sequence divergence. The Red recombination system could increase the targeting frequency to some extent. Targeting of the mpd gene to the rrn site did not affect cell viability and resulted in an increase of MPH-specific activity in recombinants. Targeting frequency was affected by homology length, identity and the Red recombination system. The rrn site is a good target site for the expression of exogenous genes. This work is useful as a foundation for a better understanding of recombination events involving homologous sequences and for the improved manipulation of Sphingomonas genes in biotechnological applications.

Construction of a genetically engineered microorganism for degrading organophosphate and carbamate pesticides

Abstract Genetically engineered microorganisms (GEMs) have shown potential for enhanced degradation of a range of substrates. In this study, a DNA fragment including the open reading frame of mpd (methyl parathion hydrolase encoding gene) and cognate regulator of a methyl parathion (MP)-degrading strain Pseudomonas putida DLL-1 was cloned by the shotgun method. The fragment was cloned into a broad-host vector pBBR1MCS-2 to produce a recombinant plasmid pBBR-mpd. CDS-pBBR-mpd, a GEM, was successfully constructed by transforming it into a carbofuran-degrading strain Sphingomonas sp. CDS-1, and it degraded both carbofuran and MP. CDS-pBBR-mpd maintained stable and high MP hydrolase activity (50.72 nmol min−1 μg−1 protein, which was 6.57 times higher than that of P. putida strain DLL-1). and appears to be a promising GEM for environmental bioremediation.

Crystal Structure of Methyl Parathion Hydrolase from Pseudomonas sp. WBC-3

Methyl parathion hydrolase (MPH, E.C.3.1.8.1), isolated from the soil-dwelling bacterium Pseudomonas sp. WBC-3, is a Zn(II)-containing enzyme that catalyzes the degradation of the organophosphate pesticide methyl parathion. We have determined the structure of MPH from Pseudomonas sp. WBC-3 to 2.4 angstroms resolution. The enzyme is dimeric and each subunit contains a mixed hybrid binuclear zinc center, in which one of the zinc ions is replaced by cadmium. In both subunits, the more solvent-exposed beta-metal ion is substituted for Cd2+ due to high cadmium concentration in the crystallization condition. Both ions are surrounded by ligands in an octahedral arrangement. The ions are separated by 3.5 angstroms and are coordinated by the amino acid residues His147, His149, Asp151, His152, His234 and His302 and a water molecule. Asp255 and a water molecule serve to bridge the zinc ions together. MPH is homologous with other metallo-beta-lactamases but does not show any similarity to phosphotriesterase that can also catalyze the degradation of methyl parathion with lower rate, despite the lack of sequence homology. Trp179, Phe196 and Phe119 form an aromatic cluster at the entrance of the catalytic center. Replacement of these three amino acids by alanine resulted in a significant increase of K(m) and loss of catalytic activity, indicating that the aromatic cluster has an important role to facilitate affinity of enzyme to the methyl parathion substrates.

Plasmid-borne catabolism of methyl parathion and p-nitrophenol in Pseudomonas sp. strain WBC-3

Pseudomonas sp. strain WBC-3 utilises methyl parathion (MP) or p-nitrophenol (PNP) as the sole source of carbon, nitrogen, and energy. A plasmid designated pZWL0 of ≈70 kb in this strain was found to be responsible for MP and PNP degradation. This was based on the fact that the plasmid-cured strains showed PNP −MP − phenotype and the PNP +MP + phenotype could be conjugally transferred. We have also cloned a 3.4-kb HindIII fragment which exhibited methyl parathion hydrolase activity, which revealed a methyl parathion hydrolase ( mph) gene whose DNA sequence is 99.5% identical to the recently identified mpd gene from Plesiomonas sp. M6 [C. Zhongli, L. Shunpeng, F. Guoping, Isolation of methyl parathion-degrading strain M6 and cloning of the methyl parathion hydrolase gene, Appl. Environ. Microbiol. 67 (2001) 4922–4925]. The mph gene was functionally expressed in Escherichia coli and the relative activities of the enzyme against different substrates were determined. The sequence alignment and phylogenetic analysis suggested that MPH and MPD evolved independently from other well-studied organophosphate hydrolases and may be originated from class B β-lactamase family. Subsequently obtained a 6.5-kb KpnI and BamHI fragment containing the above HindIII fragment revealed that the mph gene was physically located in a typical transposon.

High-Level Expression and Secretion of Methyl Parathion Hydrolase in Bacillus subtilis WB800

The methyl parathion hydrolase (MPH)-encoding gene mpd was placed under the control of the P43 promoter and Bacillus subtilis nprB signal peptide-encoding sequence. High-level expression and secretion of mature, authentic, and stable MPH were achieved using the protease-deficient strain B. subtilis WB800 as the host.

Construction and application of a promoter-trapping vector with methyl parathion hydrolase gene mpd as the reporter.

A facilitative and efficient promoter-trapping vector, pUC-mpd, was constructed with the promoterless methyl parathion hydrolase gene as the reporter. This reporter gene is easily used to clone promoters with different promoting strength on selective plates. Promoter regions of the ytkA and ywoF genes with strong promoting and signal peptide functions were cloned from the Bacillus subtilis 168 genomic promoter library with this vector.

Expression, purification, and characterization of a novel methyl parathion hydrolase

The mpd gene coding for a novel methyl parathion hydrolase (MPH) was previously reported and its putative open reading frame was also identified. To further confirm its coding region, the intact region encoding MPH was obtained by PCR and expressed in Escherichia coli as a hexa-His C-terminal fusion protein. The fusion protein was purified to homogeneity by metal-affinity chromatography. The enzyme activity and zymogram assay showed that the fusion protein was functional in degrading methyl parathion. The amino terminal sequencing of the purified recombinant MPH indicated that a signal peptide of the first 35 amino acids was cleaved from its precursor to form active MPH. A rat polyclonal antiserum was raised against the purified mature fusion protein. The results of Western blot and zymogram demonstrated that mature MPH in native Plesiomonas sp. strain M6 was also processed from its precursor by cleavage of a putative signal peptide at the amino terminus. The production of active MPH in E. coli was greatly improved after the coding region for the signal peptide was deleted. HPLC gel filtration of the purified mature recombinant MPH revealed that the MPH was a monomer.

Crystallization and preliminary X-ray studies of methyl parathion hydrolase from Pseudomonas sp. WBC-3.

Methyl parathion hydrolase (MPH) from Pseudomonas sp. WBC-3, an enzyme that catalyzes the degradation of methyl parathion (O,O-dimethyl O-p-nitrophenyl phosphorothioate; MP), has been purified and crystallized by the hanging-drop vapour-diffusion method. The crystals were grown at 291 K using a precipitant solution consisting of 30% PEG 400, 0.1 M sodium acetate pH 4.6, 0.1 M CdCl(2). MPH is a zinc-containing enzyme judged by inductively coupled plasma mass-spectrometric (ICP-MS) analysis. Multiple-wavelength anomalous dispersive X-ray data were collected at 2.5 A resolution from a single crystal on beamline 41XU at SPring-8. The crystal belongs to space group P4(3)2(1)2, with unit-cell parameters a = 84.94, b = 84.94, c = 200.38 A, alpha = beta = gamma = 90 degrees. The asymmetric unit contains two molecules and has a solvent content of approximately 52%. Crystal structure determination is in progress.

Isolation of methyl parathion-degrading strain M6 and cloning of the methyl parathion hydrolase gene.

A degradative bacterium, M6, was isolated and presumptively identified as Plesiomonas sp. strain M6 was able to hydrolyze methyl parathion to p-nitrophenol. A novel organophosphate hydrolase gene designated mpd was selected from its genomic library prepared by shotgun cloning. The nucleotide sequence of the mpd gene was determined. The gene could be effectively expressed in Escherichia coli.