Bacterial detoxification of diisopropyl fluorophosphate

Enzymatic Degradation of Organophosphorus Pesticides and Nerve Agents by EC: 3.1.8.2

The organophosphorus substances, including pesticides and nerve agents (NAs), represent highly toxic compounds. Standard decontamination procedures place a heavy burden on the environment. Given their continued utilization or existence, considerable efforts are being made to develop environmentally friendly methods of decontamination and medical countermeasures against their intoxication. Enzymes can offer both environmental and medical applications. One of the most promising enzymes cleaving organophosphorus compounds is the enzyme with enzyme commission number (EC): 3.1.8.2, called diisopropyl fluorophosphatase (DFPase) or organophosphorus acid anhydrolase from Loligo Vulgaris or Alteromonas sp. JD6.5, respectively. Structure, mechanisms of action and substrate profiles are described for both enzymes. Wild-type (WT) enzymes have a catalytic activity against organophosphorus compounds, including G-type nerve agents. Their stereochemical preference aims their activity towards less toxic enantiomers of the chiral phosphorus center found in most chemical warfare agents. Site-direct mutagenesis has systematically improved the active site of the enzyme. These efforts have resulted in the improvement of catalytic activity and have led to the identification of variants that are more effective at detoxifying both G-type and V-type nerve agents. Some of these variants have become part of commercially available decontamination mixtures.

Prolidase - A protein with many faces

Prolidase is a metal-dependent peptidase specialized in the cleavage of dipeptides containing proline or hydroxyproline on their C-termini. Prolidase homologues are found in all kingdoms of life. The importance of prolidase in human health is underlined by a rare hereditary syndrome referred to as Prolidase Deficiency. A growing number of studies highlight the importance of prolidase in various other human conditions, including cancer. Some recent studies link prolidase's activity-independent regulatory role to tumorigenesis. Furthermore, the enzyme or engineered variants have some applications in biotechnology. In this short review, we aim to highlight different aspects of the protein the importance of which is increasingly recognized over the last years.

Biotechnological applications of recombinant microbial prolidases

Prolidase is a metallopeptidase that is ubiquitous in nature and has been isolated from mammals, bacteria and archaea. Prolidase specifically hydrolyzes dipeptides with a prolyl residue in the carboxy terminus (NH(2)-X-/-Pro-COOH). Currently, the only solved structure of prolidase is from the hyperthermophilic archaeon Pyrococcus furiosus. This enzyme is of particular interest because it can be used in many biotechnological applications. Prolidase is able to degrade toxic organophosphorus (OP) compounds, namely, by cleaving the P-F and P-O bonds in the nerve agents, sarin and soman. Applications using prolidase to detoxify OP nerve agents include its incorporation into fire-fighting foams and as biosensors for OP compound detection. Prolidases are also employed in the cheese-ripening process to improve cheese taste and texture. In humans, prolidase deficiency (PD) is a rare autosomal recessive disorder that affects the connective tissue. Symptoms of PD include skin lesions, mental retardation and recurrent respiratory infections. Enzyme replacement therapies are currently being studied in an effort to optimize enzyme delivery and stability for this application. Previously, prolidase has been linked to collagen metabolism and more recently is being associated with melanoma. Increased prolidase activity in melanoma cell lines has lead investigators to create cancer prodrugs targeting this enzyme. Thus, there are many biotechnological applications using recombinant and native forms of prolidase and this review will describe the biochemical and structural properties of prolidases as well as discuss their most current applications.

Fighting nerve agent chemical weapons with enzyme technology

The extreme toxicity of organophosphorous-based compounds has been known since the late 1930s. Starting in the mid-1940s, many nations throughout the world have been producing large quantities of organophosphorous (OP) nerve agents. Huge stockpiles of nerve agents have since developed. There are reportedly more than 200,000 tons of nerve agents in existence worldwide. There is an obvious need for protective clothing capable of guarding an individual from exposure to OP chemical weapons. Also, chemical processes that can effectively demilitarize and detoxify stored nerve agents are in great demand. The new and widely publicized Chemical Weapons Treaty requires such processes to soon be in place throughout the world. Biotechnology may provide the tools necessary to make such processes not only possible, but quite efficient in reducing the nerve agent dilemma. The following paper discusses some of the history in developing enzyme technology against nerve agents. Our laboratory has interest in enhancing the productivity and potential utility of these systems in both demilitarization and decontamination applications. Freeze-dried nerve agent-hydrolyzing enzyme preparations have been shown to be effective in decontaminating gaseous nerve agents. The direct incorporation of nerve agent-hydrolyzing enzymes within cross-linked polyurethane foam matrices during polymer synthesis has been shown to dramatically enhance the productivity of two different enzyme systems. The future goal of such work lies in building a bridge between the clinical application of nerve agent-hydrolyzing enzymes and practical processing techniques that may take advantage of the initial results already achieved in the laboratory.

Characterization of native and recombinant forms of an unusual cobalt-dependent proline dipeptidase (prolidase) from the hyperthermophilic archaeon Pyrococcus furiosus

Proline dipeptidase (prolidase) was purified from cell extracts of the proteolytic, hyperthermophilic archaeon Pyrococcus furiosus by multistep chromatography. The enzyme is a homodimer (39.4 kDa per subunit) and as purified contains one cobalt atom per subunit. Its catalytic activity also required the addition of Co2+ ions (Kd, 0.24 mM), indicating that the enzyme has a second metal ion binding site. Co2+ could be replaced by Mn2+ (resulting in a 25% decrease in activity) but not by Mg2+, Ca2+, Fe2+, Zn2+, Cu2+, or Ni2+. The prolidase exhibited a narrow substrate specificity and hydrolyzed only dipeptides with proline at the C terminus and a nonpolar amino acid (Met, Leu, Val, Phe, or Ala) at the N terminus. Optimal prolidase activity with Met-Pro as the substrate occurred at a pH of 7.0 and a temperature of 100 degrees C. The N-terminal amino acid sequence of the purified prolidase was used to identify in the P. furiosus genome database a putative prolidase-encoding gene with a product corresponding to 349 amino acids. This gene was expressed in Escherichia coli and the recombinant protein was purified. Its properties, including molecular mass, metal ion dependence, pH and temperature optima, substrate specificity, and thermostability, were indistinguishable from those of the native prolidase from P. furiosus. Furthermore, the Km values for the substrate Met-Pro were comparable for the native and recombinant forms, although the recombinant enzyme exhibited a twofold greater Vmax value than the native protein. The amino acid sequence of P. furiosus prolidase has significant similarity with those of prolidases from mesophilic organisms, but the enzyme differs from them in its substrate specificity, thermostability, metal dependency, and response to inhibitors. The P. furiosus enzyme appears to be the second Co-containing member (after methionine aminopeptidase) of the binuclear N-terminal exopeptidase family.

Biodegradation of organophosphorus pesticides by surface-expressed organophosphorus hydrolase

Organophosphorus hydrolase (OPH) was displayed and anchored onto the surface of Escherichia coli using an Lpp-OmpA fusion system. Production of the fusion proteins in membrane fractions was verified by immunoblotting with OmpA antisera. Inclusion of the organophosphorus hydrolase signal sequence was necessary for achieving enzymatic activity on the surface. More than 80% of the OPH activity was located on the cell surface as determined by protease accessibility experiments. Whole cells expressing OPH on the cell surface degraded parathion and paraoxon very effectively without any diffusional limitation, resulting in sevenfold higher rates of parathion degradation compared with whole cells with similar levels of intracellular OPH. Immobilization of these live biocatalysts onto solid supports could provide an attractive means for pesticide detoxification in place of immobilized enzymes, affording a reduced diffusional barrier.

Cloning and expression of a gene encoding a bacterial enzyme for decontamination of organophosphorus nerve agents and nucleotide sequence of the enzyme

Organophosphorus acid (OPA) anhydrolase enzymes have been found in a wide variety of prokaryotic and eukaryotic organisms. Interest in these enzymes has been prompted by their ability to catalyze the hydrolysis of toxic organophosphorus cholinesterase-inhibiting compounds, including pesticides and chemical nerve agents. The natural substrates for these enzymes are unknown. The gene (opaA) which encodes an OPA anhydrolase (OPAA-2) was isolated from an Alteromonas sp. strain JD6.5 EcoRI-lambda ZAPII chromosomal library expressed in Escherichia coli and identified by immunodetection with anti-OPAA-2 serum. OPA anhydrolase activity expressed by the immunopositive recombinant clones was demonstrated by using diisopropylfluorophosphate (DFP) as a substrate. A comparison of the recombinant enzyme with native, purified OPAA-2 showed they had the same apparent molecular mass (60 kDa), antigenic properties, and enzyme activity against DFP and the chemical nerve agents sarin, soman, and O-cyclohexyl methylphosphonofluoridate. The gene expressing this activity was found in a 1.74-kb PstI-HindIII fragment of the original 6.1-kb EcoRI DNA insert. The nucleotide sequence of this PstI-HindIII fragment revealed an open reading frame of 1,551 nucleotides, coding for a protein of 517 amino acid residues. Amino acid sequence comparison of OPAA-2 with the protein database showed that OPAA-2 is similar to a 647-amino-acid sequence produced by an open reading frame which appears to be the E. coli pepQ gene. Further comparison of OPAA-2, the E. coli PepQ protein sequence, E. coli aminopeptidase P, and human prolidase showed regions of different degrees of similarity or functionally conserved amino acid substitutions. These findings, along with preliminary data confirming the presence of prolidase activity expressed by OPAA-2, suggest that the OPAA-2 enzyme may, in nature, be used in peptide metabolism.

Purification and Properties of a Highly Active Organophosphorus Acid Anhydrolase from Alteromonas undina

A highly active organophosphorus acid anhydrolase from Alteromonas undina was purified to homogeneity and found to be composed of a single polypeptide chain with a molecular weight of 53,000. With diisopropylfluorophosphate as a substrate, the purified enzyme has a specific activity of ∼575 μmol/min/mg of protein. The enzyme has optimum activity at pH 8.0 and 55�C and is stimulated by sulfhydryl reducing agents and manganese. It is capable of rapidly hydrolyzing a wide range of nerve agents and several chromogenic phosphinates.

Characterization of organophosphorus hydrolases and the genetic manipulation of the phosphotriesterase from Pseudomonas diminuta

There are a variety of enzymes which are specifically capable of hydrolyzing organophosphorus esters with different phosphoryl bonds from the typical phosphotriester bonds of common insecticidal neurotoxins (e.g. paraoxon or coumaphos) to the phosphonate-fluoride bonds of chemical warfare agents (e.g. soman or sarin). These enzymes comprise a diverse set of enzymes whose basic architecture and substrate specificities vary dramatically, yet they appear to be ubiquitous throughout nature. The most thoroughly studied of these enzymes is the organophosphate hydrolase (opd gene product) of Pseudomonas diminuta and Flavobacterium sp. ATCC 27551, and the heterologous expression, post-translational modification, and genetic engineering studies undertaken with this enzyme are described.

Genetic and biochemical evidence for the lack of significant hydrolysis of soman by a Flavobacterium parathion hydrolase

Pure recombinant Flavobacterium parathion hydrolase (an organophosphorus acid anhydrase) from Streptomyces lividans was found to hydrolyze the toxic nerve agent soman at only 0.1% of the rate observed with parathion as substrate. Studies with wild-type and recombinant strains of S. lividans support the lack of significant soman breakdown by the hydrolase and also indicate the presence in S. lividans of other significant hydrolytic enzymatic activity towards soman.

Transfer and expression of an organophosphate insecticide-degrading gene from Pseudomonas in Drosophila melanogaster

The organophosphorus acid hydrolases represent a distinct class of enzymes that catalyze the hydrolysis of a variety of organophosphate substrates, including many insecticides and their structural analogues. The plasmid-borne opd gene of Pseudomonas diminuta strain MG specifies an organophosphorus acid hydrolase, a phosphotriesterase, that has been well characterized and can hydrolyze a broad spectrum of insect and mammalian neurotoxins. The in situ functioning of this enzyme in the metabolism of organophosphates has been analyzed directly in insects by transferring the opd gene into embryos of Drosophila melanogaster by P element-mediated transformation. The chromosomal locations of this stably inherited transgenic locus differed from strain to strain and demonstrated various expressivity on the whole-insect basis. Transcriptional induction of opd in one of these strains under control of the Drosophila heat shock promoter, hsp70, resulted in the synthesis of stable active enzyme that accumulated to high levels with repeated induction. The heat shock-induced synthesis of organophosphorus acid hydrolases in transgenic flies conferred enhanced resistance to toxic paralysis by the organophosphate insecticide paraoxon.

Inactivation of organophosphorus nerve agents by the phosphotriesterase from Pseudomonas diminuta

The phosphotriesterase from Pseudomonas diminuta was tested as a catalyst for the hydrolysis of phosphofluoridates. The purified enzyme has been shown to hydrolyze the phosphorus-fluorine bond of diisopropyl fluorophosphate, isopropyl methylphosphonofluoridate, and 1,2,2-trimethylpropylmethylphosphonofluoridate at pH 7.0, 25 degrees C, with turnover numbers of 41, 56, and 5 s-1, respectively. The enzymatic rate enhancement for the hydrolysis of sarin at pH 7.0 is 2.2 X 10(7). The turnover number for paraoxon hydrolysis is 2100 s-1. The enzyme does not hydrolyze methanesulfonyl fluoride, phenylmethylsulfonyl fluoride, or O-p-nitrophenyl phenylsulfonate nor do these compounds inactivate or inhibit the ability of the enzyme to hydrolyze diethyl p-nitrophenyl phosphate. The breadth of substrate utility and the efficiency of the hydrolytic reaction exceed the more limited abilities of other prokaryotic and eukaryotic enzymes that catalyze similar reactions. The substantial rate enhancement exhibited by this enzyme for the hydrolysis of a wide variety of organophosphorus nerve agents make this enzyme the prime candidate for the biological detoxification of insecticide and mammalian acetylcholinesterase inhibitors.

Dissimilar plasmids isolated from Pseudomonas diminuta MG and a Flavobacterium sp. (ATCC 27551) contain identical opd genes

The opd (organophosphate-degrading) gene derived from a 43-kilobase-pair plasmid (pSM55) of a Flavobacterium sp. (ATCC 27551) has a sequence identical to that of the plasmid-borne gene of Pseudomonas diminuta. Hybridization studies with DNA fragments obtained by restriction endonuclease digestion of plasmid DNAs demonstrated that the identical opd sequences were encoded on dissimilar plasmids from the two sources.

Cloning and sequencing of a plasmid-borne gene (opd) encoding a phosphotriesterase

Plasmid pCMS1 was isolated from Pseudomonas diminuta MG, a strain which constitutively hydrolyzes a broad spectrum of organophosphorus compounds. The native plasmid was restricted with PstI, and individual DNA fragments were subcloned into pBR322. A recombinant plasmid transformed into Escherichia coli possessed weak hydrolytic activity, and Southern blotting with the native plasmid DNA verified that the DNA sequence originated from pCMS1. When the cloned 1.3-kilobase fragment was placed behind the lacZ' promoter of M13mp10 and retransformed into E. coli, clear-plaque isolates with correctly sized inserts exhibited isopropyl-beta-D-thiogalactopyranoside-inducible whole-cell activity. Sequence determination of the M13 constructions identified an open reading frame of 975 bases preceded by a putative ribosome-binding site appropriately positioned upstream of the first ATG codon in the open reading frame. An intragenic fusion of the opd gene with the lacZ gene produced a hybrid polypeptide which was purified by beta-galactosidase immunoaffinity chromatography and used to confirm the open reading frame of opd. The gene product, an organophosphorus phosphotriesterase, would have a molecular weight of 35,418 if the presumed start site is correct. Eighty to ninety percent of the enzymatic activity was associated with the pseudomonad membrane fractions. When dissociated by treatment with 0.1% Triton and 1 M NaCl, the enzymatic activity was associated with a molecular weight of approximately 65,000, suggesting that the active enzyme was dimeric.