Isolation and partial characterization of a novel thermostable carboxylesterase from a thermophilic Bacillus

Esterase is a powerful tool for the biodegradation of pyrethroid insecticides

Agricultural and household applications of pyrethroid insecticides have significantly increased residual concentrations in living cells and environments. The enhanced concentration is toxic for living beings. Pyrethroid hydrolase enzyme (pyrethroid catalyzing esterase) regulates pyrethroid degradation, and has been well reported in various organisms (bacteria, fungi, insects and animals). Hydrolysis mechanisms of these esterases are different from others and properly function at factors viz., optimum temperature, pH and physicochemical environment. Active site of the enzyme contains common amino acids that play important role in pyrethroid catalysis. Immobilization technology emphasizes the development of better reusable efficiency of pyrethroid hydrolases to carry out large-scale applications for complete degradation of pyrethroids from the environments. In this review we have attempted to provide insights of pyrethroid-degrading esterases in different living systems along with complete mechanisms.

Molecular cloning, over expression and characterization of thermoalkalophilic esterases isolated from Geobacillus sp

Due to potential use for variety of biotechnological applications, genes encoding thermoalkalophilic esterase from three different Geobacillus strains isolated from thermal environmental samples in Balçova (Agamemnon) geothermal site were cloned and respective proteins were expressed in Escherichia coli (E.coli) and characterized in detail. Three esterases (Est1, Est2, Est3) were cloned directly by PCR amplification using consensus degenerate primers from genomic DNA of the strains Est1, Est2 and Est3 which were from mud, reinjection water and uncontrolled thermal leak, respectively. The genes contained an open reading frame (ORF) consisting of 741 bp for Est1 and Est2, which encoded 246 amino acids and ORF of Est3 was 729 bp encoded 242 amino acids. The esterase genes were expressed in E. coli and purified using His-Select HF nickel affinity gel. The molecular mass of the recombinant enzyme for each esterase was approximately 27.5 kDa. The three esterases showed high specific activity toward short chain p-NP esters. Recombinant Est1, Est2, Est3 have exhibited similar activity and the highest esterase activity of 1,100 U/mg with p-nitrophenyl acetate (pNPC(2)) as substrate was observed with Est1. All three esterase were most active around 65°C and pH 9.5-10.0. The effect of organic solvents, several metal ions, inhibitors and detergents on enzyme activity for purified Est1, Est2, Est3 were determined separately and compared.

The enzymes from extreme thermophiles: bacterial sources, thermostabilities and industrial relevance

This review on enzymes from extreme thermophiles (optimum growth temperature greater than 65 degrees C) concentrates on their characteristics, especially thermostabilities, and their commercial applicability. The enzymes are considered in general terms first, with comments on denaturation, stabilization and industrial processes. Discussion of the enzymes subsequently proceeds in order of their E.C. classification: oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases. The ramifications of cloned enzymes from extreme thermophiles are also discussed.

A snapshot of a transition state analogue of a novel thermophilic esterase belonging to the subfamily of mammalian hormone-sensitive lipase

EST2 is a novel thermophilic carboxylesterase, isolated and cloned from Alicyclobacillus (formerly Bacillus) acidocaldarius, which optimally hydrolyses esters with acyl chain lengths of six to eight carbon atoms at 70 degrees C. On the basis of the amino acid sequence homology, it has been classified as a member of the mammalian hormone-sensitive lipase (HSL) subfamily. The crystal structure of EST2, complexed with a sulphonyl derivative, has been determined at 2.6 A resolution by a multiple wavelength anomalous diffraction experiment on a seleno-methionine derivative. EST2 presents a canonical alpha/beta hydrolase core, shielded at the C-terminal side by a cap region built up of five helices. It contains the lipase-like catalytic triad, Ser155, His282 and Asp252, whereby the nucleophile is covalently modified. This allows an unambiguous view of the putative active site of EST2, detecting the oxyanion hole, in whose formation the amino acid sequence motif His81-Gly82-Gly83-Gly84 is involved, and the hydrophobic binding pocket for the acyl chain. The structural model here reported provides the first example of a transition state analogue of an esterase/lipase belonging to the HSL group, thus affording useful information for the design of medical inhibitors. Moreover, as the first X-ray structure of a thermophilic carboxylesterase, the comparison with its mesophilic homologue, the Brefeldin A esterase (BFAE) from Bacillus subtilis, allows the identification of putative determinants of thermal stability.

Cloning, overexpression, and properties of a new thermophilic and thermostable esterase with sequence similarity to hormone-sensitive lipase subfamily from the archaeon Archaeoglobus fulgidus

A new esterase gene from the hyperthermophilic archaeon Archaeoglobus fulgidus, reported to show homology with the mammalian hormone-sensitive lipase (HSL)-like group of the esterase/lipase family, was cloned by means of the polymerase chain reaction from the A. fulgidus genome. In order to compare the biochemical properties of this putative hyperthermophilic enzyme with those of the homologous, thermophilic member of HSL group, namely Alicyclobacillus (formerly Bacillus) acidocaldarius esterase 2 (EST2), an overexpression system in Escherichia coli was established. The recombinant protein, expressed in soluble and active form at 20 mg/liter of E. coli culture, was purified to homogeneity and characterized. The enzyme, a 35.5-kDa monomeric protein, was demonstrated to be a B"-type carboxylesterase (EC 3.1.1.1) on the basis of substrate specificity and the action of inhibitors. Among the p-nitrophenyl (PNP) esters tested the best substrate was PNP-hexanoate with K(m) and k(cat) values of 11 +/- 3 microM (mean +/- SD, n = 3) and 1014 +/- 38 s(-1) (mean +/- SD, n = 3), respectively, at 70 degrees C and pH 7.1. Inactivation by diethylpyrocarbonate, phenylmethylsulfonylfluoride, diisopropylfosfofluoridate (DFP), and physostigmine, as well as labeling with [(3)H]DFP, supported our previous suggestion of a catalytic triad made up of Ser(160)-His(285)-Asp(255). The sequence identity with the thermostable A. acidocaldarius EST2 was 42.5%. The enzyme proved to be much more stable than its Alicyclobacillus counterpart. The conformational dynamics of the two proteins were investigated by frequency-domain fluorometry and anisotropy decay and the activity/stability/temperature relationship was discussed.

Purification and partial characterization of a novel thermophilic carboxylesterase with high mesophilic specific activity

An esterase activity obtained from a strain of Bacillus stearothermophilus was purified 5,133-fold to electrophoretic homogeneity with 26% recovery. The purified esterase had a specific activity of 2,032 mumol min-1 mg-1 based on the hydrolysis of p-nitrophenyl caproate at pH 7.0 and 30 degrees C. The apparent molecular mass was 50,000 +/- 2,000 daltons from sodium dodecyl sulfate-polyacrylamide gel electrophoresis and 45,000 +/- 3,000 daltons from gel filtration. Native polyacrylamide gels stained for esterase activity showed three bands. The isoelectric points were estimated to be 5.7, 5.8, and 6.0. Forty amino acid residues were sequenced at the N-terminus. The sequence showed no degeneracy, suggesting that the three esterases are functionally identical carboxylesterases differing by a limited number of amino acids. The enzyme showed maximum activity at pH 7.0 and was very stable at pH 6.0-8.9 with optimum stability at pH 6.0. At this pH and 60 degrees C the half-life was 170 h. Esterase activity was totally inhibited by phenylmethanesulfonyl fluoride, parahydroxymercuribenzoate, eserine, and tosyl-L-phenylalanine, but not by ethylendiaminetetra acetic acid. The esterase obeyed Michaelis-Menten kinetics in the hydrolysis of p-nitrophenyl esters, but both Vmax and KM were protein concentration-dependent. The esterase was able to hydrolyse a number of p-nitrophenyl derivatives (amino acid derivatives and aliphatic acids with different chain lengths).

Purification and characterization of a thermostable carboxylesterase from the thermoacidophilic eubacterium Bacillus acidocaldarius

A thermostable carboxylesterase from the thermoacidophilic eubacterium Bacillus acidocaldarius was isolated, purified 1800-fold to homogeneity, and characterised. The apparent molecular mass was 36.5 +/- 2.5 kDa when determined by SDS/PAGE and 37.5 kDa when determined by analytical gel filtration, suggesting a monomeric structure. The pure enzyme regained activity on removal of SDS after SDS/PAGE. Several esterase activities were revealed in crude extracts by PAGE and activity staining, although only one was detected after SDS/PAGE and detergent removal. The esterase showed optimal activity at around 70 degrees C and pH 8, and was thermostable. p-Nitrophenyl esters of fatty acids from C2 to C12 were used as substrates; Vmax and Km values were determined at three different temperatures. The enzyme was able to hydrolyse tributyrylglycerol and trihexanoyl-glycerol dissolved in 0.8% acetonitrile, but neither lipase activity toward [14C]trioleoylglycerol nor proteolytic activity could be detected. Inactivation by diethyl p-nitrophenyl phosphate, by phenyl-methansulfonyl fluoride and physostigmine, and by diethylpyrocarbonate suggested that the enzyme contained a catalytic triad Ser-His-Asp/Glu in the active site, similar to that demonstrated for other serine-type enzymes. The amino acid composition and the sequence of 19 amino acid residues at the N-terminus were determined. These data, together with substrate preference and inhibition pattern, allowed us to classify this enzyme as a B-type carboxylesterase (EC 3.1.1.1).

Transformation of synthetic pyrethroid insecticides by a thermophilic Bacillus sp

Employing a mineral salts medium containing Tween 80 as the primary carbon source, a strain of Bacillus stearothermophilus was isolated which was able to hydrolyse selected second and third-generation pyrethroids to non-insecticidal products. Of a range of pyrethroid insecticides the trans-isomer of permethrin was the most readily transformed by this microbial isolate, whilst flumethrin was the least. 3-Phenoxybenzoic acid and the respective halovinyl or haloacid moieties were detected as the major hydrolytic products of the pyrethroids. It is believed that 3-phenoxybenzoic acid was formed from 3-phenoxybenzyl alcohol which was not however detected as an intermediate in these systems. 3-Phenoxybenzoic acid was further transformed to 4-hydroxy-3-phenoxybenzoic acid. A potential metabolic pathway has been described.