Purification and characterization of a carboxylesterase from Pseudomonas sp. KWI-56

Identification of lipolytic enzymes isolated from bacteria indigenous to Eucalyptus wood species for application in the pulping industry

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Phenol red screening plates is the best method for detecting lipolytic activity.

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Substrate specificity is affected by temperature and pH.

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Essential to test substrates at various pH and temperature to determine optima.

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Lipolytic enzymes indigenous to Eucalyptus sp. can assist in pitch control.

This study highlights the importance of determining substrate specificity at variable experimental conditions. Lipases and esterases were isolated from microorganisms cultivated from Eucalyptus wood species and then concentrated (cellulases removed) and characterized. Phenol red agar plates supplemented with 1% olive oil or tributyrin was ascertained to be the most favourable method of screening for lipolytic activity. Lipolytic activity of the various enzymes were highest at 45–61 U/ml at the optimum temperature and pH of between at 30–35 °C and pH 4–5, respectively. Change in pH influenced the substrate specificity of the enzymes tested. The majority of enzymes tested displayed a propensity for longer aliphatic acyl chains such as dodecanoate (C₁₂), myristate (C₁₄), palmitate (C₁₆) and stearate (C₁₈) indicating that they could be characterised as potential lipases. Prospective esterases were also detected with specificity towards acetate (C₂), butyrate (C₄) and valerate (C₅). Enzymes maintained up to 95% activity at the optimal pH and temperature for 2–3 h. It is essential to test substrates at various pH and temperature when determining optimum activity of lipolytic enzymes, a method rarely employed. The stability of the enzymes at acidic pH and moderate temperatures makes them excellent candidates for application in the treatment of pitch during acid bi-sulphite pulping, which would greatly benefit the pulp and paper industry.

Stereoselective esterase from Pseudomonas putida IFO12996 reveals alpha/beta hydrolase folds for D-beta-acetylthioisobutyric acid synthesis

Esterase (EST) from Pseudomonas putida IFO12996 catalyzes the stereoselective hydrolysis of methyl dl-beta-acetylthioisobutyrate (dl-MATI) to produce d-beta-acetylthioisobutyric acid (DAT), serving as a key intermediate for the synthesis of angiotensin-converting enzyme inhibitors. The EST gene was cloned and expressed in Escherichia coli; the recombinant protein is a non-disulfide-linked homotrimer with a monomer molecular weight of 33,000 in both solution and crystalline states, indicating that these ESTs function as trimers. EST hydrolyzed dl-MATI to produce DAT with a degree of conversion of 49.5% and an enantiomeric excess value of 97.2% at an optimum pH of about 8 to 10 and an optimum temperature of about 57 to 67 degrees C. The crystal structure of EST has been determined by X-ray diffraction to a resolution of 1.6 A, confirming that EST is a member of the alpha/beta hydrolase fold superfamily of enzymes and includes a catalytic triad of Ser97, Asp227, and His256. The active site is located approximately in the middle of the molecule at the end of a pocket approximately 12 A deep. EST can hydrolyze the methyl ester group without affecting the acetylthiol ester moiety in dl-MATI. The examination of substrate specificity of EST toward other linear esters revealed that the enzyme showed specific activity toward methyl esters and that it recognized the configuration at C-2.

Isolation, characterization, and heterologous expression of a carboxylesterase of Pseudomonas aeruginosa PAO1

We purified to homogeneity an intracellular esterase from the opportunistic pathogen Pseudomonas aeruginosa PAO1. The enzyme hydrolyzes p-nitrophenyl acetate and other acetylated substrates. The N-terminal amino acid sequence was analyzed and 11 residues, SEPLILDAPNA, were determined. The corresponding gene PA3859 was identified in the P. aeruginosa PAO1 genome as the only gene encoding for a protein with this N-terminus. The encoding gene was cloned in Escherichia coli, and the recombinant protein expressed and purified to homogeneity. According to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis and analytical gel filtration chromatography, the esterase was found to be a monomer of approximately 24 kDa. The experimentally determined isoelectric point was 5.2 and the optimal enzyme activity was at 55 degrees C and at pH 9.0. The esterase preferentially hydrolyzed short-chain fatty acids. It is inhibited by phenylmethylsulfonyl fluoride (PMSF) but not by ethylendiaminotetraacetic acid (EDTA). Native enzyme preparations typically showed a Michaelis constant (K(m)) and V(max) of 0.43 mM and 12,500 U mg(-1), respectively, using p-nitrophenyl acetate as substrate. Homology-based database searches clearly revealed the presence of the consensus GXSXG signature motif that is present in the serine-dependent acylhydrolase protein family.

Hydrophobilization of esterase by genetic combination with polyproline or polytyrosine at the carboxyl terminal

Polyproline (Poly-Pro) that is an amphiphilic polypeptide, or polytyrosine (Poly-Tyr) that is a hydrophobic polypeptide, were connected to the carboxy terminus of Pseudomonas sp. esterase by the recombinant DNA technique. The hydrophobicity of the esterase was enhanced by the introduction of Poly-Pro or Poly-Tyr, and also by increasing chain length of the polypeptides. Poly-Tyr increased the hydrophobicity of esterase more than Poly-Pro. Poly-Tyr induced significant conformational change of fusion esterase, but Poly-Pro did not. Consequently, the introduction of Poly-Tyr led to loss of activity of the fusion enzyme to a negligible level. On the other hand, the Poly-Pro-fusion-esterase retained enzymatic activity and the hydrolytic activity (kcat/Km) of the fusion esterase carrying 40 proline residues (esterase-Pro40) relative to that of the wild-type esterase with the substrates p-nitrophenyl-propionate, -pentanoate, and -hexanoate was 1.76, 1.95, and 4.7, respectively. The results could be explained in terms of easier access of long-chain carboxylate to the fusion esterase compared to the wild-type esterase in aqueous solution.

Hydrophobilization of an esterase by genetic combination with polyproline at the carboxyl terminal

Polyproline, which is an amphiphilic polypeptide, was incorporated into the carboxyl terminal of an esterase by the recombinant DNA technique. The hydrophobicity of the esterase increased with increasing chain length of polyproline without inducing significant conformational changes. The mutant esterase catalyzed the hydrolysis of long-chain carboxylic acid ester more efficiently than the native esterase. It is considered that the alteration of substrate specificity is due to enhanced access of the mutant esterases to hydrophobic substrates. Copyright 1998 John Wiley & Sons, Inc.