Expression and Characterization of a New Thermostable Esterase from Clostridium thermocellum

Identification and Biochemical Characterization of a Novel Hormone-Sensitive Lipase Family Esterase Est19 from the Antarctic Bacterium Pseudomonas sp. E2-15

Esterases represent an important class of enzymes with a wide variety of industrial applications. A novel hormone-sensitive lipase (HSL) family esterase, Est19, from the Antarctic bacterium Pseudomonas sp. E2-15 is identified, cloned, and expressed. The enzyme possesses a GESAG motif containing an active serine (S) located within a highly conserved catalytic triad of Ser155, Asp253, and His282 residues. The catalytic efficiency (kcat/Km) of Est19 for the pNPC6 substrate is 148.68 s-1mM-1 at 40 °C. Replacing Glu154 juxtaposed to the critical catalytic serine with Asp (E154→D substitution) reduced the activity and catalytic efficiency of the enzyme two-fold, with little change in the substrate affinity. The wild-type enzyme retained near complete activity over a temperature range of 10-60 °C, while ~50% of its activity was retained at 0 °C. A phylogenetic analysis suggested that Est19 and its homologs may represent a new subfamily of HSL. The thermal stability and stereo-specificity suggest that the Est19 esterase may be useful for cold and chiral catalyses.

Characterization of a novel hyper-thermostable and chlorpyrifos-hydrolyzing carboxylesterase EstC: A representative of the new esterase family XIX

Carboxylesterases have widely been used in a series of industrial applications, especially, the detoxification of pesticide residues. In the present study, EstC, a novel carboxylesterase from Streptomyces lividans TK24, was successfully heterogeneously expressed, purified and characterized. Phylogenetic analysis showed that EstC can be assigned as the first member of a novel family XIX. Multiple sequence alignment indicated that EstC has highly conserved structural features, including a catalytic triad formed by Ser155, Asp248 and His278, as well as a canonical Gly-His-Ser-Ala-Gly pentapeptide. Biochemical characterization indicated that EstC exhibited maximal activity at pH 9.0 (Tris-HCl buffer) and 55 °C. It also showed higher activity towards short-chain substrates, with the highest activity for p-nitrophenyl acetate (pNPA2) (K_m = 0.31 ± 0.02 mM, k_cat/K_m = 1923.35 ± 9.62 s^-1 mM^-1) compared to other pNP esters used in this experiment. Notably, EstC showed hyper-thermostability and good alkali stability. The activity of EstC had no significant changes when it was incubated under 55 °C for 100 h and reached half-life after incubation at 100 °C for 8 h. Beyond that, EstC also showed stability at pH ranging from 6.0 to 11.0 and about 90% residual activity still reserved after treatment at pH 8.0 or 9.0 for 26 h, especially. Furthermore, EstC had outstanding potential for bioremediation of chlorpyrifos-contaminated environment. The recombinant enzyme (0.5 U mL^-1) could hydrolyze 79.89% chlorpyrifos (5 mg L^-1) at 37 °C within 80 min. These properties will make EstC have a potential application value in various industrial productions and detoxification of chlorpyrifos residues.

Identification and characterization of a novel bacterial carbohydrate esterase from the bacterium Pantoea ananatis Sd-1 with potential for degradation of lignocellulose and pesticides

OBJECTIVE

Identification and characterization of a novel bacterial carbohydrate esterase (PaCes7) with application potential for lignocellulose and pesticide degradation.

RESULTS

PaCes7 was identified from the lignocellulolytic bacterium, Pantoea ananatis Sd-1 as a new carbohydrate esterase. Recombinant PaCes7 heterologously expressed in Escherichia coli showed a clear preference for esters with short-chain fatty acids and exhibited maximum activity towards α-naphthol acetate at 37 °C and pH 7.5. Purified PaCes7 exhibited its catalytic activity under mesophilic conditions and retained more than 40% activity below 30 °C. It displayed a relatively wide pH stability from pH 6-11. Furthermore, the enzyme was strongly resistant to Mg²⁺, Pb²⁺, and Co²⁺ and activated by K⁺ and Ca²⁺. Both P. ananatis Sd-1 and PaCes7 could degrade the pesticide carbaryl. Additionally, PaCes7 was shown to work in combination with cellulase and/or xylanase in rice straw degradation.

CONCLUSIONS

The data suggest that PaCes7 possesses promising biotechnological potential.

Characterization of a novel thermostable carboxylesterase from thermoalkaliphilic bacterium Bacillus thermocloaceae

A novel thermostable carboxylesterase (Est5250) of thermoalkaliphilic bacterium Bacillus thermocloaceae was heterologously expressed in Escherichia coli and its biochemical properties were investigated. Est5250 showed optimum esterase activity at 60 °C and pH 8.0. The enzyme was highly thermostable at 60 °C, interestingly, the thermostability was enhanced in the presence of Ca²⁺, retaining more than 60% of its original activity after 12 h of pre-incubation. Est5250 was active in the presence of 1% (v/v) of organic solvents and 0.1% (v/v) of non-ionic detergents. The enzyme activity was significantly enhanced up to 167% and 159% in the presence of 2-mercaptoethanol and dithiothreitol, respectively. Est5250 showed high substrate specificity for short-chain p-nitrophenyl-esters. Kinetic constants, K_m and k_cat, for p-nitrophenyl-acetate were 185.8 μM and 186.6 s^-1, respectively. Est5250 showed outstanding thermostability and tolerance to various organic solvents under thermoalkaliphilic conditions, suggesting that it would be a highly suitable biocatalyst for various biotechnological applications. Abbreviations: B. thermocloaceae sp.: Bacillus thermocloaceae; E. coli: Escherichia coli; NP: nitrophenyl; DMSO: dimethyl sulfoxide; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; DMF: dimethyl formamide; EGTA: ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid; CTAB: cetrimonium bromide; PMSF: phenylmethylsulfonyl fluoride; DEPC: diethyl pyrocarbonate; 2-ME: 2-mercaptoethanol; DTT: dithiothreitol.