Enhancement of the enzymatic activity of Escherichia coli acetyl esterase by random mutagenesis

Effect of Cysteine Residue Substitution in the GCSAG Motif of the PMGL2 Esterase Active Site on the Enzyme Properties

The gene coding for PMGL2 esterase, which belongs to the family of mammalian hormone-sensitive lipases (HSLs), was discovered by screening a metagenomic DNA library from a permafrost soil. The active site of PMGL2 contains conserved GXSXG motif which includes Cys173 residue next to the catalytic Ser174. In order to clarify the functional role of the cysteine residue in the GCSAG motif, we constructed a number of PMGL2 mutants with Cys173 substitutions and studied their properties. The specific activity of the C173D mutant exceeded the specific activity of the wild-type enzyme (wtPMGL2) by 60%, while the C173T/C202S mutant displayed reduced catalytic activity. The activity of the C173D mutant with p-nitrophenyl octanoate was 15% higher, while the activity of the C173T/C202S mutant was 17% lower compared to wtPMGL2. The C173D mutant was also characterized by a high activity at low temperatures (20-35°C) and significant loss of thermal stability. The k_cat value for this protein was 56% higher than for the wild-type enzyme. The catalytic constants of the C173S mutant were close to those of wtPMGL2; this enzyme also demonstrated the highest thermal stability among the studied mutants. The obtained results demonstrate that substitutions of amino acid residues adjacent to the catalytic serine residue in the GXSXG motif can have a significant effect on the properties of PMGL2 esterase.

Main Structural Targets for Engineering Lipase Substrate Specificity

Microbial lipases represent one of the most important groups of biotechnological biocatalysts. However, the high-level production of lipases requires an understanding of the molecular mechanisms of gene expression, folding, and secretion processes. Stable, selective, and productive lipase is essential for modern chemical industries, as most lipases cannot work in different process conditions. However, the screening and isolation of a new lipase with desired and specific properties would be time consuming, and costly, so researchers typically modify an available lipase with a certain potential for minimizing cost. Improving enzyme properties is associated with altering the enzymatic structure by changing one or several amino acids in the protein sequence. This review detailed the main sources, classification, structural properties, and mutagenic approaches, such as rational design (site direct mutagenesis, iterative saturation mutagenesis) and direct evolution (error prone PCR, DNA shuffling), for achieving modification goals. Here, both techniques were reviewed, with different results for lipase engineering, with a particular focus on improving or changing lipase specificity. Changing the amino acid sequences of the binding pocket or lid region of the lipase led to remarkable enzyme substrate specificity and enantioselectivity improvement. Site-directed mutagenesis is one of the appropriate methods to alter the enzyme sequence, as compared to random mutagenesis, such as error-prone PCR. This contribution has summarized and evaluated several experimental studies on modifying the substrate specificity of lipases.

A novel cold-adapted esterase from Enterobacter cloacae: Characterization and improvement of its activity and thermostability via the site of Tyr193Cys

Background

In industries lipolytic reactions occur in insensitive conditions such as high temperature thus novel stout esterases with unique properties are attracts to the industrial application. Protein engineering is the tool to obtain desirable characters of enzymes. A novel esterase gene was isolated from South China Sea and subjected to a random mutagenesis and site directed mutagenesis for higher activity and thermo-stability compared to wild type.

Results

A novel esterase showed the highest hydrolytic activity against p-nitrophenyl acetate (pNPA, C2) and the optimal activity at 40 °C and pH 8.5. It was a cold-adapted enzyme and retained approximately 40% of its maximum activity at 0 °C. A mutant, with higher activity and thermo-stability was obtained by random mutagenesis. Kinetic analysis indicated that the mutant Val29Ala/Tyr193Cys shown 43.5% decrease in K_m, 2.6-fold increase in K_cat, and 4.7-fold increase in K_cat/K_m relative to the wild type. Single mutants V29A and Y193C were constructed and their kinetic parameters were measured. The results showed that the values of K_m, K_cat, and K_cat/K_m of V29A were similar to those of the wild type while Y193C showed 52.7% decrease in K_m, 2.7-fold increase in K_cat, and 5.6-fold increase in K_cat/K_m compared with the wild type. The 3-D structure and docking analysis revealed that the replacement of Tyr by Cys could enlarge the binding pocket. Moreover Y193C also showed a better thermo-stability for the reason its higher hydrophobicity and retained 67% relative activity after incubation for 3 h at 50 °C.

Conclusions

The superior quality of modified esterase suggested it has great potential application in extreme conditions and the mutational work recommended that important information for the study of esterase structure and function.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-0885-z) contains supplementary material, which is available to authorized users.

Mutagenesis for improvement of activity and thermostability of amylomaltase from Corynebacterium glutamicum

This work aims to improve thermostability of amylomaltase from a mesophilic Corynebacterium glutamicum (CgAM) by random and site-directed mutagenesis. From error prone PCR, a mutated CgAM with higher thermostability at 50 °C compared to the wild-type was selected and sequenced. The result showed that the mutant contains a single mutation of A406V. Site-directed mutagenesis was then performed to construct A406V and A406L. Both mutated CgAMs showed higher intermolecular transglucosylation activity with an upward shift in the optimum temperature and a slight increase in the optimum pH for disproportionation and cyclization reactions. Thermostability of both mutated CgAMs at 35-40 °C was significantly increased with a higher peak temperature from DSC spectra when compared to the wild-type. A406V had a greater effect on activity and thermostability than A406L. The catalytic efficiency values kcat/Km of A406V- and A406L-CgAMs were 2.9 and 1.4 times higher than that of the wild-type, respectively, mainly due to a significant increase in kcat. LR-CD product analysis demonstrated that A406V gave higher product yield, especially at longer incubation time and higher temperature, in comparison to the wild-type enzyme.

Enantioselectivity and catalysis improvements of Pseudomonas cepacia lipase with Tyr and Asp modification

A concise strategy to improve the p-nitrophenyl palmitate catalytic activity and enantioselectivity towards secondary alcohols of PcL is described.