Thermal inactivation of a recombinant lipoxygenase from Pseudomonas aeruginosa BBE in the absence and presence of additives

Consensus design for improved thermostability of lipoxygenase from Anabaena sp. PCC 7120

Background

Lipoxygenase (LOX) from Anabaena sp. PCC 7120 (Ana-rLOX) offers important applications in the food industry, especially for improving aroma and dough rheological properties. However, industrial applications of LOXs have been limited by their poor thermostability. Herein, we report a bioinformatics-based consensus concept approach for the engineering of thermostable Ana-rLOX.

Results

A series of mutations (N130D, G260A, S437T, N130D/G260Q, N130D/S437Y) showed higher thermostability and activity than the wild-type enzyme. Thus, N130D/G260Q exhibited a 6.6-fold increase in half-life and 2.45 °C increase in unfolding temperature; N130D/S437Y showed a 10 °C increase in optimal temperature. The secondary structure did not change much that contributed to improved thermostability were investigated in detail using circular dichroism. Homology modeling suggested that enhanced thermostability and specific activity may result from favorable hydrophobic interactions.

Conclusions

A series of mutations were achieved, showing higher thermostability and activity than the wild-type enzyme by semi-rational mutagenesis with limited structure information. Our findings provide important new insights into molecular modifications aimed at improving Ana-rLOX thermostability and activity.

Electronic supplementary material

The online version of this article (10.1186/s12896-018-0468-4) contains supplementary material, which is available to authorized users.

Improvement of enzymatic properties of Rhizopus oryzae α-amylase by site-saturation mutagenesis of histidine 286

Optimal pH and ideal functioning temperature for fungal α-amylase can greatly contribute to improving enzyme efficiency in maltose-forming ability. This work aimed to improve the enzymatic properties of Rhizopus oryzae α-amylase by site-saturation mutagenesis of histidine 286. The biochemical properties of selected mutant enzymes were modified to increase their enzymatic efficiencies compared to their wild-type counterparts. For instance, the optimum temperature of mutants H286 L, H286I, H286S and H286 T was increased from 50 °C to 55 °C, while a similar increase was observed for H286 P from 50 °C to 60 °C. The optimum pH of mutants H286 L, H286I and H286D shifted from 5.5 to 5.0, and the optimum pH of mutant H286E shifted from 5.5 to 4.5. The results obtained showed that the mutant H286I showed a 1.5-fold increase in half-life at 55 °C and the mutant H286E showed a 6.43-fold increase in half-life at a pH of 4.5. Furthermore, the ability to form maltose from soluble starch for mutants H286 L and H286 M was significantly improved under the optimum conditions determined in the study. The catalytic mechanism responsible for improved maltose-forming ability was confirmed through molecular docking simulations with maltotriose among wild-type and mutant enzymes. The mutants with improved enzymatic properties that were attained in this work may help in future computer-aided directed evolution of fungal α-amylase.

Preparation of Stable Cross-Linked Enzyme Aggregates (CLEAs) of a Ureibacillus thermosphaericus Esterase for Application in Malathion Removal from Wastewater

In this study, the active and stable cross-linked enzyme aggregates (CLEAs) of the thermostable esterase estUT1 of the bacterium Ureibacillus thermosphaericus were prepared for application in malathion removal from municipal wastewater. Co-expression of esterase with an E. coli chaperone team (KJE, ClpB, and ELS) increased the activity of the soluble enzyme fraction up to 200.7 ± 15.5 U mg−1. Response surface methodology (RSM) was used to optimize the preparation of the CLEA-estUT1 biocatalyst to maximize its activity and minimize enzyme loss. CLEA-estUT1 with the highest activity of 29.4 ± 0.5 U mg−1 (90.6 ± 2.7% of the recovered activity) was prepared with 65.1% (w/v) ammonium sulfate, 120.6 mM glutaraldehyde, and 0.2 mM bovine serum albumin at 5.1 h of cross-linking. The biocatalyst has maximal activity at 80 °С and pH 8.0. Analysis of the properties of CLEA-estUT1 and free enzyme at 50–80 °C and pH 5.0–10.0 showed higher stability of the biocatalyst. CLEA-estUT1 showed marked tolerance against a number of chemicals and high operational stability and activity in the reaction of malathion hydrolysis in wastewater (up to 99.5 ± 1.4%). After 25 cycles of malathion hydrolysis at 37 °С, it retained 55.2 ± 1.1% of the initial activity. The high stability and reusability of CLEA-estUT1 make it applicable for the degradation of insecticides.

Secreted lipoxygenase from Pseudomonas aeruginosa exhibits biomembrane oxygenase activity and induces hemolysis in human red blood cells

Pseudomonas aeruginosa (PA) expresses a secreted lipoxygenase (LOX), which oxygenates free arachidonic acid predominantly to 15S-H(p)ETE. The enzyme is capable of binding phospholipids at its active site and physically interacts with model membranes. However, its membrane oxygenase activity has not been quantified. To address this question, we overexpressed PA-LOX as intracellular his-tag fusion protein in Escherichia coli, purified it to electrophoretic homogeneity and compared its biomembrane oxygenase activity with that of rabbit ALOX15. We found that both enzymes were capable of oxygenating mitochondrial membranes to specific oxygenation products and 13S-H(p)ODE and 15S-H(p)ETE esterified to phosphatidylcholine and phosphatidylethanolamine were identified as major oxygenation products. When normalized to similar linoleic acid oxygenase activity, the rabbit enzyme exhibited a much more effective mitochondrial membrane oxygenase activity. In contrast, during long-term incubations (24 h) with red blood cells PA-LOX induced significant (50%) hemolysis whereas rabbit ALOX15 was more or less ineffective. These data indicate the principle capability of PA-LOX of oxygenating membrane bound phospholipids which is likely to alter the barrier function of the biomembranes. Although the membrane oxygenase activity was lower than the fatty acid oxygenase activity of PA-LOX red blood cell membrane oxygenation might be of biological relevance for P. aeruginosa septicemia.

Overproduction of pro-transglutaminase from Streptomyces hygroscopicus in Yarrowia lipolytica and its biochemical characterization

Background

Transglutaminases (TGase), synthesized as a zymogen (pro-TGase) in Streptomyces sp., are important enzymes in food industry. Due to the important applications of TGase in food industry, obtaining robust and food-safe TGase-producing strains has attracted much attention during the past decade. In this study, Streptomyces hygroscopicus pro-TGase was efficiently expressed and secreted by a food-grade host, Yarrowia lipolytica, without antibiotic markers.

Results

The pro-TGase gene was cloned into integrative vectors pINA1296 (monocopy) and pINA1297 (multicopy), and was used to transform the Y. lipolytica Po1g or Po1h strain, respectively. Expression was driven by a recombinant hp4d promoter and secretion obtained using a XPR2 pre-sequence as a signal peptide. The highest yield of extracellular pro-TGase produced by the recombinant Po1h strain corresponded to 5.3 U/mL of TGase, a level 8.8 fold higher than that obtained using the recombinant Po1g strain. Asparagines in two potential Asn-linked glycosylation sites (Asn160 and Asn355) from pro-TGase were mutated to glutamine individually or simultaneously, yielding the deglycosylated variants N160Q, N355Q, and N160Q/N355Q. The activities of N160Q, N355Q and N160Q/N355Q constructs were respectively 5.3 U/mL, 7.8 U/mL, and 3.0 U/mL, equivalent to 100 %, 147 %, and 57 % of that from wild-type pro-TGase. The TGase yield of N355Q variant was raised to 35.3 U/mL of by using a glycerol feeding strategy in a 3 L fermenter. The optimal pH and temperature of the activated pro-TGase, and of its deglycosylated variants, were in the range of 5.0-6.0 pH and 40-45 °C, respectively. The half-life of the recombinant wild-type pro-TGase at 37 °C reached 34.0 min, and those of the variants were from 24.2 min to 11.5 min. In contrast to the wild-type pro-TGase, all of the variants had decreased specific activities, and both the K_m and k_cat values of the variants decreased accordingly.

Conclusions

This study constitutes the first report of the heterologous expression of a pro-TGase in Y. lipolytica, and provides new possibilities for the efficient production of TGases used in food processing.