Activity enhancement of Trametes versicolor aflatoxin B1-degrading enzyme (TV-AFB1D) by molecular docking and site-directed mutagenesis techniques

Rational Design for Enhancing Cellobiose Dehydrogenase Activity and Its Synergistic Role in Straw Degradation

Addressing the demand for efficient biological degradation of straw, this study employed rational design coupled with structural biology and enzyme engineering techniques to enhance the catalytic activity of cellobiose dehydrogenase (PsCDH, CDH form Pycnoporus sanguineus). By predicting and modifying the active site and key amino acids of PsCDH, several CDH immobilized enzyme preparations with higher catalytic activities were successfully obtained. The excellent mutant T1 (C286Y/A461H/F464R) exhibited a 2.7-fold increase in enzyme activity compared to the wild type. Simulated calculations indicated that the enhancement of catalytic activity was primarily due to the formation of additional intermolecular interactions between CDH and the substrate, as well as the enlargement of the substrate pocket to reduce steric hindrance effects. Additionally, molecular dynamics simulation analysis revealed a potential correlation between structural stability and enzyme activity. When PsCDH was added to a multienzyme synergistic straw degradation system, the cellulose degradation rate increased by 1.84-fold. Moreover, mutant T1 further increased the degradation of lignocellulose in the mixed system. This study provides efficient enzyme sources and modification strategies for the high-efficiency biological conversion of straw and unconventional feedstock degradation, thereby possessing significant academic value and application prospects.

Characterization, Mechanism, and Application of Dipeptidyl Peptidase III: An Aflatoxin B1-Degrading Enzyme from Aspergillus terreus HNGD-TM15

Aflatoxin B1 is a notorious mycotoxin with mutagenicity and carcinogenicity, posing a serious hazard to human and animal health. In this study, an AFB1-degrading dipeptidyl-peptidase III mining from Aspergillus terreus HNGD-TM15 (ADPP III) with a molecular weight of 79 kDa was identified. ADPP III exhibited optimal activity toward AFB1 at 40 °C and pH 7.0, maintaining over 80% relative activity at 80 °C. The key amino acid residues that affected enzyme activity were identified as H450, E451, H455, and E509 via bioinformatic analysis and site-directed mutagenesis. The degradation product of ADPP III toward AFB1 was verified to be AFD1. The zebrafish hepatotoxicity assay verified the toxicity of the AFB1 degradation product was significantly weaker than that of AFB1. The result of this study proved that ADPP III presented a promising prospect for industrial application in food and feed detoxification.

Combined Strategies for Improving Aflatoxin B1 Degradation Ability and Yield of a Bacillus licheniformis CotA-Laccase

Aflatoxin B1 (AFB1) contamination is a serious threat to nutritional safety and public health. The CotA-laccase from Bacillus licheniformis ANSB821 previously reported by our laboratory showed great potential to degrade AFB1 without redox mediators. However, the use of this CotA-laccase to remove AFB1 in animal feed is limited because of its low catalytic efficiency and low expression level. In order to make better use of this excellent enzyme to effectively degrade AFB1, twelve mutants of CotA-laccase were constructed by site-directed mutagenesis. Among these mutants, E186A and E186R showed the best degradation ability of AFB1, with degradation ratios of 82.2% and 91.8% within 12 h, which were 1.6- and 1.8-times higher than those of the wild-type CotA-laccase, respectively. The catalytic efficiencies (kcat/Km) of E186A and E186R were found to be 1.8- and 3.2-times higher, respectively, than those of the wild-type CotA-laccase. Then the expression vectors pPICZαA-N-E186A and pPICZαA-N-E186R with an optimized signal peptide were constructed and transformed into Pichia pastoris GS115. The optimized signal peptide improved the secretory expressions of E186A and E186R in P. pastoris GS115. Collectively, the current study provided ideal candidate CotA-laccase mutants for AFB1 detoxification in food and animal feed and a feasible protocol, which was desperately needed for the industrial production of CotA-laccases.

Metabolites and degradation pathways of microbial detoxification of aflatoxins: a review

The degradation of aflatoxins using nonpathogenic microbes and their enzymes is emerging as a safe and economical alternative to chemical and physical methods for the detoxification of aflatoxins in food and feeds. Many bacteria and fungi have been identified as aflatoxin degraders. This review is focused on the chemical identification of microbial degradation products and their degradation pathways. The microbial degradations of aflatoxins are initiated by oxidation, hydroxylation, reduction, or elimination reactions mostly catalyzed by various enzymes belonging to the classes of laccase, reductases, and peroxidases. The resulting products with lesser chemical stability further undergo various reactions to form low molecular weight products. Studies on the chemical and biological nature of degraded products of aflatoxins are necessary to ensure the safety of the decontamination process. This review indicated the need for an integrated approach including decontamination studies using culture media and food matrices, proper identification and toxicity profiling of degraded products of aflatoxins, and interactions of microbes and the degradation products with food matrices for developing practical and effective microbial detoxification process.

Expression and application of aflatoxin degrading enzyme gene in Pichia pastoris

In this study, three aflatoxin degrading enzyme genes, tv-adtz, arm-adtz and cu-adtz, were heterologously expressed in Pichia pastoris. The protein expression of the enzyme solution was detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis, and the results showed that specific protein bands were detected and the target genes were successfully integrated into Pichia pastoris. The enzyme activities and detoxification efficiency of TV-ADTZ, Arm-ADTZ and Cu-ADTZ crude enzyme solutions were detected, and the highest enzyme activities were up to 3.57, 4.30, and 2.41 U mL-1 , and the highest degradation rates were up to 45.58%, 60.0% and 34.21%, respectively. Arm-ADTZ with the best degradation effect was selected and designed for detoxification application experiments to test its detoxification efficiency of AFB1 in aqueous phase and in the process of moldy ground corn and preparation of DDGS, respectively, and the degradation rates reached 78.94%, 56.48%, and 24.31% after 24 h of reaction, respectively. Thus, it can be seen that the aflatoxin-degrading enzyme gene was successfully integrated into Pichia pastoris and secreted for expression, and the expressed product could effectively degrade AFB1 .

Improvement of aflatoxin B1 degradation ability by Bacillus licheniformis CotA-laccase Q441A mutant

Aflatoxin B1 (AFB1) contamination seriously threatens nutritional safety and common health. Bacterial CotA-laccases have great potential to degrade AFB1 without redox mediators. However, CotA-laccases are limited because of the low catalytic activity as the spore-bound nature. The AFB1 degradation ability of CotA-laccase from Bacillus licheniformis ANSB821 has been reported by a previous study in our laboratory. In this study, a Q441A mutant was constructed to enhance the activity of CotA-laccase to degrade AFB1. After the site-directed mutation, the mutant Q441A showed a 1.73-fold higher catalytic efficiency (kcat/Km) towards AFB1 than the wild-type CotA-laccase did. The degradation rate of AFB1 by Q441A mutant was higher than that by wild-type CotA-laccase in the pH range from 5.0 to 9.0. In addition, the thermostability was improved after mutation. Based on the structure analysis of CotA-laccase, the higher catalytic efficiency of Q441A for AFB1 may be due to the smaller steric hindrance of Ala441 than Gln441. This is the first research to enhance the degradation efficiency of AFB1 by CotA-laccase with site-directed mutagenesis. In summary, the mutant Q441A will be a suitable candidate for highly effective detoxification of AFB1 in the future.

AFB1 Microbial Degradation by Bacillus subtilis WJ6 and Its Degradation Mechanism Exploration Based on the Comparative Transcriptomics Approach

Aflatoxin pollution poses great harm to human and animal health and causes huge economic losses. The biological detoxification method that utilizes microorganisms and their secreted enzymes to degrade aflatoxin has the advantages of strong specificity, high efficiency, and no pollution inflicted onto the environment. In this study, Bacillus subtilis WJ6 with a high efficiency in aflatoxin B₁ degradation was screened and identified through molecular identification, physiological, and biochemical methods. The fermentation broth, cell-free supernatant, and cell suspension degraded 81.57%, 73.27%, and 8.39% of AFB₁, respectively. The comparative transcriptomics analysis indicated that AFB₁ led to 60 up-regulated genes and 31 down-regulated genes in B. subtilis WJ6. A gene ontology (GO) analysis showed that the function classifications of cell aggregation, the organizational aspect, and the structural molecule activity were all of large proportions among the up-regulated genes. The down-regulated gene expression was mainly related to the multi-organism process function under the fermentation condition. Therefore, B. subtilis WJ6 degraded AFB₁ through secreted extracellular enzymes with the up-regulated genes of structural molecule activity and down-regulated genes of multi-organism process function.

Molecular Docking and Site-Directed Mutagenesis of GH49 Family Dextranase for the Preparation of High-Degree Polymerization Isomaltooligosaccharide

The high-degree polymerization of isomaltooligosaccharide (IMO) not only effectively promotes the growth and reproduction of Bifidobacterium in the human body but also renders it resistant to rapid degradation by gastric acid and can stimulate insulin secretion. In this study, we chose the engineered strain expressed dextranase (PsDex1711) as the research model and used the AutoDock vina molecular docking technique to dock IMO4, IMO5, and IMO6 with it to obtain mutation sites, and then studied the potential effect of key amino acids in this enzyme on its hydrolysate composition and enzymatic properties by site-directed mutagenesis method. It was found that the yield of IMO4 increased significantly to 62.32% by the mutant enzyme H373A. Saturation mutation depicted that the yield of IMO4 increased to 69.81% by the mutant enzyme H373R, and its neighboring site S374R IMO4 yield was augmented to 64.31%. Analysis of the enzymatic properties of the mutant enzyme revealed that the optimum temperature of H373R decreased from 30 °C to 20 °C, and more than 70% of the enzyme activity was maintained under alkaline conditions. The double-site saturation mutation results showed that the mutant enzyme H373R/N445Y IMO4 yield increased to 68.57%. The results suggest that the 373 sites with basic non-polar amino acids, such as arginine and histidine, affect the catalytic properties of the enzyme. The findings provide an important theoretical basis for the future marketable production of IMO4 and analysis of the structure of dextranase.

Microbial Enzymes Involved in the Biotransformation of Major Mycotoxins

Mycotoxins, the most researched biological toxins, can contaminate food and feed, resulting in severe health implications for humans and animals. Physical, chemical, and biological techniques are used to mitigate mycotoxin contamination. The biotransformation method using whole microbial cells or isolated enzymes is the best choice to mitigate mycotoxins. Using specific enzymes may avoid the disadvantages of utilizing a full microbe, such as accidental harm to the product's organoleptic characteristics and hazardous safety features. Moreover, the degradation rates of the isolated enzymes are higher than those of the whole-cell reactions, and they are substrate-specific. Their specificity is comprehensive and is shown at the positional and/or chiral center in many circumstances. Currently, only a few enzymes of microbial origin are commercially available. Therefore, there is a need to identify more novel enzymes of microbial origin that can mitigate mycotoxins. In this review, we conducted an in-depth summary of the microbial enzymes involved in the biotransformation of mycotoxins.

Characterization of a Trametes versicolor aflatoxin B1-degrading enzyme (TV-AFB1D) and its application in the AFB1 degradation of contaminated rice in situ

Aflatoxin B1 (AFB1) contaminates rice during harvest or storage and causes a considerable risk to human and animal health. In this study, Trametes versicolor AFB1-degrading enzyme (TV-AFB1D) gene recombinantly expressed in engineered E. coli BL21 (DE3) and Saccharomyces cerevisiae. The TV-AFB1D enzymatic characteristics and AFB1 degradation efficiency in contaminated rice were investigated. Results showed that the size of recombinant TV-AFB1D expressing in E. coli BL21 (DE3) and S. cerevisiae was appropriately 77 KDa. The kinetic equation of TV-AFB1D was y = 0.01671x + 1.80756 (R 2 = 0.994, Km  = 9.24 mM, and Vmax  = 553.23 mM/min). The Kcat and Kcat/Km values of TV-AFB1D were 0.07392 (s-1) and 8 M-1 s-1, respectively. The AFB1 concentration of contaminated rice decreased from 100 μg/ml to 32.6 μg/ml after treatment at 32°C for 5 h under the catabolism of TV-AFB1D. S. cerevisiae engineered strains carrying aldehyde oxidase 1 (AOX1) and Cauliflower mosaic virus 35 S (CaMV 35 S) promoters caused the residual AFB1 contents, respectively, decreased to 3.4 and 2.9 μg/g from the initial AFB1 content of 7.4 μg/g after 24 h of fermentation using AFB1-contaminated rice as substrate. The AFB1 degradation rates of S. cerevisiae engineered strains carrying AOX1 and CaMV promoters were 54 and 61%, respectively. Engineered S. cerevisiae strains integrated with TV-AFB1D expression cassettes were developed to simultaneously degrade AFB1 and produce ethanol using AFB1-contaminated rice as substrate. Thus, TV-AFB1D has significant application potential in the AFB1 decomposition from contaminated agricultural products.

Recent technological advances in mechanism, toxicity, and food perspectives of enzyme-mediated aflatoxin degradation

Aflatoxins are carcinogenic secondary metabolites produced by Aspergillus section Flavi that contaminates a wide variety of food and feed products and is responsible for serious health and economic consequences. Fermented foods are prepared with a wide variety of substrates over a long fermentation time and are thus vulnerable to contamination by aflatoxin-producing fungi, leading to the production of aflatoxin B1. The mitigation and control of aflatoxin is currently a prime focus for developing safe aflatoxin-free food. This review summarizes the role of major aflatoxin-degrading enzymes such as laccase, peroxidase, and lactonase, and microorganisms in the context of their application in food. A putative mechanism of enzyme-mediated aflatoxin degradation and toxicity evaluation of the degraded products are also extensively discussed to evaluate the safety of degradation processes for food applications. The review also describes aflatoxin-degrading microorganisms isolated from fermented products and investigates their applicability in food as aflatoxin preventing agents. Furthermore, a summary of recent technological advancements in protein engineering, nanozymes, in silico and statistical optimization approaches are explored to improve the industrial applicability of aflatoxin-degrading enzymes.