Structure-based rational design of a short-chain dehydrogenase/reductase for improving activity toward mycotoxin patulin

Identification and characterization of aldo-keto reductase responsible for patulin degradation in Saccharomyces cerevisiae

Patulin (PAT) is a hazardous mycotoxin that contaminates fruits and their products, causing significant economic losses. An aldo-keto reductase from Saccharomyces cerevisiae (ScAKR) was expressed in Escherichia coli in this study. The purified ScAKR converted PAT to E-ascladiol with NADPH as a cofactor. The ScAKR exhibited a strong degradation activity on PAT and the optimal degradation conditions were pH 7 and 37 °C. Molecular docking and site-specific mutagenesis indicated that the amino acids in ScAKR interacting with PAT aldehyde affected the degradation effect, and the mutation of Trp298 showed the most significant effect on the degradation rate. Furthermore, ScAKR also showed a strong degradation effect on 3-keto-deoxynivalenol, a metabolite of another mycotoxin, deoxynivalenol (DON). The findings offer new insights on the detoxification mechanism of PAT by S. cerevisiae and for the development and application of bioenzymes with broad-spectrum mycotoxin degradation properties.

Structural and catalytic insights into MhpB: A dioxygenase enzyme for degrading catecholic pollutants

The increasing environmental pollution from persistent aromatic compounds requires effective biodegradation strategies. In this study, we focused on MhpB, an extradiol dioxygenase (EDO) from Escherichia coli. It is known for its role in the degradation of catechols, key intermediates in the degradation of aromatic compounds. We report the high-resolution structure of MhpB determined by cryo-electron microscopy, revealing a decameric conformation with the catalytic chamber at the side. The structure-based analysis allowed us to investigate the substrate-enzyme interaction and the substrate selectivity, which are crucial for its catalytic function. Site-directed mutagenesis was used to modulate the in vitro and in vivo substrate preference of MhpB, enhancing its potential for industrial applications in pollutant degradation. The study provides insight into the mechanism of the enzyme and paves the way for the development of engineered EDOs for environmental remediation of aromatic pollutants.

Identification and Application of a Novel Patulin Degrading Enzyme From Meyerozyma guilliermondii

Patulin (PAT), a highly toxic mycotoxin, poses significant health risks due to its contamination of fruits and their derived products. Recent biological strategies for eliminating PAT mainly focus on elucidating the molecular detoxification processes of antagonistic microorganisms using omics technologies. However, there is still a scarcity of research on the rapid screening and catalytic mechanisms of bio-enzymes. In this study, a short-chain dehydrogenase/reductase (MgSDR1) capable of degrading PAT is rapidly identified from Meyerozyma guilliermondii by integrating transcriptomics with molecular docking. MgSDR1 completely degrades PAT into E-ascladiol within 2 h within the presence of reduced nicotinamide adenine dinucleotide phosphate (NADPH). Biodegradation efficiency is influenced by temperature, pH, enzyme/substrate concentrations, metal ions, and organic reagents. Notably, MgSDR1 shows efficient PAT degradation ability in fresh pear juice while maintaining key quality parameters, such as color parameters, pH, polyphenol oxidase activity, the contents of vitamin C, total phenols, titratable acidity, and soluble solids. The degradation process enhances the antioxidant capacity and enriches the aromatic compounds of the juice. Furthermore, site-directed mutagenesis reveals the essential role of the catalytic triad (Ser174-Tyr188-Lys192) in MgSDR1 activity. This study provides an efficient methodology for screening PAT-degrading enzymes and lays a theoretical foundation for the removal of mycotoxins in the food industry.

Metarhizium acridum transcription factor MaFTF1 negatively regulates virulence of the entomopathogenic fungus by controlling cuticle penetration of locusts

BACKGROUND

The entomopathogenic fungus (EPF) Metarhizium acridum, a typical filamentous fungus, has been utilized for the biological control of migratory locusts (Locusta migratoria manilensis). Fungal-specific transcription factors (TFs) play a crucial role in governing various cellular processes in fungi, although TFs with only the Fungal_trans domain remain poorly understood.

RESULTS

In this study, we identified a unique fungal-specific TF in M. acridum, named MaFTF1, which contains only a Fungal_trans domain and functions as a negative regulator of M. acridum virulence by influencing cuticle penetration. The virulence of the MaFTF1 knockout strain (ΔMaFTF1) against L. migratoria was increased, with a median lethal time (LT50) ~0.91 days shorter than that of the wild-type (WT) strain when inoculated topically, mimicking natural infection conditions. Correspondingly, ΔMaFTF1 penetrated the cuticle earlier than did the WT strain. Our investigation revealed that the development of appressoria was accelerated in ΔMaFTF1 compared with the WT strain. Furthermore, the appressoria of the ΔMaFTF1 displayed higher turgor pressure and an upregulated expression of fungal hydrolases active toward the insect cuticle. RNA sequencing analysis indicated that the differences in appressorium behavior between the strains were due to MaFTF1 regulating a complex metabolism pathway.

CONCLUSION

This study revealed that MaFTF1 acts as a negative regulator of virulence, impacting the process of cuticle penetration by slowing the formation of appressoria, decreasing their turgor pressure, and reducing the expression of hydrolases in appressoria, revealing an unexpected strategy in the EPFs. © 2024 Society of Chemical Industry.

Patulin Detoxification by Evolutionarily Divergent Reductases of Gluconobacter oxydans ATCC 621

The mycotoxin patulin in processed apple juice poses a significant threat to food safety, driving the need for effective detoxification strategies. Gluconobacter oxydans ATCC 621 can detoxify patulin to ascladiol using either the short-chain dehydrogenases/reductases (SDRs)─GOX0525, GOX1899, and GOX0716─or the aldo-keto reductase (AKR) GOX1462. While GOX0525 and GOX1899 have been previously characterized, this study focuses on GOX0716 and GOX1462, evaluating their optimal pH, thermostability, thermoactivity, and substrate specificity, thereby completing the characterization of all four reductases. GOX0716 and GOX1462 exhibit pH optima of 6 and 7, respectively, and are functional across a broad temperature range of 25-55 °C. GOX0716 was determined to be more thermostable than GOX1462, with a half-life of 4.95 h at 55 °C. Phylogenetic analysis revealed that these SDRs belong to distinct evolutionary families with broad substrate specificity. GOX0716 is a member of the SDR79 family, which shares a common ancestry with the SDR111 family of fungal anthrol reductases. Conversely, GOX1462 is a member of the AKR18 family, which is involved in detoxification of the mycotoxin, deoxynivalenol (DON). Molecular docking analysis of Alphafold models highlights distinct variations in the active site architectures of these SDRs and AKRs, offering insights into their differing catalytic efficiencies toward patulin.

Patulin-degrading enzymes sources, structures, and mechanisms: A review

Patulin (PAT), a fungal secondary metabolite with multiple toxicities, is an unavoidable contaminant in fruit and vegetable processing, posing potential health risks to consumers and causing significant economic losses to the global food industry. Traditional control strategies, such as physical and chemical methods, face several challenges, including low efficiency, high costs, and unverified safety. In contrast, microbial degradation of patulin is considered a more efficient and environmentally friendly approach, which has become a popular research focus. However, there is still insufficient research on the key degradation enzymes involved in microorganisms. Therefore, this review comprehensively summarizes recent research progress on the biological degradation of patulin, with a focus on microbial species capable of degrading patulin, the degradation enzymes they express, potential degradation mechanisms, and the toxicity of degradation products, while providing prospects for future research. It offers valuable insights for controlling patulin in food and stimulates further investigation. Ultimately, this review aims to promote the development of efficient and eco-friendly methods to mitigate patulin contamination in fruits and vegetables.

Identification and Application of Novel Patulin-Degrading Enzymes from Bacillus subtilis 168

Patulin (PAT), a toxic secondary metabolite produced mainly by Penicillium species that frequently contaminates fruit and fruit-derived products, poses serious health risks to humans and animals. In the present study, three short-chain dehydrogenases/reductases (SDRs) with PAT-degrading ability, designated BsSDR1, BsSDR2, and BsSDR3, were identified from the genome of Bacillus subtilis 168. BsSDR1 and BsSDR2 showed powerful PAT elimination abilities, which can completely convert PAT to nontoxic E-ascladiol. Moreover, BsSDR1, BsSDR2, and BsSDR3 shared the highest sequence identity of 36.03% with the reported PAT-degrading enzymes, indicating that they are novel PAT-degrading enzymes. BsSDR1, BsSDR2, and BsSDR3 exhibited the highest activity against PAT at 40, 40, and 35 °C, respectively. Additionally, BsSDR1, BsSDR2, and BsSDR3 displayed remarkable thermostability, retaining 32.50, 24.63, and 46.74% residual activity, respectively, after incubation at 50 °C for 1 h. Three-dimensional (3D) simulation and site-directed mutagenesis indicated that the catalytic triad formed by the residues (Ser, Tyr, and Lys) was the key for SDR activity, and this conserved catalytic mechanism was followed in the catalytic process of novel PAT-degrading enzymes BsSDR1, BsSDR2, and BsSDR3. More importantly, BsSDR1, BsSDR2, and BsSDR3 can degrade PAT in apple juice at rates of 86.90, 90.17, and 61.57%, respectively. The identification of BsSDR1, BsSDR2, and BsSDR3 enriched the PAT-degrading enzyme libraries, providing promising candidates for PAT decontamination in the food industry.

Current insights into yeast application for reduction of patulin contamination in foods: A comprehensive review

Patulin, a fungal secondary metabolite with multiple toxicities, is widely existed in a variety of fruits and their products. This not only causes significant economic losses to the agricultural and food industries but also poses a serious threat to human health. Conventional techniques mainly involved physical and chemical methods present several challenges include incomplete patulin degradation, high technical cost, and fruit quality decline. In comparison, removal of mycotoxin through biodegradation is regarded as a greener and safer strategy which has become popular research. Among them, yeast has a unique advantage in detoxification effect and application, which has attracted our attention. Therefore, this review provides a comprehensive account of the yeast species that can degrade patulin, degradation mechanism, current application status, and future challenges. Yeasts can efficiently convert patulin into nontoxic or low-toxic substances through biodegradation. Alternatively, it can use physical adsorption, which has the advantages of safety, high efficiency, and environmental friendliness. Nevertheless, due to the inherent complexity of the production environment, the sole utilization of yeast as a control agent remains inherently unstable and challenging to implement on a large scale in a practical manner. Integration control, enhancement of yeast resilience, improvement of yeast cell wall adsorption capacity, and research on additional patulin-degrading enzymes will facilitate the practical application of this approach. Furthermore, we analyzed the feasibility of the yeast commercial application in patulin reduction and provided suggestions on how to enhance its commercial value, which is of great significance for the control of mycotoxins in food products.

Functional characterization and structural basis of an efficient ochratoxin A-degrading amidohydrolase

Ochratoxin A (OTA) contamination in various agro-products poses a serious threat to the global food safety and human health, leading to enormous economic losses. Enzyme-mediated OTA degradation is an appealing strategy, and the search for more efficient enzymes is a prerequisite for achieving this goal. Here, a novel amidohydrolase, termed PwADH, was demonstrated to exhibit 7.3-fold higher activity than that of the most efficient OTA-degrading ADH3 previously reported. Cryo-electron microscopy structure analysis indicated that additional hydrogen-bond interactions among OTA and the adjacent residue H163, the more compact substrate-binding pocket, and the wider entry to the substrate-access cavity might account for the more efficient OTA-degrading activity of PwADH compared with that of ADH3. We conducted a structure-guided rational design of PwADH and obtained an upgraded variant, G88D, whose OTA-degrading activity was elevated by 1.2-fold. In addition, PwADH and the upgraded G88D were successfully expressed in the industrial yeast Pichia pastoris, and their catalytic activities were compared to those of their counterparts produced in E. coli, revealing the feasibility of producing PwADH and its variants in industrial yeast strains. These results illustrate the structural basis of a novel, efficient OTA-degrading amidohydrolase and will be beneficial for the development of high-efficiency OTA-degrading approaches.

Identification and application of a novel patulin degrading enzyme from Cyberlindnera fabianii

Patulin (PAT) is a mycotoxin commonly found in fruits and vegetables, prompting the need for effective removal and detoxification methods, which have garnered significant research attention in recent years. Among these methods, the utilization of microbial-derived enzymes stands out due to their mild operating conditions, specificity in targeted functional groups, and the production of non-toxic by-products, making it a preferred degradation approach. In this study, a novel PAT-degrading enzyme derived from Cyberlindnera fabianii (Cyfa-SDR) was identified, demonstrating its highest catalytic activity at pH 7.0 and 80 °C against PAT. This temperature tolerance level represents the highest reported for PAT-degrading enzymes to date. The enzyme was further characterized as a short-chain dehydrogenase through analysis of its amino acid composition, conserved GXXXGXG motif, and dependency on NADPH. Moreover, the study evaluated the efficiency of PAT degradation by Cyfa-SDR at varying substrate and enzyme concentrations, surpassing the performance of other PAT-degrading enzymes, thus highlighting its substantial potential for the biological control of PAT. In conclusion, the enzymatic treatment using the PAT-degrading enzyme Cyfa-SDR presents a viable and promising solution for enhancing the quality and safety of fruit juice.

Structural and functional insights into the self-sufficient flavin-dependent halogenase

Flavin-dependent halogenases (FDHs) have tremendous applications in synthetic chemistry. A single-component FDH, AetF, exhibits both halogenase and reductase activities in a continuous polypeptide chain. AetF exhibits broad substrate promiscuity and catalyzes the two-step bromination of l-tryptophan (l-Trp) to produce 5-bromotryptophan (5-Br-Trp) and 5,7-dibromo-l-tryptophan (5,7-di-Br-Trp). To elucidate the mechanism of action of AetF, we solved its crystal structure in complex with FAD, FAD/NADP+, FAD/l-Trp, and FAD/5-Br-Trp at resolutions of 1.92-2.23 Å. The obtained crystal structures depict the unprecedented topology of single-component FDH. Structural analysis revealed that the substrate flexibility and dibromination capability of AetF could be attributed to its spacious substrate-binding pocket. In addition, highly-regulated interaction networks between the substrate-recognizing residues and 5-Br-Trp are crucial for the dibromination activity of AetF. Several Ala variants underwent monobromination with >98 % C5-regioselectivity toward l-Trp. These results reveal the catalytic mechanism of single-component FDH for the first time and contribute to efficient FDH protein engineering for biocatalytic halogenation.

Self-cascade deoxynivalenol detoxification by an artificial enzyme with bifunctions of dehydrogenase and aldo/keto reductase from genome mining

Due to the severe health risks for human and animal caused by the intake of toxic deoxynivalenol (DON) derived from Fusarium species, elimination DON in food and feed has been initiated as a critical issue. Enzymatic cascade catalysis by dehydrogenase and aldo-keto reductase represents a fascinating strategy for DON detoxification. Here, one quinone-dpendent alcohol dehydrogenase DADH oxidized DON into less-toxic 3-keto-DON and NADPH-dependent aldo-keto reductase AKR13B3 reduced 3-keto-DON into relatively non-toxic 3-epi-DON were identified from Devosia strain A6-243, indicating that degradation of DON on C3 are two-step sequential cascade processes. To establish the bifunctions, fusion enzyme linking DADH and AKR13B3 was successfully assembled to promote one-step DON degradations with accelerated specific activity and efficiency, resulting 93.29 % of DON removal rate in wheat sample. Three-dimensional simulation analysis revealed that the bifunctional enzyme forms an artificial intramolecular channel to minimize the distance of intermediate from DADH to AKR13B3 for two-step enzymatic reactions, and thereby accelerates this enzymatic process. As the first report of directing single step DON detoxification by an interesting bifunctional artificial enzyme, this work revealed a facile and eco-friendly approach to detoxify DON with application potential and gave valuable insights into execute other mycotoxin detoxification for ensuring food safety.