A new lipoxygenase from the agaric fungus Agrocybe aegerita: Biochemical characterization and kinetic properties

Purification and Biochemical Characterization of Novel Galectin from the Black Poplar Medicinal Mushroom Cyclocybe cylindracea (Agaricomycetes) Strain MEST42 from Algeria

In the present study, a new galectin designated Cyclocybe cylindracea lectin (CCL) was extracted from the fruiting bodies of the wild black popular mushroom C. cylindracea grown in Algeria. The protein was isolated using sepharose 4B as affinity chromatography matrix, and galactose as elutant. The purified galectin was composed of two subunits of 17.873 kDa each, with a total molecular mass of 35.6 kDa. Its agglutinant activity was impeded by galactose and its derivatives, as well as melibiose. Lactose showed the highest affinity, with a minimal inhibitory concentration of 0.0781 mM. CCL was sensitive to extreme pH conditions, and its binding function decreased when incubated with 10 mM EDTA, and it could be restored by metallic cations such as Ca2+, Mg2+, and Zn2+. CCL agglutinated human red blood cells, without any discernible specificity. Circular dichroism spectra demonstrated that its secondary structure contained β-sheet as dominant fold. In addition, bioinformatics investigation on their peptide fingerprint obtained after MALDI-TOF/TOF ionization using mascot software confirmed that CCL was not like any previous purified lectin from mushroom: instead, it possessed an amino acid composition with high similarity to that of the putative urea carboxylase of Emericella nidulans (strain FGSC A4/ATCC 38163/CBS 112.46/NRRL 194/M139) with 44% of similarity score.

Improved catalytic performance and molecular insight for lipoxygenase from Enterovibrio norvegicus via directed evolution

Lipoxygenase (LOX) holds significant promise for food and pharmaceutical industries. However, albeit its application has been hampered by low catalytic activity and suboptimal thermostability. To address the drawbacks, a directed evolution strategy was explored to enhance the catalytic activity and thermostability of LOX from Enterovibrio norvegicus (EnLOX) for the first time. After two rounds of error-prone polymerase chain reaction (error-prone PCR) and one generations of sequential DNA shuffling, all of four different mutants showed a significant increase in the specific activity of EnLOX, ranging from 132.07 ± 9.34 to 330.17 ± 18.54 U/mg. Among these mutants, D95E/T99A/A121H/S142N/N444W/S613G (EAHNWG) exhibited the highest specific activity, which was 8.25-fold higher than the wild-type enzyme (WT). Meanwhile, the catalytic efficiency (K cat /K m) of EAHNWG was also improved, which was 13.61 ± 1.67 s-1 μM-1, in comparison to that of WT (4.83 ± 0.38 s-1 μM-1). In addition, mutant EAHNWG had a satisfied thermostability with the t 1/2,50 °C value of 6.44 ± 0.24 h, which was 0.4 h longer than that of the WT. Furthermore, the molecular dynamics simulation and structural analysis demonstrated that the reduction of hydrogen bonds number, the enhancement of hydrophobic interactions in the catalytic pocket, and the improvement of flexibility of the lid domain facilitated structural stability and the strength of substrate binding capacity for improved thermal stability and catalytic efficiency of mutant LOX after directed evolution. Overall, these results could provide the guidance for further enzymatic modification of LOX with high catalytic performance for industrial application.

Computational Insights and In Silico Characterization of a Novel Mini-Lipoxygenase from Nostoc Sphaeroides and Its Application in the Quality Improvement of Steamed Bread

Lipoxygenase (EC1.13.11.12, LOX) has been potentially used in the food industry for food quality improvement. However, the low activity, poor thermal stability, narrow range of pH stability, as well as undesirable isoenzymes and off-flavors, have hampered the application of current commercial LOX. In this study, a putative mini-lipoxygenase gene from cyanobacteria, Nostoc sphaeroides (NsLOX), was cloned and expressed in E. coli BL21. NsLOX displayed only 26.62% structural identity with the reported LOX from Cyanothece sp., indicating it as a novel LOX. The purified NsLOX showed the maximum activity at pH 8.0 and 15 °C, with superior stability at a pH range from 6.0 to 13.0, retaining about 40% activity at 40 °C for 90 min. Notably, NsLOX exhibited the highest specific activity of 78,080 U/mg towards linoleic acid (LA), and the kinetic parameters-K_m, k_cat, and k_cat/K_m-attain values of 19.46 μM, 9199.75 s^-1, and 473.85 μM^-1 s^-1, respectively. Moreover, the activity of NsLOX was obviously activated by Ca²⁺, but it was completely inhibited by Zn²⁺ and Cu²⁺. Finally, NsLOX was supplied in steamed bread and contributed even better improved bread quality than the commercial LOX. These results suggest NsLOX as a promising substitute of current commercial LOX for application in the food industry.

Characterization and Preliminary Application of a Novel Lipoxygenase from Enterovibrio norvegicus

Lipoxygenases have proven to be a potential biocatalyst for various industrial applications. However, low catalytic activity, low thermostability, and narrow range of pH stability largely limit its application. Here, a lipoxygenase (LOX) gene from Enterovibrio norvegicus DSM 15893 (EnLOX) was cloned and expressed in Escherichia coli BL21 (DE3). EnLOX showed the catalytic activity of 40.34 U mg⁻¹ at 50 °C, pH 8.0. Notably, the enzyme showed superior thermostability, and wide pH range stability. EnLOX remained above 50% of its initial activity after heat treatment below 50 °C for 6 h, and its melting point temperature reached 78.7 °C. More than 70% of its activity was maintained after incubation at pH 5.0–9.5 and 4 °C for 10 h. In addition, EnLOX exhibited high substrate specificity towards linoleic acid, and its kinetic parameters of V_max, K_m, and K_cat values were 12.42 mmol min⁻¹ mg⁻¹, 3.49 μmol L⁻¹, and 16.86 s⁻¹, respectively. LC-MS/MS analysis indicated that EnLOX can be classified as 13-LOX, due to its ability to catalyze C₁₈ polyunsaturated fatty acid to form 13-hydroxy fatty acid. Additionally, EnLOX could improve the farinograph characteristics and rheological properties of wheat dough. These results reveal the potential applications of EnLOX in the food industry.

Iron and manganese lipoxygenases of plant pathogenic fungi and their role in biosynthesis of jasmonates

Lipoxygenases (LOX) contain catalytic iron (FeLOX), but fungi also produce LOX with catalytic manganese (MnLOX). In this review, the 3D structures and properties of fungal LOX are compared and contrasted along with their associations with pathogenicity. The 3D structures and properties of two MnLOX (Magnaporthe oryzae, Geaumannomyces graminis) and the catalysis of five additional MnLOX have provided information on the metal center, substrate binding, oxygenation, tentative O₂ channels, and biosynthesis of exclusive hydroperoxides. In addition, the genomes of other plant pathogens also code for putative MnLOX. Crystals of the 13S-FeLOX of Fusarium graminearum revealed an unusual altered geometry of the Fe ligands between mono- and dimeric structures, influenced by a wrapping sequence extension near the C-terminal of the dimers. In plants, the enzymes involved in jasmonate synthesis are well documented whereas the fungal pathway is yet to be fully elucidated. Conversion of deuterium-labeled 18:3n-3, 18:2n-6, and their 13S-hydroperoxides to jasmonates established 13S-FeLOX of F. oxysporum in the biosynthesis, while subsequent enzymes lacked sequence homologues in plants. The Rice-blast (M. oryzae) and the Take-all (G. graminis) fungi secrete MnLOX to support infection, invasive hyphal growth, and cell membrane oxidation, contributing to their devastating impact on world production of rice and wheat.

Biotransformation of [U-13C]linoleic acid suggests two independent ketonic- and aldehydic cycles within C8-oxylipin biosynthesis in Cyclocybe aegerita (V. Brig.) Vizzini

Although the typical aroma contributing compounds in fungi of the phylum Basidiomycota are known for decades, their biosynthetic pathways are still unclear. Amongst these volatiles, C8-compounds are probably the most important ones as they function, in addition to their specific perception of fungal odour, as oxylipins. Previous studies focused on C8-oxylipin production either in fruiting bodies or mycelia. However, comparisons of the C8-oxylipin biosynthesis at different developmental stages are scarce, and the biosynthesis in basidiospores was completely neglected. In this study, we addressed this gap and were able to show that the biosynthesis of C8-oxylipins differs strongly between different developmental stages. The comparison of mycelium, primordia, young fruiting bodies, mature fruiting bodies, post sporulation fruiting bodies and basidiospores revealed that the occurance of the two main C8-oxylipins octan-3-one and oct-1-en-3-ol distinguished in different stages. Whereas oct-1-en-3-ol levels peaked in the mycelium and decreased with ongoing maturation, octan-3-one levels increased during maturation. Furthermore, oct-2-en-1-ol, octan-1-ol, oct-2-enal, octan-3-ol, oct-1-en-3-one and octanal contributed to the C8-oxylipins but with drastically lower levels. Biotransformations with [U-13C]linoleic acid revealed that early developmental stages produced various [U-13C]oxylipins, whereas maturated developmental stages like post sporulation fruiting bodies and basidiospores produced predominantly [U-13C]octan-3-one. Based on the distribution of certain C8-oxylipins and biotransformations with putative precursors at different developmental stages, two distinct biosynthetic cycles were deduced with oct-2-enal (aldehydic-cycle) and oct-1-en-3-one (ketonic-cycle) as precursors.

Transcriptome of different fruiting stages in the cultivated mushroom Cyclocybe aegerita suggests a complex regulation of fruiting and reveals enzymes putatively involved in fungal oxylipin biosynthesis

BACKGROUND

Cyclocybe aegerita (syn. Agrocybe aegerita) is a commercially cultivated mushroom. Its archetypal agaric morphology and its ability to undergo its whole life cycle under laboratory conditions makes this fungus a well-suited model for studying fruiting body (basidiome, basidiocarp) development. To elucidate the so far barely understood biosynthesis of fungal volatiles, alterations in the transcriptome during different developmental stages of C. aegerita were analyzed and combined with changes in the volatile profile during its different fruiting stages.

RESULTS

A transcriptomic study at seven points in time during fruiting body development of C. aegerita with seven mycelial and five fruiting body stages was conducted. Differential gene expression was observed for genes involved in fungal fruiting body formation showing interesting transcriptional patterns and correlations of these fruiting-related genes with the developmental stages. Combining transcriptome and volatilome data, enzymes putatively involved in the biosynthesis of C8 oxylipins in C. aegerita including lipoxygenases (LOXs), dioxygenases (DOXs), hydroperoxide lyases (HPLs), alcohol dehydrogenases (ADHs) and ene-reductases could be identified. Furthermore, we were able to localize the mycelium as the main source for sesquiterpenes predominant during sporulation in the headspace of C. aegerita cultures. In contrast, changes in the C8 profile detected in late stages of development are probably due to the activity of enzymes located in the fruiting bodies.

CONCLUSIONS

In this study, the combination of volatilome and transcriptome data of C. aegerita revealed interesting candidates both for functional genetics-based analysis of fruiting-related genes and for prospective enzyme characterization studies to further elucidate the so far barely understood biosynthesis of fungal C8 oxylipins.

Engineering a lipoxygenase from cyclocybe aegerita towards long chain polyunsaturated fatty acids

The basidiomycetous lipoxygenase Lox1 from Cyclocybe aegerita catalyzes the oxygenation of polyunsaturated fatty acids (PUFAs) with a high preference towards the C18-PUFA linoleic acid (C18:2 (ω-6)). In contrast, longer PUFAs, generally not present in the fungal cell such as eicosatrienoic acid (C20:3(ω-3)) and docosatrienoic acid (C22:3 (ω-3)), are converted with drastically lower activities. With site-directed mutagenesis, we were able to create two variants with enhanced activities towards longer chain PUFAs. The W330L variant showed a ~ 20 % increased specific activity towards C20:3(ω-3), while a ~ 2.5-fold increased activity against C22:3 (ω-3) was accomplished by the V581 variant.

Synthesis of two new lipid mediators from docosahexaenoic acid by combinatorial catalysis involving enzymatic and chemical reaction

Omega-3 polyunsaturated fatty acids (PUFAs) have been known to have beneficial effects in the prevention of various diseases. Recently, it was identified that the bioactivities of omega-3 are related to lipid mediators, called pro-resolving lipid mediators (SPMs), converted from PUFAs, so they have attracted much attention as potential pharmaceutical targets. Here, we aimed to build an efficient production system composed of enzymatic and chemical catalysis that converts docosahexaenoic acid (DHA) into lipid mediators. The cyanobacterial lipoxygenase, named Osc-LOX, was identified and characterized, and the binding poses of enzyme and substrates were predicted by ligand docking simulation. DHA was converted into three lipid mediators, a 17S-hydroxy-DHA, a 7S,17S-dihydroxy-DHA (RvD5), and a 7S,15R-dihydroxy-16S,17S-epoxy-DPA (new type), by an enzymatic reaction and deoxygenation. Also, two lipid mediators, 7S,15R,16S,17S-tetrahydroxy-DPA (new type) and 7S,16R,17S-trihydroxy-DHA (RvD2), were generated from 7S,15R-dihydroxy-16S,17S-epoxy-DPA by a chemical reaction. Our study suggests that discovering new enzymes that have not been functionally characterized would be a powerful strategy for producing various lipid mediators. Also, this combination catalysis approach including biological and chemical reactions could be an effective production system for the manufacturing lipid mediators.

Multilocus phylogeny- and fruiting feature-assisted delimitation of European Cyclocybe aegerita from a new Asian species complex and related species

Cyclocybe aegerita (synonym: Agrocybe aegerita) is a widely cultivated edible and reportedly almost cosmopolitan mushroom species that serves as a model fungus for basidiome formation and as producer of useful natural products and enzymes. Focusing on strains from different continents, here, we present a phylogenetic analysis of this species and some adjacent taxa that employs four phylogenetic markers. In addition, we tested the strains’ capability to fructify on agar media. Our analysis reveals that “C. aegerita sensu lato” splits up into the following two well-supported monophyletic geographic lineages: a European clade and an Asian clade. The European one is closely associated with the Chinese species Cyclocybe salicaceicola. In contrast, the Asian lineage, which we preliminarily designate as Cyclocybe chaxingu agg., may comprise several species (species complex) and clusters with the Pacific species Cyclocybe parasitica (New Zealand). In addition, fruiting properties differ across C. aegerita and its Asian and Pacific relatives; however, strains from the Asian clade and C. parasitica tend to form larger basidiomes with relatively big caps and long stipes and strains from the European clade exhibit a more variable fruiting productivity with the tendency to form more basidiomes, with smaller caps and shorter stipes. Moreover, some strains showed individual fruiting patterns, such as the preference to fruit where they were exposed to injuring stimuli. In conclusion, the delimitation of the newly delimited Asian species complex from our multilocus phylogeny of “C. aegerita sensu lato”, which is supported by phenotypic data, depicts an exemplary case of biogeographic diversity within a previously thought homogeneous species of near worldwide distribution.

The Lipoxygenase Lox1 Is Involved in Light- and Injury-Response, Conidiation, and Volatile Organic Compound Biosynthesis in the Mycoparasitic Fungus Trichoderma atroviride

The necrotrophic mycoparasite Trichoderma atroviride is a biological pest control agent frequently applied in agriculture for the protection of plants against fungal phytopathogens. One of the main secondary metabolites produced by this fungus is 6-pentyl-α-pyrone (6-PP). 6-PP is an organic compound with antifungal and plant growth-promoting activities, whose biosynthesis was previously proposed to involve a lipoxygenase (Lox). In this study, we investigated the role of the single lipoxygenase-encoding gene lox1 encoded in the T. atroviride genome by targeted gene deletion. We found that light inhibits 6-PP biosynthesis but lox1 is dispensable for 6-PP production as well as for the ability of T. atroviride to parasitize and antagonize host fungi. However, we found Lox1 to be involved in T. atroviride conidiation in darkness, in injury-response, in the production of several metabolites, including oxylipins and volatile organic compounds, as well as in the induction of systemic resistance against the plant-pathogenic fungus Botrytis cinerea in Arabidopsis thaliana plants. Our findings give novel insights into the roles of a fungal Ile-group lipoxygenase and expand the understanding of a light-dependent role of these enzymes.