Expression of 5,8-LDS of Aspergillus fumigatus and its dioxygenase domain. A comparison with 7,8-LDS, 10-dioxygenase, and cyclooxygenase

Review of key issues and potential strategies in bio-degradation of polyolefins

Polyolefins are the most widely used plastic product and a major contributor to white pollution. Currently, studies on polyolefin degradation systems are mainly focused on microorganisms and some redox enzymes, and there is a serious black-box phenomenon. The use of polyolefin-degrading enzymes is limited because of the small number of enzymes; in addition, the catalytic efficiency of these enzymes is poor and their catalytic mechanism is unclear, which leads to the incomplete degradation of polyolefins to produce microplastics. In this review, three questions are addressed: the generation and degradation of action targets that promote the degradation of polyolefins, the different modes by which enzymes bind substrates and their application scenarios, and possible multienzyme systems in a unified system. This review will be valuable for mining or modifying polyolefin degradation enzymes and constructing polyolefins degradation systems and may provide novel ideas and opportunities for polyolefin degradation.

Production of 8,11-dihydroxy fatty acids from oleic and palmitoleic acids by Escherichia coli cells expressing variant 6,8-linoleate diol synthases from Penicillium oxalicum

Recombinant Escherichia coli cells expressing 8,11-linoleate diol synthase (LDS) from Penicillium chrysogenum convert oleic and palmitoleic acids to 8-hydroperoxy-9(Z)-octadecenoic acid (HPOME) and 8-hydroperoxy-9(Z)-hexadecenoic acid (HPHME) only, respectively. However, recombinant E. coli cells expressing Q889A variant 6,8-LDS from Penicillium oxalicum as an 8,11-LDS converted oleic and palmitoleic acids to 8,11-dihydroxy-9(Z)-octadecenoic acid (DiHOME) and 8,11-dihydroxy-9(Z)-hexadecenoic acid (DiHHME), respectively, which were identified using LC-MS/MS analysis. To select suitable variants for producing these compounds, position 889 of 6,8-LDS from P. oxalicum was substituted with other amino acids, and recombinant E. coli cells expressing Q889L and Q889A variants were chosen as the best biocatalysts for producing 8,11-DiHOME and 8,11-DiHHME, respectively. The optimal conditions for producing 8,11-DiHOME or 8,11-DiHHME using cells expressing Q889L or Q889A variant 6,8-LDS were pH 6.5 and 30 °C with 5% (v/v) dimethyl sulfoxide (DMSO), 60 g L^-1 cells, and 10 g L^-1 oleic acid or 7.5 g L^-1 palmitoleic acid, respectively. Under these conditions, 10.7 g L^-1 8,11-DiHOME and 8.1 g L^-1 8,11-DiHHME were produced for 1.5 h with molar yields of 96.4 and 96.2% and productivities of 7.1 and 5.4 g L^-1  h^-1 , respectively. The molar yields and concentrations of 8,11-DiHOME and 8,11-DiHHME were highest among those of other reported DiHOMEs and DiHHMEs. To the best of our knowledge, this is the first quantitative production of 8,11-DiHOME and 8,11-DiHHME. This article is protected by copyright. All rights reserved.

Fatty acid dioxygenase-cytochrome P450 fusion enzymes of filamentous fungal pathogens

Oxylipins designate oxygenated unsaturated C₁₈ fatty acids. Many filamentous fungi pathogens contain dioxygenases (DOX) in oxylipin biosynthesis with homology to human cyclooxygenases. They contain a DOX domain, which is often fused to a functional cytochrome P450 at the C-terminal end. A Tyr radical in the DOX domain initiates dioxygenation of linoleic acid by hydrogen abstraction with formation of 8-, 9-, or 10-hydroperoxy metabolites. The P450 domains can catalyze heterolytic cleavage of 8- and 10-hydroperoxides with oxidation of the heme thiolate iron for hydroxylation at C-5, C-7, C-9, or C-11 and for epoxidation of the 12Z double bond; thus displaying linoleate diol synthase (LDS) and epoxy alcohol synthase (EAS) activities. LSD activities are present in the rice blast pathogen Magnaporthe oryzae, Botrytis cinerea causing grey mold and the black scurf pathogen Rhizoctonia solani. 10R-DOX-EAS has been found in M. oryzae and Fusarium oxysporum. The P450 domains may also catalyze homolytic cleavage of 8- and 9-hydroperoxy fatty acids and dehydration to produce epoxides with an adjacent double bond, i.e., allene oxides, thus displaying 8- and 9-DOX-allene oxide synthases (AOS). F. oxysporum, F. graminearum, and R. solani express 9S-DOX-AOS and Zymoseptoria tritici 8S-and 9R-DOX-AOS. Homologues are present in endemic human-pathogenic fungi with extensive studies in Aspergillus fumigatus, A. flavus (also a plant pathogen) as well as the genetic model A. nidulans. 8R-and 10R-DOX appear to bind fatty acids "headfirst" in the active site, whereas 9S-DOX binds them "tail first" in analogy with cyclooxygenases. The biological relevance of 8R-DOX-5,8-LDS (also designated PpoA) was first discovered in relation to sporulation of A. nidulans and recently for development and programmed hyphal branching of A. fumigatus. Gene deletion DOX-AOS homologues in F. verticillioides, A. flavus, and A. nidulans alters, inter alia, mycotoxin production, sporulation, and gene expression.

Potential hypoglycemic metabolites in dark tea fermented by Eurotium cristatum based on UPLC-QTOF-MS/MS combining global metabolomic and spectrum-effect relationship analyses

The preventive and therapeutic effects of dark tea fermented by Eurotium cristatum (DTE) in glucose metabolism have been demonstrated. However, few studies have investigated comprehensive changes in the chemical composition and activity in DTE before and after fermentation. In this study, the metabolic profiling of raw samples and fermented samples was determined by ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS/MS). Furthermore, a systematic analytical strategy combining global metabolomics and the spectrum-effect relationship based on α-glucosidase inhibition was employed for screening discriminant metabolites. As a result, 15 discriminant metabolites were identified in DTE samples. Among them, 10 metabolites (4 fatty acids, 1 dyphylline derivative, 3 lysophosphatidylcholines, and 2 triterpenes) increased in relative contents and the contents of the other 5 polyphenol metabolites decreased after fermentation. These metabolites were critical constituents possibly associated with DTE's hypoglycemic activity, which also might be suitable as quality evaluation indicators. This study provided a worthy insight into the exploration of representative active constituents or quality indicators of DTE.

WITHDRAWN: Fatty acid dioxygenase-cytochrome P450 fusion enzymes of the top 10 fungal pathogens in molecular plant pathology and human-pathogenic fungi

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Molecular characterization of Penicillium oxalicum 6R,8R-linoleate diol synthase with new regiospecificity

Diol synthase-derived metabolites are involved in the sexual and asexual life cycles of fungi. A putative diol synthase from Penicillium oxalicum was found to convert palmitoleic acid (16:1n-7), oleic acid (18:1n-9), linoleic acid (18:2n-6), and α-linolenic acid (18:3n-3) to 6S,8R-dihydroxy-9(Z)-hexadecenoic acid, 6R,8R-dihydroxy-9(Z)-octadecenoic acid, 6R,8R-dihydroxy-9,12(Z,Z)-octadecadienoic acid, and 6S,8R-dihydroxy-9,12,15(Z,Z,Z)-octadecatrienoic acid, respectively, which were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and nuclear magnetic resonance (NMR) spectroscopy analyses. The specific activity and catalytic efficiency of P. oxalicum 6,8-diol synthase were the highest for 18:2n-6, indicating that the enzyme is a 6R,8R-linoleate diol synthase (6R,8R-LDS) with new regiospecificity. This is the first report of a 6R,8R-LDS. LDS is a fusion protein consisting of a dioxygenase domain at the N-terminus and a cytochrome P450/hydroperoxide isomerase (P450/HPI) domain at the C-terminus. The putative active-site residues in the C-terminal domain of P. oxalicum 6R,8R-LDS were proposed based on a substrate-docking homology model. The results of the site-directed mutagenesis within C-terminal P450 domain suggested that Asn⁸⁸⁶, Arg⁷⁰⁷, and Arg⁹³⁴, are catalytic importance and belong to the catalytic groove. Phe⁷⁹⁴ and Gln⁸⁸⁹ were found to be involved in the regiospecific rearrangement of hydroperoxide, while the F794E and Q889A variants of P. oxalicum 6,8-LDS acted as 7,8- and 8,11-LDSs, respectively. All these mutations critically affected the HPI activity of P. oxalicum 6R,8R-LDS.

Biosynthesis of Oxylipins by Rhizoctonia solani with Allene Oxide and Oleate 8S,9S-Diol Synthase Activities

Oxylipin biosynthesis by fungi is catalyzed by both the lipoxygenase (LOX) family and the linoleate diol synthase (LDS) family of the peroxidase-cyclooxygenase superfamily. Rhizoctonia solani, a pathogenic fungus, infects staple crops such as potato and rice. The genome predicts three genes with 9-13 introns, which code for tentative dioxygenase (DOX)-cytochrome P450 fusion enzymes of the LDS family, and one gene, which might code for a 13-LOX. The objective was to determine whether mycelia or nitrogen powder of mycelia oxidized unsaturated C₁₈ fatty acids to LDS- or LOX-related metabolites. Mycelia converted 18:2n-6 to 8R-hydroxy-9Z,12Z-octadecadienoic acid and to an α-ketol, 9S-hydroxy-10-oxo-12Z-octadecenoic acid. In addition to these metabolites, nitrogen powder of mycelia oxidized 18:2n-6 to 9S-hydroperoxy-10E, 12Z-octadecadienoic, and 13S-hydroperoxy-9Z,11E-octadecadienoic acids; the latter was likely formed by the predicted 13-LOX. 18:1n-9 was transformed into 8S-hydroperoxy-9Z-octadecenoic and into 8S,9S-dihydroxy-10E-octadecenoic acids, indicating the expression of 8,9-diol synthase. The allene oxide, 9S(10)epoxy-10,12Z-octadecadienoic acid, is unstable and decomposes rapidly to the α-ketol above, indicating biosynthesis by 9S-DOX-allene oxide synthase. This allene oxide and α-ketol are also formed by potato stolons, which illustrates catalytic similarities between the plant host and fungal pathogen.

Product specificity of fungal 8R- and 9S-dioxygenases of the peroxidase-cyclooxygenase superfamily with amino acid derivatized polyenoic fatty acids

Pathogenic fungi express fatty acid dioxygenases (DOX) fused to cytochromes P450 with diol or allene oxide synthase activities. The orientation of the fatty acids in the active sites of DOX was investigated with amino acid conjugates of 18:3n-3 and 18:2n-6. 9S-DOX-allene oxide synthase (AOS) oxidized the Gly, Ile, and Trp derivatives at C-9, which suggests that these conjugates enter the substrate recognition site with the omega end in analogy with fatty acids bound to cyclooxygenases and coral 8R-lipoxygenase (8R-LOX). In contrast, 7,8-diol synthases (7,8-LDS), 5,8-LDS, and 8R-DOX-AOS oxidized the Gly conjugates in most case only to small amounts of metabolites, but with retention of hydrogen abstraction at C-8 and relatively minor hydrogen abstraction at C-11. The Ile and Trp conjugates were not oxidized at C-8, and often insignificantly at C-9/C-13. The 8-DOX domains of these enzymes likely position the carboxyl group of substrates at the end of the active site in analogy with plant α-DOX and 9-LOX. Tyr radicals of the 9S-DOX and 8R-DOX domains catalyze antarafacial hydrogen abstraction and oxygen insertion in 18:3n-3. This occurs by abstraction of the proR and proS hydrogens at C-11 and C-8, respectively, in agreement with different "head to tail" orientation in the active site.

Production of 7,8-Dihydroxy Unsaturated Fatty Acids from Plant Oils by Whole Recombinant Cells Expressing 7,8-Linoleate Diol Synthase from Glomerella cingulata

The reaction conditions for the production of 7S,8S-dihydroxy-9,12(Z,Z)-octadecadienoic acid from linoleic acid by recombinant Escherichia coli expressing 7,8-linoleate diol synthase from Glomerella cingulata were optimized using response surface methodology. The optimal reaction conditions were pH 7.0, 18.6 °C, 10.8% (v/v) dimethyl sulfoxide, 44.9 g/L cells, and 14.3 g/L linoleic acid, with agitation at 256 rpm. Under these conditions, recombinant cells produced 7,8-dihydroxy unsaturated fatty acids in the range of 7.0-9.8 g/L from 14.3 g/L linoleic acid, 14.3 g/L oleic acid, and plant oil hydrolysates such as waste oil and olive oil containing 14.3 g/L linoleic acid or oleic acid. To the best of the authors' knowledge, this is the first report on the biotechnological production of 7,8-dihydroxy unsaturated fatty acids.

A new class of fatty acid allene oxide formed by the DOX-P450 fusion proteins of human and plant pathogenic fungi, C. immitis and Z. tritici

Linoleate dioxygenase-cytochrome P450 (DOX-CYP) fusion enzymes are common in pathogenic fungi. The DOX domains form hydroperoxy metabolites of 18:2n-6, which can be transformed by the CYP domains to 1,2- or 1,4-diols, epoxy alcohols, or to allene oxides. We have characterized two novel allene oxide synthases (AOSs), namely, recombinant 8R-DOX-AOS of Coccidioides immitis (causing valley fever) and 8S-DOX-AOS of Zymoseptoria tritici (causing septoria tritici blotch of wheat). The 8R-DOX-AOS oxidized 18:2n-6 sequentially to 8R-hydroperoxy-9Z,12Z-octadecadienoic acid (8R-HPODE) and to an allene oxide, 8R(9)-epoxy-9,12Z-octadecadienoic acid, as judged from the accumulation of the α-ketol, 8S-hydroxy-9-oxo-12Z-octadecenoic acid. The 8S-DOX-AOS of Z. tritici transformed 18:2n-6 sequentially to 8S-HPODE and to an α-ketol, 8R-hydroxy-9-oxo-12Z-octadecenoic acid, likely formed by hydrolysis of 8S(9)-epoxy-9,12Z-octadecadienoic acid. The 8S-DOX-AOS oxidized [8R-(2)H]18:2n-6 to 8S-HPODE with retention of the (2)H-label, suggesting suprafacial hydrogen abstraction and oxygenation in contrast to 8R-DOX-AOS. Both enzymes oxidized 18:1n-9 and 18:3n-3 to α-ketols, but the catalysis of the 8R- and 8S-AOS domains differed. 8R-DOX-AOS transformed 9R-HPODE to epoxy alcohols, but 8S-DOX-AOS converted 9S-HPODE to an α-ketol (9-hydroxy-10-oxo-12Z-octadecenoic acid) and epoxy alcohols in a ratio of ∼1:2. Whereas all fatty acid allene oxides described so far have a conjugated diene impinging on the epoxide, the allene oxides formed by 8-DOX-AOS are unconjugated.

Characterization of a novel 8R,11S-linoleate diol synthase from Penicillium chrysogenum by identification of its enzymatic products

To identify novel fatty acid diol synthases, putative candidate sequences from Penicillium species were analyzed, and hydroxy fatty acid production by crude Penicillium enzyme extracts was assessed. Penicillium chrysogenum was found to produce an unknown dihydroxy fatty acid, a candidate gene implicated in this production was cloned and expressed, and the expressed enzyme was purified. The product obtained by the reaction of the purified enzyme with linoleic acid was identified as 8R,11S-dihydroxy-9,12(Z,Z)-octadecadienoic acid (8R,11S-DiHODE). The catalytic efficiency of this enzyme toward linoleic acid was the highest among the unsaturated fatty acids tested, indicating that this enzyme was a novel 8R,11S-linoleate diol synthase (8R,11S-LDS). A sexual stage in the life cycle of P. chrysogenum has recently been discovered, and 8R,11S-DiHODE produced by 8R,11S-LDS may constitute a precocious sexual inducer factor, responsible for regulating the sexual and asexual cycles of this fungus.

Discovery of a Novel Linoleate Dioxygenase of Fusarium oxysporum and Linoleate Diol Synthase of Colletotrichum graminicola

Fungal pathogens constitute serious threats for many forms of life. The pathogenic fungi Fusarium and Colletotrichum and their formae speciales (f. spp.) infect many types of crops with severe consequences and Fusarium oxysporum can also induce keratitis and allergic conditions in humans. These fungi code for homologues of dioxygenase-cytochrome P450 (DOX-CYP) fusion proteins of the animal heme peroxidase (cyclooxygenase) superfamily. The objective was to characterize the enzymatic activities of the DOX-CYP homologue of Colletotrichum graminicola (EFQ34869) and the DOX homologue of F. oxysporum (EGU79548). The former oxidized oleic and linoleic acids in analogy with 7,8-linoleate diol synthases (LDSs), but with the additional biosynthesis of 8,11-dihydroxylinoleic acid. The latter metabolized fatty acids to hydroperoxides with broad substrate specificity. It oxidized 20:4n-6 and 18:2n-6 to hydroperoxides with an R configuration at the (n-10) positions, and other n-6 fatty acids in the same way. [11S-(2)H]18:2n-6 was oxidized with retention and [11R-(2)H]18:2n-6 with loss of deuterium, suggesting suprafacial hydrogen abstraction and oxygen insertion. Fatty acids of the n-3 series were oxidized less efficiently and often to hydroperoxides with an R configuration at both (n-10) and (n-7) positions. The enzyme spans 1426 amino acids with about 825 residues in the N-terminal domain with DOX homology and 600 residues at the C-terminal domain without homology to other enzymes. We conclude that fungal oxylipins can be formed by two novel subfamilies of cyclooxygenase-related DOX.

In Silico/In Vivo Insights into the Functional and Evolutionary Pathway of Pseudomonas aeruginosa Oleate-Diol Synthase. Discovery of a New Bacterial Di-Heme Cytochrome C Peroxidase Subfamily

As previously reported, P. aeruginosa genes PA2077 and PA2078 code for 10S-DOX (10S-Dioxygenase) and 7,10-DS (7,10-Diol Synthase) enzymes involved in long-chain fatty acid oxygenation through the recently described oleate-diol synthase pathway. Analysis of the amino acid sequence of both enzymes revealed the presence of two heme-binding motifs (CXXCH) on each protein. Phylogenetic analysis showed the relation of both proteins to bacterial di-heme cytochrome c peroxidases (Ccps), similar to Xanthomonas sp. 35Y rubber oxidase RoxA. Structural homology modelling of PA2077 and PA2078 was achieved using RoxA (pdb 4b2n) as a template. From the 3D model obtained, presence of significant amino acid variations in the predicted heme-environment was found. Moreover, the presence of palindromic repeats located in enzyme-coding regions, acting as protein evolution elements, is reported here for the first time in P. aeruginosa genome. These observations and the constructed phylogenetic tree of the two proteins, allow the proposal of an evolutionary pathway for P. aeruginosa oleate-diol synthase operon. Taking together the in silico and in vivo results obtained we conclude that enzymes PA2077 and PA2078 are the first described members of a new subfamily of bacterial peroxidases, designated as Fatty acid-di-heme Cytochrome cperoxidases (FadCcp).

Bacterial and algal orthologs of prostaglandin H₂synthase: novel insights into the evolution of an integral membrane protein

Prostaglandin H₂synthase (PGHS; EC 1.14.99.1), a bi-functional heme enzyme that contains cyclooxygenase and peroxidase activities, plays a central role in the inflammatory response, pain, and blood clotting in higher eukaryotes. In this review, we discuss the progenitors of the mammalian enzyme by using modern bioinformatics and homology modeling to draw comparisons between this well-studied system and its orthologs from algae and bacterial sources. A clade of bacterial and algal orthologs is described that have salient structural features distinct from eukaryotic counterparts, including the lack of a dimerization and EGF-like domains, the absence of gene duplicates, and minimal membrane-binding domains. The functional implications of shared and variant features are discussed.

Production of 5,8-dihydroxy-9,12(Z,Z)-octadecadienoic acid from linoleic acid by whole recombinant Escherichia coli cells expressing diol synthase from Aspergillus nidulans

Diol synthase from Aspergillus nidulans was cloned and expressed in Escherichia coli. Recombinant E. coli cells expressing diol synthase from A. nidulans converted linoleic acid to a product that was identified as 5,8-dihydroxy-9,12(Z,Z)-octadecadienoic acid by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). The recombinant cells and the purified enzyme showed the highest activity for linoleic acid among the fatty acids tested. The optimal reaction conditions for the production of 5,8-dihydroxy-9,12(Z,Z)-octadecadienoic acid from linoleic acid using whole recombinant E. coli cells expressing diol synthase were pH 7.5, 35°C, 250 rpm, 5 g l(-1) linoleic acid, 23 g l(-1) cells, and 20% (v/v) dimethyl sulfoxide in a 250-ml baffled flask. Under these optimized conditions, whole recombinant cells expressing diol synthase produced 4.98 g l(-1) 5,8-dihydroxy-9,12(Z,Z)-octadecadienoic acid for 150 min without detectable byproducts, with a conversion yield of 99% (w/w) and a productivity of 2.5 g l(-1) h(-1). This is the first report on the biotechnological production of dihydroxy fatty acid using whole recombinant cells expressing diol synthase.

Discovery of a linoleate 9S-dioxygenase and an allene oxide synthase in a fusion protein of Fusarium oxysporum

Fusarium oxysporum is a devastating plant pathogen that oxidizes C₁₈ fatty acids sequentially to jasmonates. The genome codes for putative dioxygenase (DOX)-cytochrome P450 (CYP) fusion proteins homologous to linoleate diol synthases (LDSs) and the allene oxide synthase (AOS) of Aspergillus terreus, e.g., FOXB_01332. Recombinant FOXB_01332 oxidized 18:2n-6 to 9S-hydroperoxy-10(E),12(Z)-octadecadienoic acid by hydrogen abstraction and antarafacial insertion of molecular oxygen and sequentially to an allene oxide, 9S(10)-epoxy-10,12(Z)-octadecadienoic acid, as judged from nonenzymatic hydrolysis products (α- and γ-ketols). The enzyme was therefore designated 9S-DOX-AOS. The 9S-DOX activity oxidized C₁₈ and C₂₀ fatty acids of the n-6 and n-3 series to hydroperoxides at the n-9 and n-7 positions, and the n-9 hydroperoxides could be sequentially transformed to allene oxides with only a few exceptions. The AOS activity was stereospecific for 9- and 11-hydroperoxides with S configurations. FOXB_01332 has acidic and alcoholic residues, Glu⁹⁴⁶-Val-Leu-Ser⁹⁴⁹, at positions of crucial Asn and Gln residues (Asn-Xaa-Xaa-Gln) of the AOS and LDS. Site-directed mutagenesis studies revealed that FOXB_01332 and AOS of A. terreus differ in catalytically important residues suggesting that AOS of A. terreus and F. oxysporum belong to different subfamilies. FOXB_01332 is the first linoleate 9-DOX with homology to animal heme peroxidases and the first 9-DOX-AOS fusion protein.

7,8- and 5,8-Linoleate diol synthases support the heterolytic scission of oxygen-oxygen bonds by different amide residues

Linoleate diol synthases (LDS) are fungal dioxygenase-cytochrome P450 fusion enzymes. They oxidize 18:2n-6 sequentially to 8R-hydroperoxylinoleic acid (8R-HPODE) and 7S,8S- or 5S,8R-dihydroxylinoleic acids (DiHODE) by intramolecular oxygen transfer. The P450 domains contain a conserved sequence, Ala-Asn-Gln-Xaa-Gln, presumably located in the I-helices. The Asn938Leu replacement of 7,8-LDS of Gaeumannomyces graminis virtually abolished and the Asn938Asp and Asn938Gln replacements reduced the hydroperoxide isomerase activity. Gln941Leu and Gln941Glu substitutions had little effects. Replacements of the homologous Asn(887) and Gln(890) residues of 5,8-LDS of Aspergillus fumigatus yielded the opposite results. Asn887Leu and Asn887Gln of 5,8-LDS retained 5,8-DiHODE as the main metabolite with an increased formation of 6,8- and 8,11-DiHODE, whereas Gln890Leu almost abolished the 5,8-LDS activity. Replacement of Gln(890) with Glu also retained 5,8-DiHODE as the main product, but shifted oxygenation from C-5 to C-7 and C-11 and to formation of epoxyalcohols by homolytic scission of 8R-HPODE. P450 hydroxylases usually contain an "acid-alcohol" pair in the I-helices for the heterolytic scission of O2 and formation of compound I (Por(+) Fe(IV)=O) and water. The function of the acid-alcohol pair appears to be replaced by two different amide residues, Asn(938) of 7,8-LDS and Gln(890) of 5,8-LDS, for heterolysis of 8R-HPODE to generate compound I.

Production of hydroxy fatty acids by microbial fatty acid-hydroxylation enzymes

Hydroxy fatty acids are widely used in chemical, food, and cosmetic industries as starting materials for the synthesis of polymers and as additives for the manufacture of lubricants, emulsifiers, and stabilizers. They have antibiotic, anti-inflammatory, and anticancer activities and therefore can be applied for medicinal uses. Microbial fatty acid-hydroxylation enzymes, including P450, lipoxygenase, hydratase, 12-hydroxylase, and diol synthase, synthesize regio-specific hydroxy fatty acids. In this article, microbial fatty acid-hydroxylation enzymes, with a focus on region-specificity and diversity, are summarized and the production of mono-, di-, and tri-hydroxy fatty acids is introduced. Finally, the production methods of regio-specific and diverse hydroxy fatty acids, such as gene screening, protein engineering, metabolic engineering, and combinatory biosynthesis, are suggested.

Expression of fusion proteins of Aspergillus terreus reveals a novel allene oxide synthase

Aspergilli oxidize C18 unsaturated fatty acids by dioxygenase-cytochrome P450 fusion proteins to signal molecules involved in reproduction and host-pathogen interactions. Aspergillus terreus expresses linoleate 9R-dioxygenase (9R-DOX) and allene oxide synthase (AOS) activities in membrane fractions. The genome contains five genes (ATEG), which may code for a 9R-DOX-AOS fusion protein. The genes were cloned and expressed, but none of them oxidized 18:2n-6 to 9R-hydroperoxy-10(E),12(Z)-octadecadienoic acid (9R-HPODE). ATEG_02036 transformed 9R-HPODE to an unstable allene oxide, 9(R),10-epoxy-10,12(Z)-octadecadienoic acid. A substitution in the P450 domain (C1073S) abolished AOS activity. The N964V and N964D mutants both showed markedly reduced AOS activity, suggesting that Asn(964) may facilitate homolytic cleavage of the dioxygen bond of 9R-HPODE with formation of compound II in analogy with plant AOS (CYP74) and prostacyclin synthase (CYP8A1). ATEG_03992 was identified as 5,8-linoleate diol synthase (5,8-LDS). Replacement of Asn(878) in 5,8-LDS with leucine (N878L) mainly shifted ferryl oxygen insertion from C-5 toward C-6, but replacements of Gln(881) markedly affected catalysis. The Q881L mutant virtually abolished the diol synthase activity. Replacement of Gln(881) with Asn, Glu, Asp, or Lys residues augmented the homolytic cleavage of 8R-HPODE with formation of 10-hydroxy-8(9)-epoxy-12(Z)-octadecenoic acid (erythro/threo, 1-4:1) and/or shifted ferryl oxygen insertion from C-5 toward C-11. We conclude that homolysis and heterolysis of the dioxygen bond with formation of compound II in AOS and compound I in 5,8-LDS are influenced by Asn and Gln residues, respectively, of the I-helices. AOS of A. terreus appears to have evolved independently of CYP74 but with an analogous reaction mechanism.

Novel insights into cyclooxygenases, linoleate diol synthases, and lipoxygenases from deuterium kinetic isotope effects and oxidation of substrate analogs

Cyclooxygenases (COX) and 8R-dioxygenase (8R-DOX) activities of linoleate diol synthases (LDS) are homologous heme-dependent enzymes that oxygenate fatty acids by a tyrosyl radical-mediated hydrogen abstraction and antarafacial insertion of O(2). Soybean lipoxygenase-1 (sLOX-1) contains non-heme iron and oxidizes 18:2n-6 with a large deuterium kinetic isotope effect (D-KIE). The aim of the present work was to obtain further mechanistic insight into the action of these enzymes by using a series of n-6 and n-9 fatty acids and by analysis of D-KIE. COX-1 oxidized C(20) and C(18) fatty acids in the following order of rates: 20:2n-6>20:1n-6>20:3n-9>20:1n-9 and 18:3n-3≥18:2n-6>18:1n-6. 18:2n-6 and its geometrical isomer (9E,12Z)18:2 were both mainly oxygenated at C-9 by COX-1, but the 9Z,12E isomer was mostly oxygenated at C-13. A cis-configured double bond in the n-6 position therefore seems important for substrate positioning. 8R-DOX oxidized (9Z,12E)18:2 at C-8 in analogy with 18:2n-6, but the 9E,12Z isomer was mainly subject to hydrogen abstraction at C-11 and oxygen insertion at C-9 by 8R-DOX of 5,8-LDS. sLOX-1 and 13R-MnLOX oxidized [11S-(2)H]18:2n-6 with similar D-KIE (~53), which implies that the catalytic metals did not alter the D-KIE. Oxygenation of 18:2n-6 by COX-1 and COX-2 took place with a D-KIE of 3-5 as probed by incubations of [11,11-(2)H(2)]- and [11S-(2)H]18:2n-6. In contrast, the more energetically demanding hydrogen abstractions of the allylic carbons of 20:1n-6 by COX-1 and 18:1n-9 by 8R-DOX were both accompanied by large D-KIE (>20).

The fatty acid 8,11-diol synthase of Aspergillus fumigatus is inhibited by imidazole derivatives and unrelated to PpoB

(8R)-Hydroperoxy-(9Z,12Z)-octadecadienoic acid (8-HPODE) is formed by aspergilli as an intermediate in biosynthesis of oxylipins with effects on sporulation. 8-HPODE is transformed by separate diol synthases to (5S,8R)-dihydroxy- and (8R,11S)-dihydroxy-(9Z,12Z)-octadecadienoic acids (5,8- and 8,11-DiHODE). The former is formed by the cytochrome P450 (P450) domain of 5,8-linoleate diol synthase (5,8-LDS or PpoA). Our aim was to characterize the 8,11-diol synthase of Aspergillus fumigatus, which is prominent in many strains. The 8,11-diol synthase was soluble and had a larger molecular size (>100 kDa) than most P450. Miconazole, ketoconazole, and 1-benzylimidazole, classical inhibitors of P450, reduced the biosynthesis of 8,11-DiHODE from 8-HPODE (apparent IC(50) values ~0.8, ~5, and ~0.6 μM, respectively), but did not inhibit the biosynthesis of 5,8-DiHODE. Analysis of hydroperoxides of regioisomeric C(18) and C(20) fatty acids showed that the 8,11-diol synthase was specific for certain hydroperoxides with R configuration. The suprafacial hydrogen abstraction and oxygen insertion at C-11 of 8-HPODE was associated with a small deuterium kinetic isotope effect ((H) k (cat)/(D) k (cat) ~1.5), consistent with P450-catalyzed oxidation. The genome of A. fumigatus contains over 70 P450 sequences. The reaction mechanism, size, and solubility of 8,11-diol synthase pointed to PpoB, a homologue of 5,8-LDS, as a possible candidate of this activity. Gene deletion of ppoB of A. fumigatus strains AF:∆ku80 and J272 did not inhibit biosynthesis of 8,11-DiHODE and recombinant PpoB appeared to lack diol synthase activity. We conclude that 8,11-DiHODE is formed from 8-HPODE by a soluble and substrate-specific 8,11-diol synthase with catalytic characteristics of class III P450.

Linolenate 9R-dioxygenase and allene oxide synthase activities of Lasiodiplodia theobromae

Jasmonic acid (JA) is synthesized from linolenic acid (18:3n-3) by sequential action of 13-lipoxygenase, allene oxide synthase (AOS), and allene oxide cyclase. The fungus Lasiodiplodia theobromae can produce large amounts of JA and was recently reported to form the JA precursor 12-oxophytodienoic acid. The objective of our study was to characterize the fatty acid dioxygenase activities of this fungus. Two strains of L. theobromae with low JA secretion (~0.2 mg/L medium) oxygenated 18:3n-3 to 5,8-dihydroxy-9Z,12Z,15Z-octadecatrienoic acid as well as 9R-hydroperoxy-10E,12Z,15Z-octadecatrienoic acid, which was metabolized by an AOS activity into 9-hydroxy-10-oxo-12Z,15Z-octadecadienoic acid. Analogous conversions were observed with linoleic acid (18:2n-6). Studies using [11S-(2)H]18:2n-6 revealed that the putative 9R-dioxygenase catalyzed stereospecific removal of the 11R hydrogen followed by suprafacial attack of dioxygen at C-9. Mycelia from these strains of L. theobromae contained 18:2n-6 as the major polyunsaturated acid but lacked 18:3n-3. A third strain with a high secretion of JA (~200 mg/L) contained 18:3n-3 as a major fatty acid and produced 5,8-dihydroxy-9Z,12Z,15Z-octadecatrienoic acid from added 18:3n-3. This strain also lacked the JA biosynthetic enzymes present in higher plants.

Stereoselective oxidation of regioisomeric octadecenoic acids by fatty acid dioxygenases

Seven Z-octadecenoic acids having the double bond located in positions 6Z to 13Z were photooxidized. The resulting hydroperoxy-E-octadecenoic acids [HpOME(E)] were resolved by chiral phase-HPLC-MS, and the absolute configurations of the enantiomers were determined by gas chromatographic analysis of diastereoisomeric derivatives. The MS/MS/MS spectra showed characteristic fragments, which were influenced by the distance between the hydroperoxide and carboxyl groups. These fatty acids were then investigated as substrates of cyclooxygenase-1 (COX-1), manganese lipoxygenase (MnLOX), and the (8R)-dioxygenase (8R-DOX) activities of two linoleate diol synthases (LDS) and 10R-DOX. COX-1 and MnLOX abstracted hydrogen at C-11 of (12Z)-18:1 and C-12 of (13Z)-18:1. (11Z)-18:1 was subject to hydrogen abstraction at C-10 by MnLOX and at both allylic positions by COX-1. Both allylic hydrogens of (8Z)-18:1 were also abstracted by 8R-DOX activities of LDS and 10R-DOX, but only the allylic hydrogens close to the carboxyl groups of (11Z)-18:1 and (12Z)-18:1. 8R-DOX also oxidized monoenoic C(14)-C(20) fatty acids with double bonds at the (9Z) position, suggesting that the length of the omega end has little influence on positioning for oxygenation. We conclude that COX-1 and MnLOX can readily abstract allylic hydrogens of octadecenoic fatty acids from C-10 to C-12 and 8R-DOX from C-7 and C-12.