8R-Lipoxygenase-catalyzed synthesis of a prominent cis-epoxyalcohol from dihomo-γ-linolenic acid: a distinctive transformation compared with S-lipoxygenases

The versatile CYP74 clan enzyme CYP440A19 from the European lancelet Branchiostoma lanceolatum biosynthesizes novel macrolactone, epoxydiene, and related oxylipins

The present work reports the detection and cloning of a new CYP74 clan gene of the European lancelet (Branchiostoma lanceolatum) and the biochemical characterization of the recombinant protein CYP440A19. CYP440A19 possessed epoxyalcohol synthase (EAS) activity towards the 13-hydroperoxides of linoleic and α-linolenic acids, which were converted into oxiranylcarbinols, i.e., (11S,12R,13S)-11-hydroxy-12,13-epoxy derivatives. The conversion of 9-hydroperoxides produced distinct products. Linoleic acid 9(S)-hydroperoxide (9-HPOD) was mainly converted into 9,14-diol (10E,12E)-9,14-dihydroxy-10,12-octadecadienoic acid and macrolactone 9(S),10(R)-epoxy-11(E)-octadecen-13(S)-olide. In addition, (8Z)-colneleic acid was formed. Brief incubations of the enzyme with 9-HPOD in a biphasic system of hexane-water enabled the isolation of the short-lived 9,10-epoxydiene (9S,10R,11E,13E)-9,10-epoxy-11,13-octadecadienoic acid. The structure and stereochemistry of the epoxyalcohols, macrolactone, (8Z)-colneleic acid (Me), and 9,10-epoxydiene (Me) were confirmed by 1H-NMR, 1H-1H-COSY, 1H-13C-HSQC, and 1H-13C-HMBC spectroscopy. Macrolactone and cis-9,10-epoxydiene are novel products. The 9-hydroperoxide of α-linolenic acid was mainly converted into macrolactone 9(S),10(R)-epoxy-11(E),15(Z)-octadecadiene-13(S)-olide and a minority of divinyl ethers, particularly (8Z)-colnelenic acid. The versatility of enzyme catalysis, as well as the diversity of CYP74s and other enzymes involved in oxylipin biosynthesis, demonstrates the complexity of the lipoxygenase pathway in lancelets.

Epoxyalcohol Synthase Branch of Lipoxygenase Cascade

Oxylipins are one of the most important classes of bioregulators, biosynthesized through the oxidative metabolism of unsaturated fatty acids in various aerobic organisms. Oxylipins are bioregulators that maintain homeostasis at the cellular and organismal levels. The most important oxylipins are mammalian eicosanoids and plant octadecanoids. In plants, the main source of oxylipins is the lipoxygenase cascade, the key enzymes of which are nonclassical cytochromes P450 of the CYP74 family, namely allene oxide synthases (AOSs), hydroperoxide lyases (HPLs), and divinyl ether synthases (DESs). The most well-studied plant oxylipins are jasmonates (AOS products) and traumatin and green leaf volatiles (HPL products), whereas other oxylipins remain outside of the focus of researchers' attention. Among them, there is a large group of epoxy hydroxy fatty acids (epoxyalcohols), whose biosynthesis has remained unclear for a long time. In 2008, the first epoxyalcohol synthase of lancelet Branchiostoma floridae, BfEAS (CYP440A1), was discovered. The present review collects data on EASs discovered after BfEAS and enzymes exhibiting EAS activity along with other catalytic activities. This review also presents the results of a study on the evolutionary processes possibly occurring within the P450 superfamily as a whole.

Lipoxygenases and Lipoxygenase Products in Marine Diatoms

Marine diatoms negatively affect reproduction and later larval development of dominant zooplankton grazers such as copepods, thereby lowering the recruitment of the next generations of these small crustaceans that are a major food source for larval fish species. The phenomenon has been explained in terms of chemical defense due to grazer-induced synthesis of oxylipins, lipoxygenase-derived oxygenated fatty acid derivatives. Since this first report, studies about diatom oxylipins have multiplied and broadened toward other aspects concerning bloom dynamics, cell growth, and cell differentiation. Diatom oxylipins embrace a number of diverse structures that are recognized as chemical signals in ecological and physiological processes in many other organisms. In diatoms, the most studied examples include polyunsaturated aldehydes (PUAs) and nonvolatile oxylipins (NVOs). The purpose of this chapter is to provide the analytical tools to deal with identification, analysis and biosynthesis of these compounds. Emphasis is given to identification of the enzymatic steps and characterization of the species-specific lipoxygenases even in absence of the availability of molecular information.

Identification of CYP443D1 (CYP74 clan) of Nematostella vectensis as a first cnidarian epoxyalcohol synthase and insights into its catalytic mechanism

The CYP74 clan enzymes are responsible for the biosynthesis of numerous bioactive oxylipins in higher plants, some Proteobacteria, brown and green algae, and Metazoa. A novel putative CYP74 clan gene CYP443D1 of the starlet sea anemone (Nematostella vectensis, Cnidaria) has been cloned, and the properties of the corresponding recombinant protein have been studied in the present work. The recombinant CYP443D1 was incubated with the 9- and 13-hydroperoxides of linoleic and α-linolenic acids (9-HPOD, 13-HPOD, 9-HPOT, and 13-HPOT, respectively), as well as with the 9-hydroperoxide of γ-linolenic acid (γ-9-HPOT) and 15-hydroperoxide of eicosapentaenoic acid (15-HPEPE). The enzyme was active towards all C₁₈-hydroperoxides with some preference to 9-HPOD. In contrast, 15-HPEPE was a poor substrate. The CYP443D1 specifically converted 9-HPOD into the oxiranyl carbinol 1, (9S,10R,11S,12Z)-9,10-epoxy-11-hydroxy-12-octadecenoic acid. Both ¹⁸O atoms from [¹⁸O₂-hydroperoxy]9-HPOD were virtually quantitatively incorporated into product 1. Thus, the CYP443D1 exhibited epoxyalcohol synthase (EAS) activity. The ¹⁸O labelling data demonstrated that the reaction mechanism included three sequential steps: (1) hydroperoxyl homolysis, (2) oxy radical rearrangement into epoxyallylic radical, (3) hydroxyl rebound, resulting in oxiranyl carbinol formation. The 9-HPOT and γ-9-HPOT were also specifically converted into the oxiranyl carbinols, 15,16- and 6,7-dehydro analogues of compound 1, respectively. The 13-HPOD was converted into erythro- and threo-isomers of oxiranyl carbinol, as well as oxiranyl vinyl carbinols. The obtained results allow assignment of the name "N. vectensis EAS" (NvEAS) to CYP443D1. The NvEAS is a first EAS detected in Cnidaria.

Oxylipin diversity in the diatom family Leptocylindraceae reveals DHA derivatives in marine diatoms

Marine planktonic organisms, such as diatoms, are prospective sources of novel bioactive metabolites. Oxygenated derivatives of fatty acids, generally referred to as oxylipins, in diatoms comprise a highly diverse and complex family of secondary metabolites. These molecules have recently been implicated in several biological processes including intra- and inter-cellular signaling as well as in defense against biotic stressors and grazers. Here, we analyze the production and diversity of C₂₀ and C₂₂ non-volatile oxylipins in five species of the family Leptocylindraceae, which constitute a basal clade in the diatom phylogeny. We report the presence of species-specific lipoxygenase activity and oxylipin patterns, providing the first demonstration of enzymatic production of docosahexaenoic acid derivatives in marine diatoms. The differences observed in lipoxygenase pathways among the species investigated broadly reflected the relationships observed with phylogenetic markers, thus providing functional support to the taxonomic diversity of the individual species.

Demonstration of HNE-related aldehyde formation via lipoxygenase-catalyzed synthesis of a bis-allylic dihydroperoxide intermediate

One of the proposed pathways to the synthesis of 4-hydroxy-nonenal (HNE) and related aldehydes entails formation of an intermediate bis-allylic fatty acid dihydroperoxide. As a first direct demonstration of such a pathway and proof of principle, herein we show that 8R-lipoxygenase (8R-LOX) catalyzes the enzymatic production of the HNE-like product (11-oxo-8-hydroperoxy-undeca-5,9-dienoic acid) via synthesis of 8,11-dihydroperoxy-eicosa-5,9,12,14-tetraenoic acid intermediate. Incubation of arachidonic acid with 8R-LOX formed initially 8R-hydroperoxy-eicosatetraenoic acid (8R-HPETE), which was further converted to a mixture of products including a prominent HPNE-like enone. A new bis-allylic dihydroperoxide was trapped when the incubation was repeated on ice. Reincubation of this intermediate with 8R-LOX successfully demonstrated its conversion to the enone products, and this reaction was greatly accelerated by coincubation with NDGA, a reductant of the LOX iron. These findings identify a plausible mechanism that could contribute to the production of 4-hydroxy-alkenals in vivo.

Secretion of two novel enzymes, manganese 9S-lipoxygenase and epoxy alcohol synthase, by the rice pathogen Magnaporthe salvinii

The mycelium of the rice stem pathogen, Magnaporthe salvinii, secreted linoleate 9S-lipoxygenase (9S-LOX) and epoxy alcohol synthase (EAS). The EAS rapidly transformed 9S-hydroperoxy-octadeca-10E,12Z-dienoic acid (9S-HPODE) to threo 10 (11)-epoxy-9S-hydroxy-12Z-octadecenoic acid, but other hydroperoxy FAs were poor substrates. 9S-LOX was expressed in Pichia pastoris. Recombinant 9S-LOX oxidized 18:2n-6 directly to 9S-HPODE, the end product, and also to two intermediates, 11S-hydroperoxy-9Z,12Z-octadecenoic acid (11S-HPODE; ∼5%) and 13R-hydroperoxy-9Z,11E-octadecadienoic acid (13R-HPODE; ∼1%). 11S- and 13R-HPODE were isomerized to 9S-HPODE, probably after oxidation to peroxyl radicals, β-fragmentation, and oxygen insertion at C-9. The 18:3n-3 was oxidized at C-9, C-11, and C-13, and to 9,16-dihydroxy-10E,12,14E-octadecatrienoic acid. 9S-LOX contained catalytic manganese (Mn:protein ∼0.2:1; Mn/Fe, 1:0.05), and its sequence could be aligned with 77% identity to 13R-LOX with catalytic manganese lipoxygenase (13R-MnLOX) of the Take-all fungus. The Leu350Met mutant of 9S-LOX shifted oxidation of 18:2n-6 from C-9 to C-13, and the Phe347Leu, Phe347Val, and Phe347Ala mutants of 13R-MnLOX from C-13 to C-9. In conclusion, M. salvinii secretes 9S-LOX with catalytic manganese along with a specific EAS. Alterations in the Sloane determinant of 9S-LOX and 13R-MnLOX with larger and smaller hydrophobic residues interconverted the regiospecific oxidation of 18:2n-6, presumably by altering the substrate position in relation to oxygen insertion.