Structure and biosynthesis of marine algal oxylipins

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

The Perspective of Diagnostic and Prognostic Values of Lipoxygenases mRNA Expression in Colon Adenocarcinoma

Background

This study was mainly to explore and study the potential application of lipoxygenases (ALOX) family genes in the diagnostic and prognostic values of colon adenocarcinoma (COAD).

Methods

Data sets related to the ALOX genes of COAD were obtained from The Cancer Genome Atlas and the University of California, Santa Cruz Xena browser. Then, the relevant biological information was downloaded from the public data platform. Finally, the bioinformatics technologies and clinical verification were employed to comprehensively analyze the potential values of ALOX genes.

Results

The Pearson correlation analysis indicated that there were correlations among ALOXE3, ALOX5, ALOX12, and ALOX12B. The diagnostic receiver operating characteristic (ROC) curves suggested that ALOXE3 and ALOX12 had significant diagnosis in COAD: ALOXE3; P<0.001, area under curve (AUC) 95%CI:=0.818 (0.773–0.862) and ALOX12; P<0.001, AUC 95%CI=0.774 (0.682–0.807). Besides, the verification study indicated that ALOX12 had a diagnostic value in COAD. Finally, our multivariate survival analysis and comprehensive prognosis of ALOX genes in COAD suggested that the ALOXE3 and ALOX12 were associated with COAD overall survival: ALOXE3; P=0.025, HR 95%CI=1.765 (1.074–2.901), ALOX12; P=0.046, HR 95%CI=1.680 (1.009–2.796), and the low expression of ALOXE3 and ALOX12 had a favorable prognosis of COAD (all P<0.05); on the contrary, the high regulation of them increased the risk of death.

Conclusion

In our study, we observed that the mRNA expressions of ALOX genes were associated with the diagnosis and prognosis of COAD. The results of the diagnostic analysis suggested that ALOX12 might have a diagnosis value in COAD. Besides, our comprehensive prognosis analysis indicated that ALOXE3 combined ALOX12 might serve as potential prognosis biomarkers for COAD.

Mammalian-Like Inflammatory and Pro-Resolving Oxylipins in Marine Algae

Oxylipins constitute a family of oxidized fatty acids, that are well known as tissue hormones in mammals. They contribute to inflammation and its resolution. The major classes of these lipid mediators are inflammatory prostaglandins (PGs) and leukotrienes (LTs) as well as pro-resolving resolvins (Rvs). Understanding their biosynthetic pathways and modes of action is important for anti-inflammatory interventions. Besides mammals, marine algae also biosynthesize mammalian-like oxylipins and thus offer new opportunities for oxylipin research. They provide prolific sources for these compounds and offer unique opportunities to study alternative biosynthetic pathways to the well-known lipid mediators. Herein, we discuss recent findings on the biosynthesis of oxylipins in mammals and algae including an alternative pathway to prostaglandin E2 , a novel pathway to a precursor of leukotriene B4 , and the production of resolvins in algae. We evaluate the pharmacological potential of the algal metabolites with implications in health and disease.

Anti-inflammatory Activity of Bioactive Compounds from Microalgae and Cyanobacteria by Focusing on the Mechanisms of Action

Microalgae and cyanobacteria are the potentially valuable source of bioactive compounds applied in the various industries and human usage in different fields of pharmaceutical, nutraceutical, and cosmetic disciplines. One of the interesting aspects is their application as the anti-inflammatory agents for treatment of inflammation related mal-conditions. Natural compounds are of great importance in the treatment of inflammations to reduce the reaction of immune system against pathogens, toxic compounds and damaged cells. A wide range of different metabolites with various chemical structures, including small molecules and peptides and proteins, polysaccharides, fatty acids and their derivatives have been found in microalgae and cyanobacteria which have anti-inflammatory activity. In this review, we summarized different metabolites with anti-inflammatory activity that were extracted from these microorganisms and their mechanisms. The bioactive compounds from microalgae and cyanobacteria have exhibited anti-inflammatory activity through different mechanisms acting intra- or extra- cellularly. So, they could be considered as promising anti-inflammatory agents in treatment of related diseases.

Characterization of Differential Dynamics, Specificity, and Allostery of Lipoxygenase Family Members

Accurate modeling of structural dynamics of proteins and their differentiation across different species can help us understand generic mechanisms of function shared by family members and the molecular basis of the specificity of individual members. We focused here on the family of lipoxygenases, enzymes that catalyze lipid oxidation, the mammalian and bacterial structures of which have been elucidated. We present a systematic method of approach for characterizing the sequence, structure, dynamics, and allosteric signaling properties of these enzymes using a combination of structure-based models and methods and bioinformatics tools applied to a data set of 88 structures. The analysis elucidates the signature dynamics of the lipoxygenase family and its differentiation among members, as well as key sites that enable its adaptation to specific substrate binding and allosteric activity.

1-Octen-3-ol, a self-stimulating oxylipin messenger, can prime and induce defense of marine alga

BACKGROUND

Short chain oxylipins in plants as the main volatile organic carbon have been speculated to playing an important role for plant innate immunity, however, not yet intensively studied and far away established as the fully recognized algae defense signals.

RESULTS

The production of 1-octen-3-ol is self-amplified via the fatty acid-oxylipin metabolic cycle through positive feedback loop. Production of 1-octen-3-ol may act as a messenger that induces P. haitanensis to be in a "primed" state and ready for defense by upregulating the synthesis of methyl jasmonic acid, indole-3-acetic acid, and gibberellin A3. Production of these oxylipins also adjust the redox state in cells, resulting in host defense activation.

CONCLUSIONS

We provide the first demonstration that 1-octen-3-ol from P. haitanensis, can act as a self-stimulating community messenger. The multiple effects of 1-octen-3-ol may explain why P. haitanensis, a very ancient lineage within plant kingdom, thrives in the niche of intertidal zones.

Fundamental Insights into Proton-Coupled Electron Transfer in Soybean Lipoxygenase from Quantum Mechanical/Molecular Mechanical Free Energy Simulations

The proton-coupled electron transfer (PCET) reaction catalyzed by soybean lipoxygenase has served as a prototype for understanding hydrogen tunneling in enzymes. Herein this PCET reaction is studied with mixed quantum mechanical/molecular mechanical (QM/MM) free energy simulations. The free energy surfaces are computed as functions of the proton donor-acceptor (C-O) distance and the proton coordinate, and the potential of mean force is computed as a function of the C-O distance, inherently including anharmonicity. The simulation results are used to calculate the kinetic isotope effects for the wild-type enzyme (WT) and the L546A/L754A double mutant (DM), which have been measured experimentally to be ∼80 and ∼700, respectively. The PCET reaction is found to be exoergic for WT and slightly endoergic for the DM, and the equilibrium C-O distance for the reactant is found to be ∼0.2 Å greater for the DM than for WT. The larger equilibrium distance for the DM, which is due mainly to less optimal substrate binding in the expanded binding cavity, is primarily responsible for its higher kinetic isotope effect. The calculated potentials of mean force are anharmonic and relatively soft at shorter C-O distances, allowing efficient thermal sampling of the shorter distances required for effective hydrogen tunneling. The primarily local electrostatic field at the transferring hydrogen is ∼100 MV/cm in the direction to facilitate proton transfer and increases dramatically as the C-O distance decreases. These simulations suggest that the overall protein environment is important for conformational sampling of active substrate configurations aligned for proton transfer, but the PCET reaction is influenced primarily by local electrostatic effects that facilitate conformational sampling of shorter proton donor-acceptor distances required for effective hydrogen tunneling.

Oxylipins in the spikemoss Selaginella martensii: Detection of divinyl ethers, 12-oxophytodienoic acid and related cyclopentenones

Green tissues of spikemoss Selaginella martensii Spring possessed the complex oxylipins patterns. Major oxylipins were the products of linoleic and α-linolenic acids metabolism via the sequential action of 13-lipoxygenase and divinyl ether synthase (DES) or allene oxide synthase (AOS). AOS products were represented by 12-oxophytodienoic acid (12-oxo-PDA) isomers. Exceptionally, S. martensii possesses high level of 12-oxo-9(13),15-PDA, which is very uncommon in flowering plants. Separate divinyl ethers were purified after micro-preparative incubations of linoleic or α-linolenic acids with homogenate of S. martensii aerial parts. The NMR data allowed us to identify all geometric isomers of divinyl ethers. Linoleic acid was converted to divinyl ethers etheroleic acid, (11Z)-etheroleic acid and a minority of (ω5Z)-etheroleic acid. With α-linolenate precursor, the specificity of divinyl ether biosynthesis was distinct. Etherolenic and (ω5Z)-etherolenic acids were the prevailing products while (11Z)-etherolenic acid was a minor one. Divinyl ethers are detected first time in non-flowering land plant. These are the first observations of fatty acid metabolism through the lipoxygenase pathway in spikemosses (Lycopodiophyta).

Extraction and Analysis of Oxylipins from Macroalgae Illustrated on the Example Gracilaria vermiculophylla

Oxylipins are natural products that are derived by oxidative transformations of unsaturated fatty acids. These metabolites are found in a wide range of organisms from the animal kingdom to plants and algae. They represent an important class of signaling molecules, mediating intra- and intercellular processes such as development, inflammation, and other stress responses. In addition, these metabolites directly function as chemical defense against grazers and pathogens. In the red alga Gracilaria vermiculophylla, oxylipin production is initiated by mechanical tissue disruption and can also be induced in intact algae in response to external stress signals. The defense metabolites mostly result from the lipase- and lipoxygenase-mediated conversion of phospho- and galactolipids. Oxylipins can vary greatly in their size, degree of unsaturation, oxidation state, and functional groups. But also isomers with only subtle chemical differences are found. A variety of methods have been developed for separation, detection, and identification of oxylipins. This chapter focuses on the analysis of oxylipins in macroalgae and covers all aspects from sample preparation (including protocols for the investigation of oxylipins in wounded and intact algal tissue), extraction, purification, and subsequent analysis using liquid chromatography coupled to a UV detector or a mass spectrometer. The protocols developed for G. vermiculophylla can be readily adapted to the investigation of other macroalgae.

Evolutionary aspects of lipoxygenases and genetic diversity of human leukotriene signaling

Leukotrienes are pro-inflammatory lipid mediators, which are biosynthesized via the lipoxygenase pathway of the arachidonic acid cascade. Lipoxygenases form a family of lipid peroxidizing enzymes and human lipoxygenase isoforms have been implicated in the pathogenesis of inflammatory, hyperproliferative (cancer) and neurodegenerative diseases. Lipoxygenases are not restricted to humans but also occur in a large number of pro- and eucaryotic organisms. Lipoxygenase-like sequences have been identified in the three domains of life (bacteria, archaea, eucarya) but because of lacking functional data the occurrence of catalytically active lipoxygenases in archaea still remains an open question. Although the physiological and/or pathophysiological functions of various lipoxygenase isoforms have been studied throughout the last three decades there is no unifying concept for the biological importance of these enzymes. In this review we are summarizing the current knowledge on the distribution of lipoxygenases in living single and multicellular organisms with particular emphasis to higher vertebrates and will also focus on the genetic diversity of enzymes and receptors involved in human leukotriene signaling.

Comparative analysis of antiviral responses in Brachypodium distachyon and Setaria viridis reveals conserved and unique outcomes among C3 and C4 plant defenses

Viral diseases cause significant losses in global agricultural production, yet little is known about grass antiviral defense mechanisms. We previously reported on host immune responses triggered by Panicum mosaic virus (PMV) and its satellite virus (SPMV) in the model C3 grass Brachypodium distachyon. To aid comparative analyses of C3 and C4 grass antiviral defenses, here, we establish B. distachyon and Setaria viridis (a C4 grass) as compatible hosts for seven grass-infecting viruses, including PMV and SPMV, Brome mosaic virus, Barley stripe mosaic virus, Maize mild mottle virus, Sorghum yellow banding virus, Wheat streak mosaic virus (WSMV), and Foxtail mosaic virus (FoMV). Etiological and molecular characterization of the fourteen grass-virus pathosystems showed evidence for conserved crosstalk among salicylic acid (SA), jasmonic acid, and ethylene pathways in B. distachyon and S. viridis. Strikingly, expression of PHYTOALEXIN DEFICIENT4, an upstream modulator of SA signaling, was consistently suppressed during most virus infections in B. distachyon and S. viridis. Hierarchical clustering analyses further identified unique antiviral responses triggered by two morphologically similar viruses, FoMV and WSMV, and uncovered other host-dependent effects. Together, the results of this study establish B. distachyon and S. viridis as models for the analysis of plant-virus interactions and provide the first framework for conserved and unique features of C3 and C4 grass antiviral defenses.

Oxylipins from the microalgae Chlamydomonas debaryana and Nannochloropsis gaditana and their activity as TNF-α inhibitors

The chemical study of the microalgae Chlamydomonas debaryana and Nannochloropsis gaditana has led to the isolation of oxylipins. The samples of C. debaryana have yielded the compounds (4Z,7Z,9E,11S,13Z)-11-hydroxyhexadeca-4,7,9,13-tetraenoic acid (1), (4Z,7E,9E,13Z)-11-hydroxyhexadeca-4,7,9,13-tetraenoic acid (2), (4Z,6E,10Z,13Z)-8-hydroxyhexadeca-4,6,10,13-tetraenoic acid (3), (4Z,8E,10Z,13Z)-7-hydroxyhexadeca-4,8,10,13-tetraenoic acid (4), and (5E,7Z,10Z,13Z)-4-hydroxyhexadeca-5,7,10,13-tetraenoic acid (5), which are derived from the fatty acid 16:4Δ(4,7,10,13) together with the compound (5Z,9Z,11E,15Z)-13-hydroxyoctadeca-5,9,11,15-tetraenoic acid (7) derived from coniferonic acid (18:4Δ(5,9,12,15)). In addition, the known polyunsaturated hydroxy acids 11-HHT (6), (5Z,9Z,11E)-13-hydroxyoctadeca-5,9,11-trienoic acid (8), (13S)-HOTE (9), (9E,11E,15Z)-13-hydroxyoctadeca-9,11,15-trienoic acid (10), 9-HOTE (11), 12-HOTE (12), 16-HOTE (13) and (13S)-HODE (14) have also been obtained. The chemical study of N. gaditana has led to the isolation of the hydroxy acid (15S)-HEPE (15) derived from EPA (20:5Δ(5,8,11,14,17)). The structures of the isolated compounds were established by spectroscopic means. The optical activity displayed by oxylipins 1, 2, 6, 7, 9, 10, 14, and 15 suggests the occurrence of LOX-mediated pathways in C. debaryana and N. gaditana. In anti-inflammatory assays, all the tested compounds inhibited the TNF-α production in LPS-stimulated THP-1 macrophages. The most active oxylipin was the C-16 hydroxy acid 1, which at 25μM caused a 60% decrease of the TNF-α level.

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.

Cloning and expression of three lipoxygenase genes from liverwort, Marchantia polymorpha L., in Escherichia coli

Three genes homologous to plant lipoxygenase genes were identified from the EST libraries of Marchantia polymorpha, in order to clarify the function of LOXs in bryophytes. Full-length genes were isolated using 5'- and 3'-RACE methods and named MpLOX1, MpLOX2, and MpLOX3, respectively. To investigate the enzymatic activities of liverwort LOXs, recombinant MpLOX1, MpLOX2, and MpLOX3 proteins were prepared from Escherichia coli cells expressing the corresponding gene. LC-MS/MS analyses and chiral column chromatography of their reaction products showed that MpLOX1 codes for 11S/15S-lipoxygenase against eicosapentaenoic acid and for 15S-lipoxygenase against arachidonic acid, and that MpLOX2 and MpLOX3 code for 15S-lipoxygenase against eicosapentaenoic and arachidonic acids. Phylogenetic analysis showed that the liverwort lipoxygenase genes separated from the ancestor of higher plants in the early stages of plant evolution. Quantification analyses suggested that arachidonic acid and eicosapentaenoic acid were preferred substrates. Furthermore, each liverwort lipoxygenase exhibited highest activity at pH 7.0 and dependency on Ca(2+) ion in the oxygenation reaction.

Evolution of jasmonate and salicylate signal crosstalk

The evolution of land plants approximately 470 million years ago created a new adaptive zone for natural enemies (attackers) of plants. In response to attack, plants evolved highly effective, inducible defense systems. Two plant hormones modulating inducible defenses are salicylic acid (SA) and jasmonic acid (JA). Current thinking is that SA induces resistance against biotrophic pathogens and some phloem feeding insects and JA induces resistance against necrotrophic pathogens, some phloem feeding insects and chewing herbivores. Signaling crosstalk between SA and JA commonly manifests as a reciprocal antagonism and may be adaptive, but this remains speculative. We examine evidence for and against adaptive explanations for antagonistic crosstalk, trace its phylogenetic origins and provide a hypothesis-testing framework for future research on the adaptive significance of SA-JA crosstalk.

Asymmetric total synthesis of (+)-danicalipin A

A convergent asymmetric total synthesis of (+)-danicalipin A is accomplished, in which two chlorinated fragments are stereoselectively joined by 1,3-dipolar coupling, leading to the confirmation of the absolute configuration of the natural product.

Survey of volatile oxylipins and their biosynthetic precursors in bryophytes

Oxylipins are metabolites which are derived from the oxidative fragmentation of polyunsaturated fatty acids. These metabolites play central roles in plant hormonal regulation and defense. Here we survey the production of volatile oxylipins in bryophytes and report the production of a high structural variety of C5, C6, C8 and C9 volatiles of mosses. In liverworts and hornworts oxylipin production was not as pronounced as in the 23 screened mosses. A biosynthetic investigation revealed that both, C18 and C20 fatty acids serve as precursors for the volatile oxylipins that are mainly produced after mechanical wounding of the green tissue of mosses.

Free Fatty Acids and Methyl Jasmonate Trigger Defense Reactions in Laminaria digitata

Arachidonic acid, linolenic acid and methyl jasmonate (MeJA) were found to be strong triggers of an oxidative burst in the kelp Laminaria digitata. These findings constitute the first report of an oxidative burst in an algal system induced by free fatty acids. The source of reactive oxygen species can be at least partially inhibited by diphenylene iodonium (DPI). Treatment with arachidonic acid increases the levels of a number of free fatty acids [including myristic (C14:0), linoleic (C18:2), linolenic (C18:3) and eicosapentaeneoic (C20:5) acids] and hydroxylated derivatives [such as 15-hydroxyeicosatetraenoic acid (15-HETE), 13-hydroxyoctadecatrienoic acid (13-HOTE) and 15-hydroxyeicosapentaenoic acid (15-HEPE)]. Similar to a previous report of the function of an alginate oligosaccharide-triggered oxidative burst in the establishment of resistance in L. digitata against infection by its brown algal endophyte Laminariocolax tomentosoides, C20:4- and MeJA-induced oxidative bursts seem to be involved in establishing the same protection in L. digitata. Altogether, this study supports the notion that lipid oxidation signaling plays a key role in defense induction in marine brown algae.

Enantiocontrolled synthesis of polychlorinated hydrocarbon motifs: a nucleophilic multiple chlorination process revisited

Polychlorinated hydrocarbon motifs have been synthesized in enantiomerically pure forms by means of nucleophilic multiple chlorinations of chiral epoxides, which stereospecifically incorporate halogen atoms into oxygenated molecular scaffolds. The present study demonstrates the scope of the N-chlorosuccinimide (NCS)/organophosphine reagent system that forms multiple sp(3)C-Cl bonds in a regularly repeating pattern with proper stereochemical configurations and evaluates its applicability to various epoxides having elaborate structures. It is noteworthy that tetrachlorinated motifs are produced in one step from bisepoxides by using NCS/Ph(3)P. Furthermore, Ph(2)PCl used in combination with NCS has been found to serve as a potentially useful alternative to NCS/Ph(3)P, especially for promoting dichlorination reactions of alkenyl-substituted epoxides.

Physcomitrella patens has lipoxygenases for both eicosanoid and octadecanoid pathways

Mosses have substantial amounts of long chain C20 polyunsaturated fatty acids, such as arachidonic and eicosapentaenoic acid, in addition to the shorter chain C18 alpha-linolenic and linoleic acids, which are typical substrates of lipoxygenases in flowering plants. To identify the fatty acid substrates used by moss lipoxygenases, eight lipoxygenase genes from Physcomitrella patens were heterologously expressed in Escherichia coli, and then analyzed for lipoxygenase activity using linoleic, alpha-linolenic and arachidonic acids as substrates. Among the eight moss lipoxygenases, only seven were found to be enzymatically active in vitro, two of which selectively used arachidonic acid as the substrate, while the other five preferred alpha-linolenic acid. Based on enzyme assays using a Clark-type oxygen electrode, all of the active lipoxygenases had an optimum pH at 7.0, except for one with highest activity at pH 5.0. HPLC analyses indicated that the two arachidonic acid lipoxygenases form (12S)-hydroperoxy eicosatetraenoic acid as the main product, while the other five lipoxygenases produce mainly (13S)-hydroperoxy octadecatrienoic acid from alpha-linolenic acid. These results suggest that mosses may have both C20 and C18 based oxylipin pathways.

Homology modeling of 5-lipoxygenase and hints for better inhibitor design

Lipoxygenases (LOXs) are a group of enzymes involved in the oxygenation of polyunsaturated fatty acids. Among these 5-lipoxygenase (5-LOX) is the key enzyme leading to the formation of pharmacologically important leukotrienes and lipoxins, the mediators of inflammatory and allergic disorders. In view of close functional similarity to mammalian lipoxygenase, potato 5-LOX is used extensively. In this study, the homology modeling technique has been used to construct the structure of potato 5-LOX. The amino acid sequence identity between the target protein and sequence of template protein 1NO3 (soybean LOX-3) searched from NCBI protein BLAST was 63%. Based on the template structure, the protein model was constructed by using the Homology program in InsightII. The protein model was briefly refined by energy minimization steps and validated using Profile-3D, ERRAT and PROCHECK. The results showed that 99.3% of the amino acids were in allowed regions of Ramachandran plot, suggesting that the model is accurate and its stereochemical quality good. Like all LOXs, 5-LOX also has a two-domain structure, the small N-terminal beta-barrel domain and a larger catalytic domain containing a single atom of non-heme iron coordinating with His525, His530, His716 and Ile864. Asn720 is present in the fifth coordination position of iron. The sixth coordination position faces the open cavity occupied here by the ligands which are docked. Our model of the enzyme is further validated by examining the interactions of earlier reported inhibitors and by energy minimization studies which were carried out using molecular mechanics calculations. Four ligands, nordihydroguaiaretic acid (NDGA) having IC(50) of 1.5 microM and analogs of benzyl propargyl ethers having IC(50) values of 760 microM, 45 microM, and no inhibition respectively were selected for our docking and energy minimization studies. Our results correlated well with the experimental data reported earlier, which proved the quality of the model. This model generated can be further used for the design and development of more potent 5-LOX inhibitors.

Enzymatic synthesis of a bicyclobutane fatty acid by a hemoprotein lipoxygenase fusion protein from the cyanobacterium Anabaena PCC 7120

Biological transformations of polyunsaturated fatty acids often lead to chemically unstable products, such as the prostaglandin endoperoxides and leukotriene A(4) epoxide of mammalian biology and the allene epoxides of plants. Here, we report on the enzymatic production of a fatty acid containing a highly strained bicyclic four-carbon ring, a moiety known previously only as a model compound for mechanistic studies in chemistry. Starting from linolenic acid (C18.3omega3), a dual function protein from the cyanobacterium Anabaena PCC 7120 forms 9R-hydroperoxy-C18.3omega3 in a lipoxygenase domain, then a catalase-related domain converts the 9R-hydroperoxide to two unstable allylic epoxides. We isolated and identified the major product as 9R,10R-epoxy-11trans-C18.1 containing a bicyclo[1.1.0]butyl ring on carbons 13-16, and the minor product as 9R,10R-epoxy-11trans,13trans,15cis-C18.omega3, an epoxide of the leukotriene A type. Synthesis of both epoxides can be understood by initial transformation of the hydroperoxide to an epoxy allylic carbocation. Rearrangement to an intermediate bicyclobutonium ion followed by deprotonation gives the bicyclobutane fatty acid. This enzymatic reaction has no parallel in aqueous or organic solvent, where ring-opened cyclopropanes, cyclobutanes, and homoallyl products are formed. Given the capability shown here for enzymatic formation of the highly strained and unstable bicyclobutane, our findings suggest that other transformations involving carbocation rearrangement, in both chemistry and biology, should be examined for the production of the high energy bicyclobutanes.

Lipid and Fatty Acid Composition of Diatoms Revisited: Rapid Wound-Activated Change of Food Quality Parameters Influences Herbivorous Copepod Reproductive Success

Lipid and fatty acid composition are considered to be key parameters that determine the nutritive quality of phytoplankton diets for zooplanktonic herbivores. The fitness, reproduction and physiology of the grazers are influenced by these factors. The trophic transfer of lipids and fatty acids from algal cells has been typically studied by using simple extraction and quantification approaches, which, as we argue here, do not reflect the actual situation in the plankton. We show that cell disruption, as it occurs during a predator's grazing on diatoms can drastically change the lipid and fatty acid content of the food. In some algae, a rapid depletion of polyunsaturated fatty acids (PUFAs) is observed within the first minutes after cell disruption. This fatty acid depletion is directly linked to the production of PUFA-derived polyunsaturated aldehydes (PUA); these are molecules that are thought to be involved in the chemical defence of the algae. PUA-releasing diatoms are even capable of transforming lipids from other sources if these are available in the vicinity of the wounded cells. Fluorescent staining reveals that the enzymes involved in lipid transformation are active in the foregut of copepods, and therefore link the depletion processes directly to food uptake. Incubation experiments with the calanoid copepod Temora longicornis showed that PUFA depletion in PUA-producing diatoms is correlated to reduced hatching success, and can be compensated for by externally added single fatty acids.

Biosynthesis of Polyunsaturated Short Chain Aldehydes in the DiatomThalassiosira rotula

The diatom Thalassiosira rotula releases polyunsaturated short chain aldehydes (PUA) such as 2E,4Z,7-octatrienal (7a) and 2E,4Z,7Z-decatrienal (3a) upon wounding. Using labeling experiments and synthetic standards, we demonstrate that the mechanism of fatty acid transformation does not follow established lipoxygenase/hydroperoxide lyase pathways known from higher plants or mammals but rather relies on a unique transformation of polyunsaturated hydroperoxy fatty acids. These intermediates are transformed to PUA and short chain hydroxylated fatty acids, which are novel oxylipins. [reaction: see text]

Phospholipases and Galactolipases Trigger Oxylipin-Mediated Wound-Activated Defence in the Red Alga Gracilaria chilensis against Epiphytes

We investigated the wound response of the commercially important red alga, Gracilaria chilensis, in order to obtain insight into its interaction with epiphytic pests. After wounding, the host releases free fatty acids as well as the hydroxylated eicosanoids, 8R-hydroxy eicosatetraenoic acid (8-HETE) and 7S,8R-dihydroxy eicosatetraenoic acid (7,8-di-HETE). While the release of free arachidonic acid and subsequent formation of 8-HETE is controlled by phospholipase A, 7,8-di-HETE production is independent of this lipase. This dihydroxylated fatty acid might be directly released from galactolipids. Physiologically relevant concentrations of oxylipins reduced spore settlement of Acrochaetium sp. (Rhodophyta, Acrochaetiaceae) and suppressed the development of hapteria in Ceramium rubrum (Rhodophyta, Ceramiaceae) when these model epiphytes were exposed to artificial surfaces that contained 8-HETE or 7,8-di-HETE. Thus, the immediate release of oxylipins can be seen as G. chilensis defence against epiphytes.

Lipids and lipid metabolism in eukaryotic algae

Eukaryotic algae are a very diverse group of organisms which inhabit a huge range of ecosystems from the Antarctic to deserts. They account for over half the primary productivity at the base of the food chain. In recent years studies on the lipid biochemistry of algae has shifted from experiments with a few model organisms to encompass a much larger number of, often unusual, algae. This has led to the discovery of new compounds, including major membrane components, as well as the elucidation of lipid signalling pathways. A major drive in recent research have been attempts to discover genes that code for expression of the various proteins involved in the production of very long-chain polyunsaturated fatty acids such as arachidonic, eicosapentaenoic and docosahexaenoic acids. Such work is described here together with information about how environmental factors, such as light, temperature or minerals, can change algal lipid metabolism and how adaptation may take place.

Diatom/copepod interactions in plankton: the indirect chemical defense of unicellular algae

Numerous coexisting species can be observed in the open oceans. This includes the complex community of the plankton, which comprises all free floating organisms in the sea. Traditionally, nutrient limitation, competition, predation, and abiotic factors have been assumed to shape the community structure in this environment. Only in recent years has the idea arisen that chemical signals and chemical defense can influence species interactions in the plankton as well. Key players at the base of the marine food web are diatoms (unicellular algae with silicified cell walls) and their main predators, the herbivorous copepods. It was assumed that diatoms represent a generally good food source for the grazers but recent work indicates that some species use chemical defenses. Secondary metabolites, released by these algae immediately after wounding, are targeted not against the predators themselves but rather at interfering with their reproductive success. This strategy allows diatoms to reduce the grazer population, thereby influencing the marine food web. This review addresses the chemical ecology of the defensive oxylipins formed by diatoms and the question of how these metabolites can act in such a dilute environment. Aspects of biosynthesis, bioassays, and the possible implications of such a chemical defense for the plankton community structure are also discussed.

A multifunctional lipoxygenase with fatty acid hydroperoxide cleaving activity from the moss Physcomitrella patens

A complex mixture of fatty acid-derived aldehydes, ketones, and alcohols is released upon wounding of the moss Physcomitrella patens. To investigate the formation of these oxylipins at the molecular level we isolated a lipoxygenase from P. patens, which was identified in an EST library by sequence homology to lipoxygenases from plants. Sequence analysis of the cDNA showed that it exhibits a domain structure similar to that of type2 lipoxygenases from plants, harboring an N-terminal import signal for chloroplasts. The recombinant protein was identified as arachidonate 12-lipoxygenase and linoleate 13-lipoxygenase with a preference for arachidonic acid and eicosapentaenoic acid. In contrast to any other lipoxygenase cloned so far, this enzyme exhibited in addition an unusual high hydroperoxidase and also a fatty acid chain-cleaving lyase activity. Because of these unique features the pronounced formation of (2Z)-octen-1-ol, 1-octen-3-ol, the dienal (5Z,8Z,10E)-12-oxo-dodecatrienoic acid and 12-keto eicosatetraenoic acid was observed when arachidonic acid was administered as substrate. 12-Hydroperoxy eicosatetraenoic acid was found to be only a minor product. Moreover, the P. patens LOX has a relaxed substrate tolerance accepting C(18)-C(22) fatty acids giving rise to even more LOX-derived products. In contrast to other lipoxygenases a highly diverse product spectrum is formed by a single enzyme accounting for most of the observed oxylipins produced by the moss. This single enzyme might, in a fast and effective way, be involved in the formation of signal and/or defense molecules thus contributing to the broad resistance of mosses against pathogens.

A single active site residue directs oxygenation stereospecificity in lipoxygenases: stereocontrol is linked to the position of oxygenation

Lipoxygenases are a class of dioxygenases that form hydroperoxy fatty acids with distinct positional and stereo configurations. Several amino acid residues influencing regiospecificity have been identified, whereas the basis of stereocontrol is not understood. We have now identified a single residue in the lipoxygenase catalytic domain that is important for stereocontrol; it is conserved as an Ala in S lipoxygenases and a Gly in R lipoxygenases. Our results with mutation of the conserved Ala to Gly in two S lipoxygenases (mouse 8S-LOX and human 15-LOX-2) and the corresponding Gly-Ala substitution in two R lipoxygenases (human 12R-LOX and coral 8R-LOX) reveal that the basis for R or S stereo-control also involves a switch in the position of oxygenation on the substrate. After the initial hydrogen abstraction, antarafacial oxygenation at one end or the other of the activated pair of double bonds (pentadiene) gives, for example, 8S or 12R product. The Ala residue promotes oxygenation on the reactive pentadiene at the end deep in the substrate binding pocket and S stereochemistry of the product hydroperoxide, and a Gly residue promotes oxygenation at the proximal end of the reactive pentadiene resulting in R stereochemistry. A model of lipoxygenase reaction specificity is proposed in which product regiochemistry and stereochemistry are determined by fixed relationships between substrate orientation, hydrogen abstraction, and the Gly or Ala residue we have identified.

Intracellular Compartmentation in the Biosynthesis of Caulerpenyne: Study on Intact Macroalgae Using Stable-Isotope-Labeled Precursors

The biosynthesis of caulerpenyne 1 was studied in the invasive green alga Caulerpa taxifolia. The investigation was performed on intact algae with stable-isotope-labeled precursors administered under mixotrophic growth conditions. According to the labeling pattern, after incorporation of 1-(13)C-acetate and (13)CO(2), respectively, the biosynthesis of the sesquiterpene backbone occurs in the chloroplast and follows the methyl-erythritol-4-phosphate (MEP) pathway. In contrast, the acetyl residues of caulerpenyne 1 are derived from a cytosolic resource. [structure: see text]

Hydroperoxy-arachidonic acid mediated n-hexanal and (Z)-3- and (E)-2-nonenal formation in Laminaria angustata

In higher plants, C6 and C9 aldehydes are formed from C18 fatty acids, such as linoleic or linolenic acid, through formation of 13- and 9-hydroperoxides, followed by their stereospecific cleavage by fatty acid hydroperoxide lyases (HPL). Some marine algae can also form C6 and C9 aldehydes, but their precise biosynthetic pathway has not been elucidated fully. In this study, we show that Laminaria angustata, a brown alga, formed C6 and C9 aldehydes enzymatically. The alga forms C9 aldehydes exclusively from the C20 fatty acid, arachidonic acid, while C6 aldehydes are derived either from C18 or from C20 fatty acid. The intermediates in the biosynthetic pathway were trapped by using a glutathione/glutathione peroxidase system, and subjected to structural analyses. Formation of (S)-12-, and (S)-15-hydroperoxy arachidonic acids [12(S)HPETE and 15(S)HPETE] from arachidonic acid was confirmed by chiral HPLC analyses. These account respectively for C9 aldehyde and C6 aldehyde formation, respectively. The HPL that catalyzes formation of C9 aldehydes from 12(S)HPETE seems highly specific for hydroperoxides of C20 fatty acids.

Comparison of growth and lipid composition in the green abalone, Haliotis fulgens, provided specific macroalgal diets

Lipid composition of abalone was examined over a one-year interval. A feeding trial was designed to cover a full reproductive cycle in young adult green abalone, Haliotis fulgens, consisting of five diet treatments: the macrophytic algal phaeophyte Egregia menziesii, rhodophyte Chondracanthus canaliculatus, chlorophyte Ulva lobata, a composite of the three algae and a starvation control. The lipid class, fatty acid, sterol and 1-O-alkyl glyceryl ether profiles were determined for foot, hepatopancreas/gonad tissues and larvae. The major fatty acids were 16:0, 18:0, 18:1(n-7)c, 18:1(n-9)c, 20:4(n-6), 20:5(n-3) and 22:5(n-3), as well as 14:0 for abalone fed brown and red algae. 4,8,12-Trimethyltridecanoic acid, derived from algae, was detected for the first time in H. fulgens (hepatopancreas complex, 1.2-13.9%; larvae, 0.5% of total fatty acids). Diacylglyceryl ethers were present in larvae (0.6% of total lipid). The major 1-O-alkyl glycerols were 16:0, 16:1 and 18:0. Additionally, 18:1(n-9) was a major component in hepatopancreas/gonad and larvae. The major sterol was cholesterol (96-100% of total sterols). Highest growth rates were linked to temperature and occurred in abalone fed the phaeophyte E. menziesii (43 microm.day(-1), 56 mg.day(-1) yearly mean), an alga containing the highest levels of C(20) polyunsaturated fatty acids and the highest ratio of 20:4(n-6) to 20:5(n-3). This study provides evidence of the influence of diet and temperature on seasonal changes in abalone lipid profiles, where diet is most strongly related to body mass and temperature to shell length. The allocation of lipids to specific tissues in green abalone clarifies their lipid metabolism. These results provide a basis for improving nutrition of abalone in mariculture through formulation of artificial feeds.

5-Lipoxygenase-derived oxylipins from the red alga Rhodymenia pertusa

The lipid extract of the temperate red alga Rhodymenia pertusa has yielded four eicosanoid metabolites, three of which are new natural products. Using principally NMR and MS techniques, their structures were deduced as 5R,6S-dihydroxy-7(E),9(E),11(Z),14(Z)-eicosatetraenoic acid (5R,6S-diHETE), 5R*,6S*-dihydroxy-7(E),9(E),11(Z),14(Z),17(Z)-eicosapentaenoic acid (5R*,6S*-diHEPE), 5-hydroxy-6(E),8(Z),11(Z),14(Z)-eicosatetraenoic acid (5-HETE), 5-hydroxy-6(E),8(Z),11(Z),14(Z),17(Z)-eicosapentaenoic acid (5-HEPE). The co-occurrence of these metabolites strongly suggests that R. pertusa contains a unique 5R-lipoxygenase system acting on both arachidonic and eicosapentaenoic acids.