Isolation and characterization of a soybean (Glycine max) lipoxygenase-3 gene

Recombinant Soybean Lipoxygenase 2 (GmLOX2) Acts Primarily as a ω6(S)-Lipoxygenase

The lipoxygenase (LOX) cascade is a source of bioactive oxylipins that play a regulatory role in plants, animals, and fungi. Soybean (Glycine max (L.) Merr.) LOXs are the classical models for LOX research. Progress in genomics has uncovered a large diversity of GmLOX isoenzymes. Most of them await biochemical investigations. The catalytic properties of recombinant soybean LOX2 (GmLOX2) are described in the present work. The GmLOX2 gene has been cloned before, but only for nucleotide sequencing, while the recombinant protein was not prepared and studied. In the present work, the recombinant GmLOX2 behavior towards linoleic, α-linolenic, eicosatetraenoic (20:4), eicosapentaenoic (20:5), and hexadecatrienoic (16:3) acids was examined. Linoleic acid was a preferred substrate. Oxidation of linoleic acid afforded 94% optically pure (13S)-hydroperoxide and 6% racemic 9-hydroperoxide. GmLOX2 was less active on other substrates but possessed an even higher degree of regio- and stereospecificity. For example, it converted α-linolenic acid into (13S)-hydroperoxide at about 98% yield. GmLOX2 showed similar specificity towards other substrates, producing (15S)-hydroperoxides (with 20:4 and 20:5) or (11S)-hydroperoxide (with 16:3). Thus, the obtained data demonstrate that soybean GmLOX2 is a specific (13S)-LOX. Overall, the catalytic properties of GmLOX2 are quite similar to those of GmLOX1, but pH is optimum.

TILLING by sequencing to identify induced mutations in stress resistance genes of peanut (Arachis hypogaea)

Background

Targeting Induced Local Lesions in Genomes (TILLING) is a powerful reverse genetics approach for functional genomics studies. We used high-throughput sequencing, combined with a two-dimensional pooling strategy, with either minimum read percentage with non-reference nucleotide or minimum variance multiplier as mutation prediction parameters, to detect genes related to abiotic and biotic stress resistances. In peanut, lipoxygenase genes were reported to be highly induced in mature seeds infected with Aspergillus spp., indicating their importance in plant-fungus interactions. Recent studies showed that phospholipase D (PLD) expression was elevated more quickly in drought sensitive lines than in drought tolerant lines of peanut. A newly discovered lipoxygenase (LOX) gene in peanut, along with two peanut PLD genes from previous publications were selected for TILLING. Additionally, two major allergen genes Ara h 1 and Ara h 2, and fatty acid desaturase AhFAD2, a gene which controls the ratio of oleic to linoleic acid in the seed, were also used in our study. The objectives of this research were to develop a suitable TILLING by sequencing method for this allotetraploid, and use this method to identify mutations induced in stress related genes.

Results

We screened a peanut root cDNA library and identified three candidate LOX genes. The gene AhLOX7 was selected for TILLING due to its high expression in seeds and roots. By screening 768 M2 lines from the TILLING population, four missense mutations were identified for AhLOX7, three missense mutations were identified for AhPLD, one missense and two silent mutations were identified for Ara h 1.01, three silent and five missense mutations were identified for Ara h 1.02, one missense mutation was identified for AhFAD2B, and one silent mutation was identified for Ara h 2.02. The overall mutation frequency was 1 SNP/1,066 kb. The SNP detection frequency for single copy genes was 1 SNP/344 kb and 1 SNP/3,028 kb for multiple copy genes.

Conclusions

Our TILLING by sequencing approach is efficient to identify mutations in single and multi-copy genes. The mutations identified in our study can be used to further study gene function and have potential usefulness in breeding programs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1348-0) contains supplementary material, which is available to authorized users.

Differential response to sulfur nutrition of two common bean genotypes differing in storage protein composition

It has been hypothesized that the relatively low concentration of sulfur amino acids in legume seeds might be an ecological adaptation to nutrient poor, marginal soils. SARC1 and SMARC1N-PN1 are genetically related lines of common bean (dry bean, Phaseolus vulgaris) differing in seed storage protein composition. In SMARC1N-PN1, the lack of phaseolin and major lectins is compensated by increased levels of sulfur-rich proteins, resulting in an enhanced concentration of cysteine and methionine, mostly at the expense of the abundant non-protein amino acid, S-methylcysteine. To identify potential effects associated with an increased concentration of sulfur amino acids in the protein pool, the response of the two genotypes to low and high sulfur nutrition was evaluated under controlled conditions. Seed yield was increased by the high sulfate treatment in SMARC1N-PN1. The seed concentrations of sulfur, sulfate, and S-methylcysteine were altered by the sulfur treatment in both genotypes. The concentration of total cysteine and extractible globulins was increased specifically in SMARC1N-PN1. Proteomic analysis identified arcelin-like protein 4, lipoxygenase-3, albumin-2, and alpha amylase inhibitor beta chain as having increased levels under high sulfur conditions. Lipoxygenase-3 accumulation was sensitive to sulfur nutrition only in SMARC1N-PN1. Under field conditions, both SARC1 and SMARC1N-PN1 exhibited a slight increase in yield in response to sulfur treatment, typical for common bean.

Selection and molecular characterization of a lipoxygenase-free soybean mutant line induced by gamma irradiation

KEY MESSAGE

A lipoxygenase-free soybean mutant line (H70) induced by gamma ray was selected and its detailed information about the lipoxygenase was analyzed by comparison of DNA sequence. Soybean seeds contain three lipoxygenase enzymes, which induce a beany or grassy flavor. The elimination of lipoxygenases can reduce the poor stability and off-flavors of soybean oil and protein products. In this study, we selected a soybean mutant (H70) in which the three lipoxygenases had been mutated using gamma rays. To obtain detailed information about the lipoxygenase, we investigated the sequences of the Lox1, Lox2 and Lox3 genes in H70 compared to the original cultivar, Hwanggum. Comparisons of the sequences of the Lox1 and Lox2 genes in H70 with those in a line with normal lipoxygenase (HG) showed that the mutations in these genes affected a highly conserved group of six histidine residues necessary for enzymatic activity. Lox1 in H70 contained a 74 bp deletion in exon 8, creating a stop codon that prematurely terminates translation. A single point mutation (T-A) in exon 8 of Lox2 changed histidine (H532, one of the iron-binding ligands essential for Lox2 activity) to glutamine. The mutation in the Lox3 gene in H70 was a single-point mutation in exon 6 (A-G), which changed the amino acid from histidine to arginine. This amino acid alteration in Lox3 was located in the N-terminal barrel, which might play a role in molecular recognition during catalysis and/or proteolysis. These results suggest that gene analysis based on DNA sequencing could be useful for elucidating the lipoxygenase content in soybean mutant lines. Additionally, the soybean mutant line selected in this study could be used to develop soybean cultivars with improved flavor.

A trichome-specific linoleate lipoxygenase expressed during pyrethrin biosynthesis in pyrethrum

The lipid precursor alcohols of pyrethrins-jasmolone, pyrethrolone and cinerolone-have been proposed as sharing parts of the oxylipin pathway with jasmonic acid. This implies that one of the first committed steps of pyrethrin biosynthesis is catalyzed by a lipoxygenase, catalyzing the hydroperoxidation of linolenic acid at position 13. Previously, we showed that the expression and activity of chrysanthemyl diphosphate synthase (TcCDS), the enzyme catalyzing the first committed step in the biosynthesis of the acid moiety of pyrethrins, is trichome-specific and developmentally regulated in flowers. In the present study we characterized the expression pattern of 25 lipoxygenase EST contigs, and subsequently carried out the molecular cloning of two pyrethrum lipoxygenases, TcLOX1 and TcLOX2, that have a similar pattern to TcCDS. Only recombinant TcLOX1 catalyzed the peroxidation of the linolenic acid substrate. Just as TcCDS, TcLOX1, are exclusively expressed in trichomes. Phylogenetic analysis showed that the enzyme shared the highest homology with chloroplast-localized 13-type-lipoxygenases that are involved in maintaining basal levels of jasmonate.

Molecular basis of seed lipoxygenase null traits in soybean line OX948

The poor stability and off-flavors of soybean oil and protein products can be reduced by eliminating lipoxygenases from soybean seed. Mature seeds of OX948, a lipoxygenase triple null mutant line, do not contain lipoxygenase proteins. The objective of this study was to determine the molecular basis of the seed lipoxygenase null traits in OX948. Comparisons of the sequences for lipoxygenase 1 (Lx1) and lipoxygenase 2 (Lx2) genes in the mutant (OX948) with those in a line with normal lipoxygenase levels (RG10) showed that the mutations in these genes affected a highly conserved group of six histidines necessary for enzymatic activity. The OX948 mutation in Lx1 is a 74 bp deletion in exon 8, which introduces a stop codon that prematurely terminates translation. A single T-A substitution in Lx2 changes histidine H532 (one of the iron-binding ligands essential for L-2 activity) to glutamine. The mutation in the lipoxygenase 3 (Lx3) gene in OX948 is in the promoter region and represents two single base substitutions in a cis-acting AAATAC paired box. All three mutations would result in the loss of lipoxygenase activity in mature seed. The seed lipoxygenase gene mutation-based molecular markers could be used to accelerate and simplify breeding efforts for soybean cultivars with improved flavor.

Overexpression of hydroperoxide lyase gene in Nicotiana benthamiana using a viral vector system

13-Lipoxygenase (13-LOX) and 13-hydroperoxide lyases (13-HPL) are the key enzymes for the production of the 'green note' compounds hexanal, (3Z)- and (2E)-hexenal in plant tissues. To produce high levels of 13-LOX and 13-HPL enzymatic activities for a biocatalytic process to generate C(6)-aldehydes on a large scale, soya bean 13-LOX (GmVLXC) and watermelon 13-HPL (ClHPL) genes were expressed in Nicotiana benthamiana using a viral vector system mediated by agroinfiltration. The N. benthamiana leaves produced high activity of watermelon HPL, but not GmVLXC 13-LOX. In addition, all leaves treated with bacterial suspension displayed a high activity of 9-LOX, indicating that the internal tobacco 9-LOX gene was highly induced through agroinfiltration because of wounding. GmVLXC and ClHPL transcripts could be detected in the corresponding transformed tobacco leaves by real-time RT-PCR analysis but the expression level of ClHPL was 24-fold higher than that of GmVLXC. Western blot analysis showed that LOX was present in all tobacco leaves which were treated with bacterial suspensions, but not in the untreated wild-type control. This result confirms that internal 9-LOX was highly induced by agroinfiltration. The highest levels of ClHPL activity under optimal infiltration conditions were 80 times the HPL activity of wild-type plants or plants transformed with control vector. A large amount of hexanal was formed when linoleic acid was incubated with extracts from N. benthamiana leaves over-expressing ClHPL in combination with GmVLXC-expressing yeast extracts. One gram of ClHPL-expressing N. benthamiana leaves (fresh weight) could produce 17 +/- 0.4 mg hexanal from 50 mg linoleic acid after 30 min.

Proteomic identification and characterization of a novel peroxisomal adenine nucleotide transporter supplying ATP for fatty acid beta-oxidation in soybean and Arabidopsis

We have identified the novel protein Glycine max PEROXISOMAL ADENINE NUCLEOTIDE CARRIER (Gm PNC1) by proteomic analyses of peroxisomal membrane proteins using a blue native/SDS-PAGE technique combined with peptide mass fingerprinting. Gm PNC1, and the Arabidopsis thaliana orthologs At PNC1 and At PNC2, were targeted to peroxisomes. Functional integration of Gm PNC1 and At PNC2 into the cytoplasmic membranes of intact Escherichia coli cells revealed ATP and ADP import activities. The amount of Gm PNC1 in cotyledons increased until 5 d after germination under constant darkness and then decreased very rapidly in response to illumination. We investigated the physiological functions of PNC1 in peroxisomal metabolism by analyzing a transgenic Arabidopsis plant in which At PNC1 and At PNC2 expression was suppressed using RNA interference. The pnc1/2i mutant required sucrose for germination and suppressed the degradation of storage lipids during postgerminative growth. These results suggest that PNC1 contributes to the transport of adenine nucleotides that are consumed by reactions that generate acyl-CoA for peroxisomal fatty acid beta-oxidation during postgerminative growth.

A novel lipoxygenase gene from developing rice seeds confers dual position specificity and responds to wounding and insect attack

OsLOX1 is a novel full-length cDNA isolated from developing rice seeds. We have examined its biochemical properties and expression patterns. The protein has dual positional specificity, as it releases both C-9 and C-13 oxidized products in a 4:3 ratio. OsLOX1 transcripts were detected at low abundance in immature seeds and newly germinated seedlings, but accumulate rapidly and transiently in response to wounding or brown planthopper (BPH) attack, reaching a peak 3 h after wounding and 6 h after insect feeding. We produced transgenic rice lines carrying either sense or antisense constructs under the control of a cauliflower mosaic virus 35S promoter, and these rice lines showed altered OsLOX1 activity. In all of the antisense lines and more than half of the sense lines the expression levels of OsLOX1, the levels of enzyme activity, and the levels of the endogenous OsLOX1 products (jasmonic acid, (Z)-3-hexenal and colneleic acid) at 6, 48, and 48 h after BPH feeding respectively, were below the levels found in non-transgenic control plants; yet, the levels in the remaining sense transformants were enhanced relative to controls. Transformants with a lower level of OsLOX1 expression were less able to tolerate BPH attack, while those with enhanced OsLOX1 expression were more resistant. Our data suggest that the OsLOX1 product is involved in tolerance of the rice plant to wounding and BPH attack.

Sensitivity and speed of induced defense of cabbage (Brassica oleracea L.): dynamics of BoLOX expression patterns during insect and pathogen attack

The lipoxygenase pathway is involved in the early steps of plant responses to herbivorous insects and phytopathogens. Induced defenses in the crucifer Brassica oleracea have been well documented. Here, we have cloned a LIPOXYGENASE (LOX) from B. oleracea (BoLOX). The sequence reveals that the BoLOX protein has a transit peptide for chloroplast targeting, which is characteristic for class 2 LOXs involved in jasmonic acid (JA) biosynthesis which takes place in the chloroplast. Phylogenetic analysis shows that BoLOX is closely related to B. napus BnLOX2fl and Arabidopsis thaliana AtLOX2, which mediates JA biosynthesis. BoLOX also shares functional characteristics with AtLOX2; BoLOX is inducible by wounding, JA treatment, and herbivores such as caterpillars (Pieris rapae, P. brassicae, and Mamestra brassicae), spider mites (Tetranychus urticae), locusts (Schistocerca gregaria), and a bacterial pathogen (Pseudomonas syringae pv. tomato). Of these, Pieris spp. caterpillars also induce AtLOX2 and JA biosynthesis in Arabidopsis. However, the aphid Myzus persicae did not induce BoLOX, which agrees with previous reports that this aphid induces neither AtLOX2 nor JA biosynthesis in Arabidopsis. Quantitative expression analysis of temporal, spatial, and density-dependent BoLOX transcript levels through real-time quantitative polymerase chain reaction demonstrated that BoLOX is maximally expressed after feeding by only two first-instar caterpillars for 24 h. Systemic expression was approximately 10-fold lower than local expression for herbivore-induced responses. The good correlation of BoLOX transcript levels with reports in the literature on induced defenses of B. oleracea is discussed.

Molecular properties and activities of tuber proteins from starch potato cv. Kuras

Potato starch production leaves behind a huge amount of juice. This juice is rich in protein, which might be exploited for food, biotechnological, and pharmaceutical applications. In northern Europe cv. Kuras is dominant for industrial starch production, and juice protein of freshly harvested mature tubers was fractionated by Superdex 200 gel filtration. The fractions were subjected to selected activity assays (patatin, peroxidase, glyoxalases I and II, alpha-mannosidase, inhibition of trypsin, Fusarium protease, and alcalase) and protein subunit size determination by SDS-PAGE and mass spectrometry. Proteins present in SDS-PAGE bands were identified by tryptic peptide mass fingerprinting. Protein complexes such as ribosomes and proteasomes eluted with the void volume of the gel filtration. Large proteins were enzymes of starch synthesis dominated by starch phosphorylase L-1 (ca. 4% of total protein). Five identified dimeric patatin variants (25%) coeluted with four monomeric lipoxygenase variants (10%) at 97 kDa. Protease inhibitor I variants (4%) at 46 kDa (hexamer) inhibited alcalase. Fourteen Kunitz protease inhibitor variants (30%) at 19 kDa inhibited trypsin and Fusarium protease. Carboxypeptidase inhibitor variants (5%) and defensins (5%) coeluted with phenolics. The native sizes and molecular properties were determined for 43 different potato tuber proteins, several for the first time.

Biochemical and molecular characterization of hazelnut (Corylus avellana) seed lipoxygenases

Plant lipoxygenases (LOXs) are a class of dioxygenases which display diverse functions in several physiological processes such as growth, development and response to biotic and abiotic stresses. Even though LOXs have been characterized from several plant species, the physiological role of seed LOXs is still unclear. With the aim to better clarify the occurrence of LOXs and their influence on hazelnut seed quality, we carried out the biochemical and molecular characterization of the main LOX isoforms expressed during seed development. A genomic clone containing a complete LOX gene was isolated and fully characterized. The 9887 bp sequence reported contains an open reading frame of 5334 bp encoding a putative polypeptide of 99 kDa. Semiquantitative RT-PCR carried out from RNAs extracted from seeds at different maturation stages showed that LOXs are mainly expressed at early developmental stages. These results were confirmed by LOX activity assays. Biochemical characterization of the reaction products of the hazelnut LOX indicated that it is a 9-LOX. Two cDNAs were isolated by RT-PCR carried out on total RNA from immature hazelnut seeds. Sequence analysis indicated that the two cDNAs are highly homologous (91.9% degree of identity) and one of these corresponded exactly to the genomic clone. The deduced amino acid sequences of the hazelnut LOXs showed that they are closely related to a previously reported almond LOX (79.5% identity) and, to a lesser extent, to some LOXs involved in plant responses to pathogens (cotton and tobacco LOXs, 75.5 and 74.6% identity, respectively). The physiological role of hazelnut LOXs and their role in influencing seed quality are also discussed.

Molecular cloning and biochemical characterization of a lipoxygenase in almond (Prunus dulcis) seed

We have characterized an almond (Prunus dulcis) lipoxygenase (LOX) that is expressed early in seed development. The presence of an active lipoxygenase was confirmed by western blot analysis and by measuring the enzymatic activity in microsomal and soluble protein samples purified from almond seeds at this stage of development. The almond lipoxygenase, which had a pH optimum around 6, was identified as a 9-LOX on the basis of the isomers of linoleic acid hydroperoxides produced in the enzymatic reaction. A genomic clone containing a complete lipoxygenase gene was isolated from an almond DNA library. The 6776-bp sequence reported includes an open reading frame of 4667 bp encoding a putative polypeptide of 862 amino acids with a calculated molecular mass of 98.0 kDa and a predicted pI of 5.61. Almond seed lipoxygenase shows 71% identity with an Arabidopsis LOX1 gene and is closely related to tomato fruit and potato tuber lipoxygenases. The sequence of the active site was consistent with the isolated gene encoding a 9-LOX.

Specific lipoxygenase isoforms accumulate in distinct regions of soybean pod walls and mark a unique cell layer

Developing seeds constitute a strong sink for the plant and rely on the turnover and mobilization of carbon and nitrogen assimilates to supply the nutrients needed for their maturation. In large part these nutrients emanate from the vegetative organs including leaves and pod walls. Vegetative lipoxygenases (VLXs) accumulate in the paraveinal mesophyll cell layer of soybean (Glycine max L.) leaves where individual isoforms are proposed to play a role(s) as active enzymes or as transient storage proteins. VLXs also are prominent proteins in soybean pod walls, representing approximately 12% of the total soluble protein. Examining the temporal, tissue, and subcellular patterns of individual VLX isoform accumulation and of lipoxygenase activity through pod wall development indicates that VLXD is the principal VLX isoform playing a role in storage in this organ. The major accumulation of VLXD occurs just prior to seed fill within the endocarp middle zone, and protein extracted from this region shows relatively low levels of lipoxygenase activity, suggesting the middle zone may act as a storage tissue. Three other VLX isoforms, VLXA, VLXB, and VLXC colocalize to the cytoplasm of a single discrete cell layer in the mesocarp. Thus, the patterns of VLX cellular and subcellular localization in pod walls suggest independent functions for these different isoforms while also serving as specific markers for a novel cell layer in the pod wall.

Protein dynamics, activity and cellular localization of soybean lipoxygenases indicate distinct functional roles for individual isoforms

Vegetative lipoxygenases (VLXs) in soybean are hypothesized to function in nitrogen storage and partitioning. Isoform-specific antibodies for four of the five known VLX isoenzymes were used to investigate the influence of source-sink status on protein levels, as well as to analyze the tissue and subcellular localization of the different isoforms. VLXD responded most strongly to sink limitation, although the levels of VLXA, B and C increased as well. After sink limitation, VLXD and the vegetative storage protein, VSPalpha, accumulated in the vacuoles of bundle sheath and paraveinal mesophyll cells, while VLXA, B and C localized to the cytosol of these cells. All five known VLX isoenzymes were active with both linoleic and linolenic acid substrates after expression in Escherichia coli. The strong upregulation of VLXD levels after sink limitation as well as the localization of this isoform to the vacuoles of paraveinal mesophyll and bundle sheath cells (where VSPs are found) strongly suggest that VLXD should be considered as a major storage protein in soybean leaves. Furthermore, since VLXA, B and C also accumulate in sink-limited soybean leaves, are located in the cytosol of paraveinal mesophyll cells and are active at pH values typically found in this compartment, their activities may well contribute to lipid metabolism in this tissue. This multi-gene family is thus ideally poised to play a pivotal role in the balance of N deposition relative to lipid-based storage, defense or signaling, by modulating contributions to these processes in the transient storage cells of the paraveinal mesophyll.

Purification and characterization of a lipoxygenase enzyme from durum wheat semolina

Purification of a lipoxygenase enzyme from the cultivar Tresor of durum wheat semolina (Triticum turgidum var. durum Desf) was reinvestigated furnishing a new procedure. The 895-fold purified homogeneous enzyme showed a monomeric structure with a molecular mass of 95 +/- 5 kDa. Among the substrates tested, linoleic acid showed the highest k(cat)/K(m) value; a beta-carotene bleaching activity was also detected. The enzyme optimal activity was at pH 6. 8 on linoleic acid as substrate and at pH 5.2 for the bleaching activity on beta-carotene, both assayed at 25 degrees C. The dependence of lipoxygenase activity on temperature showed a maximum at 40 degrees C for linoleic acid and at 60 degrees C for bleaching activity on beta-carotene. The amino acid composition showed the presence of only one tryptophan residue per monomer. Far-UV circular dichroism studies carried out at 25 degrees C in acidic, neutral, and basic regions revealed that the protein possesses a secondary structure content with a high percentage of alpha- and beta-structures. Near-UV circular dichroism, at 25 degrees C and at the same pH values, pointed out a strong perturbation of the tertiary structure in the acidic and basic regions compared to the neutral pH condition. Moreover, far-UV CD spectra studying the effects of the temperature on alpha-helix content revealed that the melting point of the alpha-helix is at 60 degrees C at pH 5.0, whereas it was at 50 degrees C at pH 6.8 and 9.0. The NH(2)-terminal sequence allowed a homology comparison with other lipoxygenase sequences from mammalian and vegetable sources.

Physiological correlation between glycyrrhizin, glycyrrhizin-binding lipoxygenase and casein kinase II

By means of glycyrrhizin (GL)-affinity column chromatography, a GL-binding lipoxygenase (gbLOX) was selectively purified from the partially purified soybean LOX-1 fraction. Polypeptide analysis of the purified gbLOX by SDS-PAGE detected two distinct polypeptides (p96 and p94), which were identical to LOX-3 as determined by their partial N-terminal amino acid sequences. Moreover, it was found that (i) phosphorylation of gpLOX by casein kinase II (CK-II) is significantly stimulated by 3 microM GL, but inhibited by 30 microM GL or 10 microM oGA; and (ii) gbLOX activity is enhanced when the enzyme is phosphorylated by CK-II in the presence of 3 microM GL. These results suggest that (i) CK-II is a kinase responsible for the activation of gbLOX through its specific phosphorylation; and (ii) GL is one of the regulatory substances for specific phosphorylation of gbLOX (LOX-3) by CK-II in plant cells.

DIOXYGENASES: Molecular Structure and Role in Plant Metabolism

▪ Abstract  Dioxygenases are nonheme iron-containing enzymes important in the biosynthesis of plant signaling compounds such as abscisic acid, gibberellins, and ethylene and also of secondary metabolites, notably flavonoids and alkaloids. Plant dioxygenases fall into two classes: lipoxygenases and 2-oxoacid-dependent dioxygenases. The latter catalyze hydroxylation, epoxidation, and desaturation reactions; some enzymes catalyze more than one type of reaction in successive steps in a biosynthetic pathway. This review highlights recent discoveries on both enzyme groups, particularly in relation to gibberellin biosynthesis, in vivo activity of 1-aminocyclopropane-1-carboxylate oxidase, and molecular structure/function relationships. Similarities between the roles of monooxygenases and dioxygenases are also discussed.

Uses of biotechnology in modifying plant lipids

This review discusses fatty acid modification of oilseeds with additional emphasis on production of oxygenated derivatives. In a relatively short period, less than a decade, our understanding of the enzymes involved in plant fatty acid synthesis has increased to the point where we understand how they might be used in oilseed modification. Further, through modern molecular biological techniques, the actual genes for many of these important enzymes have been cloned. Use of genetic transformation systems has allowed us to fundamentally alter the normal biosynthetic pathways in highly specific ways, in manners that would be either difficult or impossible using traditional breeding techniques. Alteration of plant lipid biosynthesis is not restricted to using genes from the plants themselves, but interspecies transfer is possible, either from completely unrelated plant species (often of no commercial value but possessing unusual biochemical properties) or from animals, fungi, and prokaryotic organisms. In this way "designer" plants possessing altered metabolism, tailored to the interests or needs of certain industries, nutritionists, and the consumer can be created.

Structure conservation in lipoxygenases: structural analysis of soybean lipoxygenase-1 and modeling of human lipoxygenases

Lipoxygenases are a class of non-heme iron dioxygenases which catalyze the hydroperoxidation of fatty acids for the biosynthesis of leukotrienes and lipoxins. The structure of the 839-residue soybean lipoxygenase-1 was used as a template to model human 5-, 12-, and 15-lipoxygenases. A distance-based algorithm for placing side chains in a low homology environment (only the four iron ligands were fixed during side chain placement) was devised. Twenty-six of the 56 conserved lipoxygenase residues were grouped in four distinct regions of the enzyme. These regions were analyzed to discern whether the side chain interactions could be duplicated in the models or whether alternate conformers should be considered. The effects of site directed mutagenesis variants were rationalized using the models of the human lipoxygenases. In particular, variants which shifted positional specificity between 12- and 15-lipoxygenase activity were analyzed. Analysis of active site residues produced a model which accounts for observed lipoxygenase positional specificity and stereospecificity.

Crystallization and preliminary X-ray investigation of lipoxygenase-3 from soybeans

Soybean lipoxygenase-3 has been crystallized by the vapor diffusion method in 16-20% polyethylene glycol (average M(r), 3,400), 0.2 M sodium acetate buffer, pH 5.7, at 21 degrees C, at a protein concentration of 8-15 mg/mL. The crystals, which diffract to 3-A spacings, belong to the monoclinic space group C2. Cell constants are a = 111.9, b = 136.4, and c = 61.6 A and beta = 95.7 degrees. The calculated value of Matthews's constant, Vm = 2.48 A3/kDa, is consistent with the presence of one molecule of lipoxygenase per crystallographic asymmetric unit (Z = 4).

Primary structure of a lipoxygenase from barley grain as deduced from its cDNA sequence

A full length cDNA sequence for a barley grain lipoxygenase was obtained. It includes a 5' untranslated region of 69 nucleotides, an open reading frame of 2586 nucleotides encoding a protein of 862 amino acid residues and a 3' untranslated region of 142 nucleotides. The molecular mass of the encoded polypeptide was calculated to be 96.392. Its amino acid sequence shows a high homology with that of other plant lipoxygenases identified to date.

Position 713 is critical for catalysis but not iron binding in soybean lipoxygenase 3

The role of asparagine-713 in iron atom incorporation and catalysis in soybean lipoxygenase 3 was investigated using site-directed mutagenesis. A full-length cDNA for the lipoxygenase isoenzyme was obtained from a library derived from soybeans cv. Provar. Protein with native specific activity at pH 7.4 was obtained from expression in Escherichia coli. Two recent structure reports provided conflicting views about the participation of the side chain of asparagine-694 in the coordination of the iron atom required for catalysis by lipoxygenase 1. Oligonucleotide-directed mutagenesis was employed to modify residue 713 in lipoxygenase 3 which corresponds to asparagine-694 in the sequence of lipoxygenase 1. It was found that for enzyme expressed in bacteria, asparagine was not required for iron incorporation. Histidine, alanine, and serine substitutions for asparagine-713 all produced proteins that contained iron. The histidine mutant had specific activity and catalytic characteristics comparable to the wild-type enzyme. By contrast, the alanine- and serine-substituted lipoxygenases had no detectable catalytic activity. When oxidized by product, the histidine mutant also displayed the characteristic g6 signal of the soybean enzyme in its EPR spectrum. The possibilities that the residue at position 713 acts as a metal ligand, an acid-base catalyst, and a hydrogen bonding group are considered and discussed.

Structure of the Pisum sativum seed lipoxygenase gene lox1:Ps:3

We have isolated the Pisum sativum (pea) lox1:Ps:3 gene which encodes a lipoxygenase that is 84% identical in coding sequence to the LOX-3 gene from Glycine max (soybean). The 10028 bp sequence includes 5895 bp 5' to the transcription start site and 707 bp 3' to the stop codon. The coding region of lox1:Ps:3 contains eight introns, at positions equivalent to those in the soybean LOX-3 and L-4, the Phaseolus vulgaris (Frenchbean) LOX1, and the Pisum sativum lox1:Ps:2 genes. The first intron is unusually small. The 5'-flanking sequence contains two regions that have the potential to form hairpin structures, but few motifs known to interact with transcription factors. Despite their similarity in terms of expression, the lox1:Ps:3 and lox1:Ps:2 genes have little similarity within their 5'-flanking regions.

A single gene (Eu4) encodes the tissue-ubiquitous urease of soybean

We sought to determine the genetic basis of expression of the ubiquitous (metabolic) urease of soybean. This isozyme is termed the metabolic urease because its loss, in eu4/eu4 mutants, leads to accumulation of urea, whereas loss of the embryo-specific urease isozyme does not. The eu4 lesion eliminated the expression of the ubiquitous urease in vegetative and embryonic tissues. RFLP analysis placed urease clone LC4 near, or within, the Eu4 locus. Sequence comparison of urease proteins (ubiquitous and embryo-specific) and clones (LC4 and LS1) indicated that LC4 and LS1 encode ubiquitous and embryo-specific ureases, respectively. That LC4 is transcribed into poly(A)+ RNA in all tissues was indicated by the amplification of its transcript by an LC4-specific PCR primer. (The LS1-specific primer, on the other hand, amplified poly(A)+ RNA only from developing embryos expressing the embryo-specific urease.) These observations are consistent with Eu4 being the ubiquitous urease structural gene contained in the LC4 clone. In agreement with this notion, the mutant phenotype of eu4/eu4 callus was partially corrected by the LC4 urease gene introduced by particle bombardment.

Structure and sequence of the Arabidopsis thaliana lipoxygenase 1 gene

We have isolated and sequenced the Arabidopsis thaliana LOX1 gene which encodes a lipoxygenase. The 5255 bp sequence includes 763 bp upstream from the start codon, 4345 bp spanning the coding region and 147 bp downstream from the stop codon. The coding region of the LOX1 gene consists of 8 exons separated by 7 introns. The introns in the LOX1 gene are located in sites predicted by the closely related soybean seed LOX3 gene sequence. With the exception of intron 1, the LOX1 introns are smaller in size than the LOX3 introns. Furthermore the Arabidopsis gene contains 7 introns, while the soybean gene contains 8. Four putative TATA box elements were identified in the 763 bp sequence upstream from the coding region, however only one is followed by a cap site which is located in a position appropriate for it to act as the initiation site for transcription.

A survey of transcripts expressed specifically in root nodules of broadbean (Vicia faba L.)

More than 600 potentially nodule-specific clones have been detected by differential hybridization of a broadbean cDNA library constructed from root nodule poly(A)+ RNA. These isolated cDNAs belong to at least 28 different clone groups containing cross-hybridizing sequences. The number of clones within a clone group varies from about 200 to only one single clone. Northern hybridization experiments revealed nodule-specific transcripts for 14 clone groups and markedly nodule-enhanced transcripts for another 7 clone groups. Sequence homologies indicate that three transcript sequences code for different leghemoglobins. Two other transcripts encode a nodule-specific sucrose synthase and a nodule-enhanced asparagine synthetase, respectively. Four deduced gene products are proline-rich, two of them being the homologues of PsENOD2 and PsENOD12. The third proline-rich protein (PRP) is composed of similar amino acid repeats as the nodule-specific PsENOD12 but is expressed in nodules and roots in comparable amounts. The fourth PRP is a nodule-enhanced extensin-type protein built up by Ser-Pro4 repeats. Two further nodule-specific transcripts encode gene products showing some similarity to structural glycine-rich proteins. Additionally, transcripts could be identified for broadbean homologues of the nodulins MsNOD25, PsENOD3 and PsENOD5 and transcripts specifying a nodule-enhanced lipoxygenase and a translation elongation factor EF-1 alpha, which is expressed in all broadbean tissues tested.

Crystallographic determination of the active site iron and its ligands in soybean lipoxygenase L-1

Five ligands of the active site iron atom in soybean lipoxygenase L-1 have been identified from the electron density map of the crystallized enzyme. The position of the iron atom can be readily and independently located from an anomalous difference electron density map. The ligands identified are His-499, His-504, His-690, Asn-694, and Ile-839, the carboxy-terminal residue. Our previous view that these three histidines are essential for activity and binding of iron, based on site-specific mutation studies, is confirmed. A sixth protein ligand is not present, and the sixth coordination site opens into a wide cleft. The structure of the soybean lipoxygenase was solved by multiple anomalous isomorphous replacements.

Expression and secretion of pea-seed lipoxygenase isoenzymes in Saccharomyces cerevisiae

Lipoxygenases (EC 1.13.11.12) catalyse the oxygenation of polyunsaturated fatty acids such as linoleic and arachidonic acid into reactive cis/trans hydroperoxidiene intermediates, which then serve as substrates for other enzymes leading to the production of a variety of secondary metabolites. In order to explore the characteristics of the individual lipoxygenase isoenzymes in more detail larger amounts of the pure enzymes are needed and their production in a heterologous host is therefore desirable. Full-length cDNAs encoding pea-seed lipoxygenase isoenzymes 2 and 3 were expressed in Saccharomyces cerevisiae with the aid of yeast-Escherichia coli shuttle vectors. Expression of the cDNA for lipoxygenase 2 under the control of the constitutive phosphoglycerate kinase (PGK) gene promoter yielded significant amounts of active enzyme inside the cell, both with yeast transformants carrying the cDNA gene on high-copy-number plasmids or integrated in chromosome V. Addition of the yeast invertase signal sequence in front of the pea lipoxygenase 3 yielded secreted active pea-seed lipoxygenase in the medium, but large amounts of inactive lipoxygenase 3 remained inside the yeast cell. Expression of the LOX3 cDNA can be achieved either constitutively with the PGK promoter or inducibly with the GAL1 promoter.

Molecular evolution of cyclooxygenase and lipoxygenase

Four oxygenases of the arachidonic acid cascade (cyclooxygenase, 5-lipoxygenase, 12-lipoxygenase and 15-lipoxygenase) were investigated by the method of computer-assisted sequence comparison. From the calculations, some aspects of evolution and function of these enzymes were revealed. (1) The evolutionary origin of cyclooxygenase was different from that of lipoxygenases. (2) Cyclooxygenase was a distantly related member of a peroxidase family. (3) Enzymes with 12-lipoxygenase activity were created independently twice by gene duplication.

Identification of the iron-binding histidine residues in soybean lipoxygenase L-1

Lipoxygenases constitute a class of non-heme, non-sulfur iron dioxygenases acting upon lipids possessing a 1,4-cis-cis-pentadiene moiety. The iron is known to be essential for activity. A motif of six histidine residues has been found in all of the thirteen lipoxygenases, from both plant and animal sources, whose sequences have been reported. We had previously obtained mutant proteins in which each of the 6 conserved histidines of soybean lipoxygenase L-1 had been replaced and found that the mutants H499Q, H504Q (or H504S) and H690Q had no detectable enzymatic activity. We have now found that these inactive proteins contain no Fe, although they have the same electrophoretic mobility as wild-type L-1 under both denaturing and non-denaturing conditions and react with anti-L-1 antibodies.

cDNA cloning of rice lipoxygenase L-2 and characterization using an active enzyme expressed from the cDNA in Escherichia coli

A full-length cDNA of rice lipoxygenase L-2 was cloned from 3-day-old seedlings. The identity of the clone was determined by amino acid sequencing of selected peptides of the purified enzyme and immunological characterization of an active enzyme that was produced from the cDNA in Escherichia coli by cultivation at 15 degrees C. The nucleotide sequence showed a strong bias toward G and C in the selection of nucleotides, especially at the third position of the codons (93% G/C). The complete amino acid sequence of the enzyme was deduced from the nucleotide sequence. The molecular mass of the enzyme was calculated to be 96,657 Da based on 865 amino acids. The amino acid sequence shares similarity with those of dicot lipoxygenases throughout the enzyme at a level of 50%. A hydropathy profile calculated from the amino acid sequence resembled those of dicot lipoxygenases, suggesting conservation of the secondary structure of these enzymes. The active enzyme, expressed in Escherichia coli, was characterized for pH dependence of the enzyme activity, intramolecular specificity, heat stability and Km. The enzyme had the same properties as the L-2 enzyme that was isolated from seedlings, but differed from the lipoxygenase L-3 isolated from mature plants.

Conserved histidine residues in soybean lipoxygenase: functional consequences of their replacement

Sequences of 13 lipoxygenases from various plant and mammalian species, thus far reported, display a motif of 38 amino acid residues which includes 5 conserved histidines and a 6th histidine about 160 residues downstream. These residues occur at positions 494, 499, 504, 522, 531, and 690 in soybean lipoxygenase isozyme L-1. Since the participation of iron in the lipoxygenase reaction has been established and existing evidence based on Mössbauer and EXAFS spectroscopy suggests that histidines may be involved in iron binding, the effect of the above residues has been examined in soybean lipoxygenase L-1. Six singly mutated lipoxygenases have been produced in which each of the His residues has been replaced with glutamine. Two additional mutants have been constructed wherein the codons for His-494 and His-504 have been replaced by serine codons. All of the mutant lipoxygenases, which were obtained by expression in Escherichia coli, have mobilities identical to that of the wild-type enzyme on denaturing gel electrophoresis and respond to lipoxygenase antibodies. The mutated proteins H499Q, H504Q, H504S, and H690Q are virtually inactive, while H522Q has about 1% of the wild-type activity. H494Q, H494S, and H531Q are about 37%, 8%, and 20% as active as the wild type, respectively. His-517 is conserved in the several lipoxygenase isozymes but not in the animal isozymes. The mutant H517Q has about 33% of the wild-type activity. The inactive mutants, H499Q, H504Q, H504S, and H690Q, become insoluble when heated for 3 min at 65 degrees C, as does H522Q. The other mutants and the wild-type are stable under these conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of soybean lipoxygenase-1 by n-alcohols and n-alkylthiols

A series of n-alcohols and n-alkylthiols with carbon chains from 2 to 12 were examined for the inhibition of soybean lipoxygenase-1 (L-1). The alcohol produces a competitive inhibition, the extent of which increases with an increase in the carbon number of alkyl chain up to 8. Whereas the inhibition of the alkylthiol is noncompetitive, the extent of which is almost independent from the carbon number. From the behavior of pKi dependence on the carbon number of the alcohol, the decyl group appears to be optimum to bind to L-1. The thermodynamic analysis for the inhibition based upon van 't Hoff equation indicates positive enthalpy and entropy changes for the binding of the alcohol to the enzyme and negative enthalpy and positive to negative entropy changes for that of the alkylthiol. These observations suggest that the alcohol inhibits L-1 by binding of the hydrophobic alkyl tail to the catalytic site of the enzyme by a hydrophobic interaction. The alkylthiol inhibits by binding of the nucleophilic sulfhydryl head to a polarizable region of the enzyme and the alkyl tail to a hydrophobic region of the enzyme free from the steric hindrance as an anchor.

A lipoxygenase is the main lipid body protein in cucumber and soybean cotyledons during the stage of triglyceride mobilization

The 90-kDa lipid body protein characterized earlier by its high expression during the stage of fat degradation was identified as a form of lipoxygenase. This organelle form was compared with lipoxygenase species purified from the cytosol. It is further shown that the antibodies raised against the lipid body membrane lipoxygenase from cucumber cotyledons cross-react with both cytosolic and lipid body lipoxygenase from soybean.

Mutagenesis studies on the amino acid residues involved in the iron-binding and the activity of human 5-lipoxygenase

Human 5-lipoxygenase contains a non-heme iron essential for its activity. In order to determine which amino acid residues are involved in the iron-binding and the lipoxygenase activity, nine amino acid residues in highly homologous regions among the lipoxygenases were individually replaced by means of site-directed mutagenesis. Mutant 5-lipoxygenases in which His-367 or His-550 was replaced by either Asn or Ala, His-372 by either Asn or Ser, or Glu-376 by Gln were completely devoid of the activity. Though mutants containing an alanine residue instead of His-390 or His-399 lacked the activity, the corresponding asparagine substituted mutants exhibited. The other mutants retained the enzyme activity. These results strongly suggest that His-367, His-372, His-550 and Glu-376 are crucial for 5-lipoxygenase activity and coordinate to the essential iron.

Purification of two forms of arachidonate 15-lipoxygenase from human leukocytes

Two different proteins with arachidonate 15-lipoxygenase activity have been purified to near homogeneity from human leukocytes. Both have the same molecular mass (74 kDa) on SDS/PAGE and appear to be equally active with three different fatty acid substrates. The N-terminal amino acid sequences of both forms were identical to the sequence of human reticulocyte 15-lipoxygenase [Sigal, E., Craik, C.S., Highland, E., Grunberger, D., Costello, L.L., Dixon, R.A.F. & Nadel, J.A. (1988) Biochem. Biophys. Res. Commun. 157, 457-464]. The two forms of 15-lipoxygenase could be clearly separated by cation-exchange chromatography. Of particular interest, the relative amounts of the two forms differed markedly between leukocytes obtained from normal donors and leukocytes from an individual with eosinophilia.

Lipoxygenase gene expression is modulated in plants by water deficit, wounding, and methyl jasmonate

Two classes of lipoxygenase (LOX) cDNAs, designated loxA and loxB, were isolated from soybean. A third lipoxygenase cDNA, loxP1, was isolated from pea. The deduced amino acid sequences of loxA and loxB show 61-74% identity with those of soybean seed LOXs. loxA and loxB mRNAs are abundant in roots and non-growing regions of seedling hypocotyls. Lower levels of these mRNAs are found in hypocotyl growing regions. Exposure of soybean seedlings to water deficit causes a rapid increase in loxA and loxB mRNAs in the elongating hypocotyl region. Similarly, loxP1 mRNA levels increase rapidly when pea plants are wilted. loxA and loxB mRNA levels also increase in wounded soybean leaves, and these mRNAs accumulate in soybean suspension cultures treated with 20 microM methyl jasmonate. These results demonstrate that LOX gene expression is modulated in response to water deficit and wounding and suggest a role for lipoxygenase in plant responses to these stresses.