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

Genome Survey and Chromosome-Level Draft Genome Assembly of Glycine max var. Dongfudou 3: Insights into Genome Characteristics and Protein Deficiencies

Dongfudou 3 is a highly sought-after soybean variety due to its lack of beany flavor. To support molecular breeding efforts, we conducted a genomic survey using next-generation sequencing. We determined the genome size, complexity, and characteristics of Dongfudou 3. Furthermore, we constructed a chromosome-level draft genome and speculated on the molecular basis of protein deficiency in GmLOX1, GmLOX2, and GmLOX3. These findings set the stage for high-quality genome analysis using third-generation sequencing. The estimated genome size is approximately 1.07 Gb, with repetitive sequences accounting for 72.50%. The genome is homozygous and devoid of microbial contamination. The draft genome consists of 916.00 Mb anchored onto 20 chromosomes, with annotations of 46,446 genes and 77,391 transcripts, achieving Benchmarking Single-Copy Orthologue (BUSCO) completeness of 99.5% for genome completeness and 99.1% for annotation. Deletions and substitutions were identified in the three GmLox genes, and they also lack corresponding active proteins. Our proposed approach, involving k-mer analysis after filtering out organellar DNA sequences, is applicable to genome surveys of all plant species, allowing for accurate assessments of size and complexity. Moreover, the process of constructing chromosome-level draft genomes using closely related reference genomes offers cost-effective access to valuable information, maximizing data utilization.

Genome-wide identification and analysis of LOX genes in soybean cultivar “Zhonghuang 13”

Lipoxygenases (LOXs; EC1.13.11.12) are a family of iron- or manganese-containing dioxygenases that catalyze the oxygenation of polyunsaturated fatty acids (PUFAs) and play important roles in plant growth, development, and stress response. In this study, a total of 36 LOX gene family members were identified and annotated in Zhonghuang 13, a soybean cultivar bred by Chinese scientists in 2001. Sanger sequencing of the GmLOX1-coding sequence and colorimetric assays for the GmLOX1 protein showed that Zhonghuang 13 possessed the GmLOX1 gene. These LOX genes are divided into three subfamilies: 9-LOX, type Ⅰ 13-LOX and type II 13-LOX. In the 13-LOX group, the number of GmLOX members was the highest. These GmLOX genes are unevenly distributed on chromosomes 3, 7, 8, 10, 11, 12, 13, 15, 16, 19, and 20. Most of the 13-LOX genes exist in the form of gene clusters, indicating that these genes may originate from tandem duplications. The analysis of duplicated gene pairs showed that GmLOX genes underwent purifying selective pressure during evolution. The gene structures and conserved functional domains of these genes are quite similar. Compared to the orthologous gene pairs of LOX genes between wild soybean (Glycine soja W05) and Zhonghuang 13, the sequences of most gene pairs are relatively conserved. Many cis-elements are present in the promoter region and are involved in stress response, growth and development, hormone response and light response. The tissue-specific gene expression of GmLOX genes was evaluated. Represented by GmLOX1, GmLOX2, and GmLOX3, which were expressed at extremely high levels in seeds, they showed the characteristics of specific expression. This study provides detailed information on soybean lipoxygenase gene family members in Zhonghuang 13, which lays a foundation for further research.

Genome-wide identification and expression pattern analysis of lipoxygenase gene family in turnip (Brassica rapa L. subsp. rapa)

Turnip (Brassica rapa L. subsp. rapa) is an important crop with edible and medicinal values, and various stresses, especially salt stress and drought stress, seriously threaten the yield of turnips. LOXs play important roles in regulating plant growth and development, signal transduction, and biotic and abiotic stress responses through secondary metabolites produced by the oxylipin metabolic pathway, and although the turnip genome has been published, however, the role of LOX family genes in various abiotic stress responses has not been systematically studied in turnips. In this study, a total of 15 LOX genes (BrrLOX) were identified in turnip, distributed on six chromosomes. Phylogenetic tree analysis classified these LOX genes into two classes: three 9-LOX proteins and 12 13-LOX type II proteins. Gene duplication analysis showed that tandem and segmental duplication were the main pathways for the expansion of the BrrLOX gene family. The Ka and Ks values of the duplicated genes indicate that the BrrLOX gene underwent strong purifying selection. Further analysis of the cis-acting elements of the promoters suggested that the expression of the BrrLOX gene may be influenced by stress and phytohormones. Transcriptome data analysis showed that 13 BrrLOX genes were expressed at one or more stages of turnip tuber development, suggesting that LOX genes may be involved in the formation of turnip fleshy roots. The qRT-PCR analysis showed that four stresses (salt stress, drought stress, cold stress, and heat stress) and three hormone treatments (methyl jasmonate, salicylic acid, and abscisic acid) affected the expression levels of BrrLOX genes and that different BrrLOX genes responded differently to these stresses. In addition, weighted gene co-expression network analysis (WGCNA) of BrrLOX revealed seven co-expression modules, and the genes in these co-expression modules are collectively involved in plant growth and development and stress response processes. Thus, our results provide valuable information for the functional identification and regulatory mechanisms of BrrLOX in turnip growth and development and stress response.

The acceleration of yellow lupine flower abscission by jasmonates is accompanied by lipid-related events in abscission zone cells

Yellow lupine is an economically important crop. This species has been used as a great model for abscission processes for several years due to extreme flower abortion, which takes place in the abscission zone (AZ). AZ activation involves modifications of cell walls, membranes, and cellular structure. In this paper, we applied physiological, molecular, biochemical, and instrumental methods to explore lipid-associated changes and the possible involvement of lipid-derived phytohormones - jasmonates (JAs) - in flower AZ activation. Our comprehensive analyses revealed that natural abscission is accompanied by the upregulation of peroxidase, which reflects a disruption of redox balance and/or lipids peroxidation in AZ cell membranes. Redox imbalance was confirmed by appearance of malondialdehyde. Lipid-related processes involved the specific localization and increased level and activity of lipase and LOX, enzymes associated with cell membrane rupture, and JA biosynthesis. Lipid-hydrolyzing phospholipase D, implicated previously in abscission, is also found in naturally active AZs. Observed changes are accompanied by the accumulation of jasmonates, both free jasmonic acid and its methyl ester. The JA derivative exhibited higher biological activity than the nonconjugated form. Overall, our study shed new light on the lipid and phytohormonal regulation of AZ functioning supporting a role of JAs during abscission-associated events.

Identification of a Prenyl Chalcone as a Competitive Lipoxygenase Inhibitor: Screening, Biochemical Evaluation and Molecular Modeling Studies

Cyclooxygenase (COX) and lipoxygenase (LOX) are key targets for the development of new anti-inflammatory agents. LOX, which is involved in the biosynthesis of mediators in inflammation and allergic reactions, was selected for a biochemical screening campaign to identify LOX inhibitors by employing the main natural product library of Brazilian biodiversity. Two prenyl chalcones were identified as potent inhibitors of LOX-1 in the screening. The most active compound, (E)-2-O-farnesyl chalcone, decreased the rate of oxygen consumption to an extent similar to that of the positive control, nordihydroguaiaretic acid. Additionally, studies on the mechanism of the action indicated that (E)-2-O-farnesyl chalcone is a competitive LOX-1 inhibitor. Molecular modeling studies indicated the importance of the prenyl moieties for the binding of the inhibitors to the LOX binding site, which is related to their pharmacological properties.

Genome-wide identification and classification of Lipoxygenase gene family and their roles in sorghum-aphid interaction

This report shows detailed characterization of LOX gene family in sorghum and provides new insight of sorghum LOX genes in genetic structure and their roles in plant response to infestation by sugarcane aphids. Lipoxygenases (LOXs) are monomeric, nonheme iron-containing dioxygenases that initiate the fatty acid oxidation pathway creating oxylipins and plant hormone jasmonate both have a key role in plant development and defense. To date, a comprehensive and systematic analysis of sorghum LOXs is still deficient. Thus, we performed a genome-wide analysis of the sorghum LOXs genome and identified nine LOXs genes. Detailed examination of protein sequences and phylogenetic analysis categorized the sorghum LOXs into two subclasses, 9-LOXs (SbLOX1, SbLOX3, SbLOX4, SbLOXm, and SbLOXo), 13-LOXs (SbLOX9, SbLOX5, and SbLOX2), and the unclassified SbLOX8. This classification was further supported by sequence similarity/identity matrix and subcellular localization analysis. The lipoxygenase domains, motifs, and vital amino acids were highly conserved in all sorghum LOX genes. In silico analysis of the promoter region of SbLOXs identified different hormones responsive cis-elements. Furthermore, to explore the roles of sorghum LOXs during sugarcane aphid feeding and exogenous MeJA application, expression analysis was conducted for all the eight LOXs in resistant (Tx2783) and susceptible (Tx7000) sorghum lines, respectively. As detailed in this report, the data generated from both genome-wide identification and expression analysis of lipoxygenase genes suggest the putative functions of two 13-LOXs (SbLOX9 and SbLOX5) and three 9-LOXs (SbLOX1, SbLOX3, and SbLOXo) in biosynthesis of jasmonic acid, green leaf volatiles and death acids, and all of them are involved in defense-related functions in plants. Furthermore, this report represents the first genome-wide analysis of the LOX gene family in sorghum, which will facilitate future studies to characterize the roles of each individual LOXs gene in aphid resistance and defense responses to other stresses.

Mobilization of storage lipid reserve and expression analysis of lipase and lipoxygenase genes in rice (Oryza sativa var. Pusa Basmati 1) bran during germination

Storage lipid mobilization by lipases and lipoxygenases (LOXs) in response to developmental cues take place during seed germination. After rice grain milling, the endogenous lipases and LOXs present in the bran fraction come in contact with the storage lipid reserve or triacylglycerol (TAG). Lipases catalyze the hydrolysis of TAGs to non-esterified fatty acids (NEFAs) and glycerol. The NEFAs, especially linoleic acid (18:2) produced, are further subjected to oxidative rancidity via peroxidation reaction catalyzed by LOXs. This results in the production of conjugated hydroperoxides of 18:2 that influence the off-flavors in rice bran lipids. The aim of this study is to understand how lipid mobilization and expression of lipase and LOX genes occur in the bran of germinating rice grains (Oryza sativavar. Pusa Basmati 1). Our results show that the primary source of storage lipids in bran is TAG, and its mobilization starts at 4 days after imbibition (4 DAI). Using publically available RNA-seq data and phylogeny analyses, we selected a total of 18 lipase and 16 LOX genes in rice for their expression profiles during onset of lipid mobilization. Gene expression analyses revealed OsLip1, OsLip9, and OsLip13; and OsLOX3 and OsLOX14 as the predominantly expressed genes in bran of germinating rice grains. This study explores two important events in the germinating rice grains, namely, mobilization of storage lipids and expression pattern of lipase and LOX genes. The information generated in this study can be used to efficiently manipulate the genes to enhance the shelf-stability of bran lipid reserve.

Genome-wide identification of tomato (Solanum lycopersicum L.) lipoxygenases coupled with expression profiles during plant development and in response to methyl-jasmonate and wounding

Lipoxygenases (LOXs) (EC 1.13.11.12) catalyze the oxygenation of fatty acids and produce oxylipins including the plant hormone jasmonate (jasmonic acid/methyl jasmonate; MeJA). Little is known about the tomato LOX gene family members that impact tomato growth and development, and less so about their feed-back regulation in response to MeJA. We present genome wide identification of 14 LOX gene family members in tomato which map unevenly on 12 chromosomes. The characteristic structural features of 9-LOX and 13-LOX tomato gene family, their protein domains/features, and divergence are presented. Quantification of the expression patterns of all the 14 SlLOX gene members segregated the members based on differential association with growth, development, or fruit ripening. We also identified those SlLOX genes whose transcription responds to exogenous MeJA and/or wounding stress. MeJA-based feedback regulation that involves activation of specific members of LOX genes is defined. Specific nature of SlLOX gene regulation in tomato is defined. The novel data on dynamics of SlLOX gene expression should help catalyze future strategies to elucidate role(s) of each gene member in planta and for crop biotechnological intervention.

Genome-wide identification, classification and expression of lipoxygenase gene family in pepper

KEY MESSAGE

Lipoxygenases mediate important biological processes. Through comparative genomics, domain-scan analysis, sequence analysis, phylogenetic analysis, homology modelling and transcriptional analysis the lipoxygenase gene family of pepper (Capsicum annuum) has been identified. Lipoxygenases (LOXs) are non-heme, iron-containing dioxygenases playing a pivotal role in diverse biological processes in plants, including defence and development. Here, we exploited the recent sequencing of the pepper genome to investigate the LOX gene family in pepper. Two LOX classes are recognized, the 9- and 13-LOXs that oxygenate lipids at the 9th and 13th carbon atom, respectively. Using two main in-silico approaches, we identified a total of eight LOXs in pepper. Phylogenetic analysis classified four LOXs (CaLOX1, CaLOX3, CaLOX4 and CaLOX5) as 9-LOXs and four (CaLOX2, CaLOX6, CaLOX7 and CaLOX8) as 13-LOXs. Furthermore, sequence similarity/identity and subcellular localization analysis strengthen the classification predicted by phylogenetic analysis. Pivotal amino acids together with all domains and motifs are highly conserved in all pepper LOXs. Expression of 13-LOXs appeared to be more dynamic compared to 9-LOXs both in response to exogenous JA application and to thrips feeding. Bioinformatic and expression analyses predict the putative functions of two 13-LOXs, CaLOX6 and CaLOX7, in the biosynthesis of Green Leaf Volatiles, involved in indirect defence. The data are discussed in the context of LOX families in solanaceous plants and plants of other families.

Patatin-like phospholipases in microbial infections with emerging roles in fatty acid metabolism and immune regulation by Apicomplexa

Emerging lipidomic technologies have enabled researchers to dissect the complex roles of phospholipases in lipid metabolism, cellular signaling and immune regulation. Host phospholipase products are involved in stimulating and resolving the inflammatory response to pathogens. While many pathogen-derived phospholipases also manipulate the immune response, they have recently been shown to be involved in lipid remodeling and scavenging during replication. Animal and plant hosts as well as many pathogens contain a family of patatin-like phospholipases, which have been shown to have phospholipase A₂ activity. Proteins containing patatin-like phospholipase domains have been identified in protozoan parasites within the Apicomplexa phylum. These parasites are the causative agents of some of the most widespread human diseases. Malaria, caused by Plasmodium spp., kills nearly half a million people worldwide each year. Toxoplasma and Cryptosporidium infect millions of people each year with lethal consequences in immunocompromised populations. Parasite-derived patatin-like phospholipases are likely effective drug targets and progress in the tools available to the Apicomplexan field will allow for a closer look at the interplay of lipid metabolism and immune regulation during host infection.

Identification of lipoxygenase (LOX) genes from legumes and their responses in wild type and cultivated peanut upon Aspergillus flavus infection

Lipoxygenase (LOX) genes are widely distributed in plants and play crucial roles in resistance to biotic and abiotic stress. Although they have been characterized in various plants, little is known about the evolution of legume LOX genes. In this study, we identified 122 full-length LOX genes in Arachis duranensis, Arachis ipaënsis, Cajanus cajan, Cicer arietinum, Glycine max, Lotus japonicus and Medicago truncatula. In total, 64 orthologous and 36 paralogous genes were identified. The full-length, polycystin-1, lipoxygenase, alpha-toxin (PLAT) and lipoxygenase domain sequences from orthologous and paralogous genes exhibited a signature of purifying selection. However, purifying selection influenced orthologues more than paralogues, indicating greater functional conservation of orthologues than paralogues. Neutrality and effective number of codons plot results showed that natural selection primarily shapes codon usage, except for C. arietinum, L. japonicas and M. truncatula LOX genes. GCG, ACG, UCG, CGG and CCG codons exhibited low relative synonymous codon usage (RSCU) values, while CCA, GGA, GCU, CUU and GUU had high RSCU values, indicating that the latter codons are strongly preferred. LOX expression patterns differed significantly between wild-type peanut and cultivated peanut infected with Aspergillus flavus, which could explain the divergent disease resistance of wild progenitor and cultivars.

Retention and Molecular Evolution of Lipoxygenase Genes in Modern Rosid Plants

Whole-genome duplication events have occurred more than once in the genomes of some rosids and played a significant role over evolutionary time. Lipoxygenases (LOXs) are involved in many developmental and resistance processes in plants. Our study concerns the subject of the LOX gene family; we tracked the evolutionary process of ancestral LOX genes in four modern rosids. Here we show that some members of the LOX gene family in the Arabidopsis genome are likely to be lost during evolution, leading to a smaller size than that in Populus, Vitis, and Carica. Strong purifying selection acted as a critical role in almost all of the paralogous and orthologous genes. The structure of LOX genes in Carica and Populus are relatively stable, whereas Vitis and Arabidopsis have a difference. By searching conserved motifs of LOX genes, we found that each sub-family shared similar components. Research on intraspecies gene collinearity show that recent duplication holds an important position in Populus and Arabidopsis. Gene collinearity analysis within and between these four rosid plants revealed that all LOX genes in each modern rosid were the offspring from different ancestral genes. This study traces the evolution of LOX genes which have been differentially retained and expanded in rosid plants. Our results presented here may aid in the selection of special genes retained in the rosid plants for further analysis of biological function.

The Lipoxygenase Gene Family in Poplar: Identification, Classification, and Expression in Response to MeJA Treatment

Background

Lipoxygenases (LOXs) are important dioxygenases in cellular organisms. LOXs contribute to plant developmental processes and environmental responses. However, a systematic and comprehensive analysis has not been focused on the LOX gene family in poplar. Therefore, in the present study, we performed a comprehensive analysis of the LOX gene family in poplar.

Results

Using bioinformatics methods, we identified a total of 20 LOX genes. These LOX genes were clustered into two subfamilies. The gene structure and motif composition of each subfamily were relatively conserved. These genes are distributed unevenly across nine chromosomes. The PtLOX gene family appears to have expanded due to high tandem and low segmental duplication events. Microarray analysis showed that a number of PtLOX genes have different expression pattern across disparate tissues and under various stress treatments. Quantitative real-time PCR (qRT-PCR) analysis was further performed to confirm the responses to MeJA treatment of the 20 poplar LOX genes. The results show that the PtLOX genes are regulated by MeJA (Methyl jasmonate) treatment.

Conclusions

This study provides a systematic analysis of LOX genes in poplar. The gene family analysis reported here will be useful for conducting future functional genomics studies to uncover the roles of LOX genes in poplar growth and development.

Nonthermal inactivation of soy (Glycine max Sp.) lipoxygenase by pulsed ultraviolet light

This study investigated pulsed ultraviolet (PUV) illumination at different distances from the PUV source on soybean lipoxygenase (LOX) (0.4 mg/mL in 0.01 M Tris-HCl buffer, pH 9) activity. Samples (5 mL) were illuminated for 1, 2, 4, 8, and 16 s at 3 distances 6, 8.5, and 11 cm from the PUV lamp's quartz window. The temperature of 33.5 ± 1.8°C was observed for the highest treatment time of 16 s at the shortest distance of 6 cm, and resulted in a 3.5 log reduction (99.95%) in initial LOX activity. Illumination time and distance from the lamp significantly (P ≤ 0.05) affected LOX inactivation. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) was performed on treated LOX samples and further protein profile for treated LOX filtrate (≤10 kDa), was analyzed by reverse phase high-performance liquid chromatography (RP-HPLC). The protein profile analysis revealed that LOX protein degradation was influenced significantly (P ≤ 0.05) by PUV illumination time.

Molecular sequence variations of the lipoxygenase-2 gene in soybean

Soybean lipoxygenase genes comprise a multi-gene family, with the seed lipoxygenase isozymes LOX1, LOX2, and LOX3 present in soybean seeds. Among these, the LOX2 isozyme is primarily responsible for the "beany" flavor of most soybean seeds. The variety, Jinpumkong 2, having null alleles (lx1, lx2, and lx3) lacks the three seed lipoxygenases; so, sequence variations between the lipoxygenase-2 genes of Pureunkong (Lx2) and Jinpumkong 2 (lx2) cultivars were examined. One indel, four single nucleotide polymorphisms (SNPs), a 175-bp fragment in the 5'-flanking sequence, and a missense mutation within the coding region were found in Jinpumkong 2. The distribution of the sequence variations was investigated among 90 recombinant inbred lines (RILs) derived from a cross of Pureunkong × Jinpumkong 2 and in 480 germplasm accessions with various origins and maturity groups. Evidence for a genetic bottleneck was observed: the 175-bp fragment was rare in Glycine max, but present in the majority of the G. soja accessions. Furthermore, the 175-bp fragment was not detected in the 5' upstream region of the Lx2 gene on chromosome (Chr) 13 in Williams 82; instead, a similar 175-bp fragment was positioned in the homeologous region on Chr 15. The findings indicated that the novel fragment identified was originally present in the Lx2 region prior to the recent genome duplication in soybean, but became rare in the G. max gene pool. The missense mutation of the conserved histidine residue of the lx2 allele was developed into a single nucleotide-amplified polymorphism (SNAP) marker. The missense mutation showed a perfect correlation with the LOX2-lacking phenotype, so the SNAP marker is expected to facilitate breeding of soybean cultivars which lack the LOX2 isozyme.

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.

Comparative molecular and biochemical characterization of segmentally duplicated 9-lipoxygenase genes ZmLOX4 and ZmLOX5 of maize

Lipoxygenases (LOXs) catalyze hydroperoxidation of polyunsaturated fatty acids (PUFAs) to form structurally and functionally diverse oxylipins. Precise physiological and biochemical functions of individual members of plant multigene LOX families are largely unknown. Herein we report on molecular and biochemical characterization of two closely related maize 9-lipoxygenase paralogs, ZmLOX4 and ZmLOX5. Recombinant ZmLOX5 protein displayed clear 9-LOX regio-specificity at both neutral and slightly alkaline pH. The genes were differentially expressed in various maize organs and tissues as well as in response to diverse stress treatments. The transcripts of ZmLOX4 accumulated predominantly in roots and shoot apical meristem, whereas ZmLOX5 was expressed in most tested aboveground organs. Both genes were not expressed in untreated leaves, but displayed differential induction by defense-related hormones. While ZmLOX4 was only induced by jasmonic acid (JA), the transcripts of ZmLOX5 were increased in response to JA and salicylic acid treatments. ZmLOX5 was transiently induced both locally and systemically by wounding, which was accompanied by increased levels of 9-oxylipins, and fall armyworm herbivory, suggesting a putative role for this gene in defense against insects. Surprisingly, despite of moderate JA- and wound-inducibility of ZmLOX4, the gene was not responsive to insect herbivory. These results suggest that the two genes may have distinct roles in maize adaptation to diverse biotic and abiotic stresses. Both paralogs were similarly induced by virulent and avirulent strains of the fungal leaf pathogen Cochliobolus carbonum. Putative physiological roles for the two genes are discussed in the context of their biochemical and molecular properties.

Molecular analysis of lipoxygenases associated with nodule development in soybean

We utilized transcriptional profiling to identify genes associated with nodule development in soybean. Many of the candidate genes were predicted to be involved in processes such as defense, metabolism, transcriptional regulation, oxidation, or iron storage. Here, we describe the detailed characterization of one specific class of genes that encode the enzyme lipoxygenase (LOX). The LOX9 and LOX10 genes identified by microarray analysis represent novel soybean LOXs expressed in developing nodules. LOX expression during nodulation was relatively complex, with at least eight different LOX genes expressed in soybean nodules. Histochemical analyses utilizing LOX9 promoter::beta-glucuronidase (GUS) fusion constructs in transgenic soybean hairy roots suggest that this gene is involved in the growth and development of specific cells within the root and nodules. In soybean roots, LOX9 was expressed specifically in the developing phloem. In nodules, the expression of LOX9 was correlated with the development of cells in the vasculature and lenticels. The use of RNAi in transgenic hairy roots reduced LOX expression by approximately 95%. Despite this significant reduction in LOX expression, there was no detectable effect on the development of roots or nodules. Our findings are discussed with respect to the potential function of LOXs in nodulation.

The 9-lipoxygenase GhLOX1 gene is associated with the hypersensitive reaction of cotton Gossypium hirsutum to Xanthomonas campestris pv malvacearum

Hypersensitive reaction (HR) cell death of cotton to the incompatible race 18 from Xanthomonas campestris pathovar malvacearum (Xcm) is associated with 9S-lipoxygenase activity (LOX) responsible for lipid peroxidation. Here, we report the cloning of cotton (Gossypium hirsutum L.) LOX gene (GhLOX1) and the sequencing of its promoter. GhLOX1 was found to be highly expressed during Xcm induced HR. Sequence analysis showed that GhLOX1 is a putative 9-LOX, and GhLOX1 promoter contains SA and JA responsive elements. Investigation on LOX signalisation on cotyledons infiltrated with salicylic acid (SA), or incubated with methyl-jasmonate (MeJA) revealed that both treatments induced LOX activity and GhLOX1 gene expression. HR-like symptoms were observed when LOX substrates were then injected in treated (MeJA and SA) cotyledons or when Xcm compatible race 20 was inoculated on MeJA treated cotyledons. Together these results support the fact that GhLOX1 encodes a 9 LOX whose activity would be involved in cell death during cotton HR.

Aspergillus infection inhibits the expression of peanut 13S-HPODE-forming seed lipoxygenases

Oxylipins recently have been implicated as signaling molecules for cross-kingdom communication in plant-pathogen interactions. Linoleic acid and its two plant lipoxygenase (LOX) oxylipin products 9- and 13-hydroperoxy fatty acids (9S- and 13S-HPODE) have been shown to have a significant effect on differentiation processes in the mycotoxigenic seed pathogens Aspergillus spp. Whereas both fatty acids promote sporulation, 9S-HPODE stimulates and 13S-HPODE inhibits mycotoxin production. Additionally, Aspergillus flavus infection of seed promotes linoleate 9-LOX expression and 9S-HPODE accumulation. Here, we describe the characterization of two peanut seed lipoxygenase alleles (PnLOX2 and PnLOX3) highly expressed in mature seed. PnLOX2 and PnLOX3 both are 13S-HPODE producers (linoleate 13-LOX) and, in contrast to previously characterized 9-LOX or mixed function LOX genes, are repressed between 5-fold and 250-fold over the course of A. flavus infection. The results of these studies suggest that 9S-HPODE and 13S-HPODE molecules act as putative susceptibility and resistance factors respectively, in Aspergillus seed-aflatoxin interactions.

Stability of immobilized soybean lipoxygenases: influence of coupling conditions on the ionization state of the active site Fe

The potential application of lipoxygenase as a versatile biocatalyst in enzyme technology is limited by its poor stability. Two types of soybean lipoxygenases, lipoxygenase-1 and -2 (LOX-1 and LOX-2) were purified by a two step anion exchange chromatography. Four different commercially available supports: CNBr Sepharose 4B, Fractogel((R)) EMD Azlactone, Fractogel((R)) EMD Epoxy, and Eupergit((R)) C were tested for immobilization and stabilization of the purified isoenzymes. Both isoenzymes gave good yields in enzyme activity and good stability after immobilization on CNBr Sepharose 4B and Fractogel((R)) EMD Azlactone. Rapid decay in activity associated with change in the ionization state of Fe, as shown by EPR measurements was observed within the first 5 days after immobilization on epoxy activated supports (Eupergit((R)) C and Fractogel((R)) EMD Epoxy) in high ionic strength buffers. Stabilization of the biocatalyst on these supports was achieved by careful adjustment of the immobilization conditions. When immobilized in phosphate buffer of pH 7.5 and low ionic strength (0.05 M), the half-life time of the immobilized enzyme increased 20 fold. The dependence of the stability of LOX immobilized on epoxy activated supports on the coupling conditions was attributed to a modulation of the ligand environment of the iron in the active site and consequently its reactivity.

Mutagenesis and modelling of linoleate-binding to pea seed lipoxygenase

We have produced a model to define the linoleate-binding pocket of pea 9/13-lipoxygenase and have validated it by the construction and characterization of eight point mutants. Three of the mutations reduced, to varying degrees, the catalytic centre activity (kcat) of the enzyme with linoleate. In two of the mutants, reductions in turnover were associated with changes in iron-coordination. Multiple sequence alignments of recombinant plant and mammalian lipoxygenases of known positional specificity, and the results from numerous other mutagenesis and modelling studies, have been combined to discuss the possible role of the mutated residues in pea 9/13-lipoxygenase catalysis. A new nomenclature for recombinant plant lipoxygenases based on positional specificity has subsequently been proposed. The null-effect of mutating pea 9/13-lipoxygenase at the equivalent residue to that which controlled dual positional specificity in cucumber 13/9-lipoxygenase, strongly suggests that the mechanisms controlling dual positional specificity in pea 9/13-lipoxygenase and cucumber 13/9-lipoxygenase are different. This was supported from modelling of another isoform of pea lipoxygenase, pea 13/9-lipoxygenase. Dual positional specificity in pea lipoxygenases is more likely to be determined by the degree of penetration of the methyl terminus of linoleate and the volume of the linoleate-binding pocket rather than substrate orientation. A single model for positional specificity, that has proved to be inappropriate for arachidonate-binding to mammalian 5-, 12- and 15-lipoxygenases, would appear to be true also for linoleate-binding to plant 9- and 13-lipoxygenases.

Molecular and functional characterization of a rose lipoxygenase cDNA related to flower senescence

A cDNA encoding lipoxygenase, Rlox1, was isolated from a cDNA library of senescing rose petals using tomato lipoxygenase cDNA fragments as probes. Characterization of the Rlox1 protein expressed in Echerichia coli revealed that the Rlox1 protein was a soluble lipoxygenase with an unusual optimal pH in the acidic region (pH 4.5-5.0). Northern blot analysis showed that the transcript of the Rlox1 gene was dramatically increased in response to senescence of rose petals. Treatment of rose flowers with ethylene also elevated the mRNA of the Rlox1 gene. These results suggest that the Rlox1 lipoxygenase is involved in senescence of rose flowers.

A leaf lipoxygenase of potato induced specifically by pathogen infection

Lipoxygenase (LOX) activity has been identified consistently during pathogen-induced defense responses. Here we report the involvement of a specific leaf LOX gene of potato (Solanum tuberosum), designated POTLX-3 (GenBank/EMBL accession no. U60202), in defense responses against pathogens. The sequence of POTLX-3 does not match any other LOX genes of potato and has the greatest match to a tobacco LOX gene that contributes to a resistance mechanism against Phytophthora parasitica var nicotianae. POTLX-3 transcript accumulation was not detected in untreated, healthy potato organs or in wounded mature leaves. POTLX-3 mRNA accumulation was induced in potato leaves treated with ethylene or methyl jasmonate or infected with either virulent or avirulent strains of Phytophthora infestans, the causal agent of late blight. During the resistance response, POTLX-3 was induced within 6 hours, increased steadily through 24 hours, and its mRNA continued to accumulate for a week after inoculation. In contrast, when a plant was susceptible to P. infestans, induction of mRNA accumulation in response to inoculation was inconsistent and delayed. LOX activity assayed during an incompatible interaction in leaves peaked 3 days earlier than during a compatible interaction. POTLX-3 mRNA accumulation also was induced during hypersensitive response development caused by the incompatible pathogen Pseudomonas syringae pv phaseolicola. Our results show that POTLX-3 may be involved specifically in defense responses against pathogen infection.

The pi-helix translates structure into function

A search for the occurrence of the rare pi-helix was performed with Iditis from the Oxford Molecular Group upon the Protein Data Bank. In 8 of the 10 confirmed crystal structures that harbor the pi-helix, its unique conformation has been linked directly to the formation or stabilization of a specific binding site within the protein. In the discussion to follow, the role for each of these eight pi-helices will be addressed in regard to protein function. It is clear upon closer examination that the conformation of the pi-helix has evolved to provide unique structural features within a variety of proteins.

Involvement of cysteine residues and domain interactions in the reversible unfolding of lipoxygenase-1

Urea-induced unfolding of lipoxygenase-1 (LOX1) at pH 7.0 was followed by enzyme activity, spectroscopic measurements, and limited proteolysis experiments. Complete unfolding of LOX1 in 9 M urea in the presence of thiol reducing or thiol modifying reagents was observed. The aggregation and oxidative reactions prevented the reversible unfolding of the molecule. The loss of enzyme activity was much earlier than the structural loss of the molecule during the course of unfolding, with the midpoint concentrations being 4.5 and 7.0 M for activity and spectroscopic measurements, respectively. The equilibrium unfolding transition could be adequately fitted to a three-state, two-step model (N left arrow over right arrow I left arrow over right arrow U) and the intermediate fraction was maximally populated at 6.3 M urea. The free energy change (DeltaG(H(2)O)) for the unfolding of native (N) to intermediate (I) was 14.2 +/- 0.28 kcal/mol and for the intermediate to the unfolded state (U) was 11.9 +/- 0.12 kcal/mol. The ANS binding measurements as a function of urea concentration indicated that the maximum binding of ANS was in 6.3 M urea due to the exposure of hydrophobic groups; this intermediate showed significant amount of tertiary structure and retained nearly 60% of secondary structure. The limited proteolysis measurements showed that the initiation of unfolding was from the C-terminal domain. Thus, the stable intermediate observed could be the C-terminal domain unfolded with exposed hydrophobic domain-domain interface. Limited proteolysis experiments during refolding process suggested that the intermediate refolded prior to completely unfolded LOX1. These results confirmed the role of cysteine residues and domain-domain interactions in the reversible unfolding of LOX1. This is the first report of the reversible unfolding of a very large monomeric, multi-domain protein, which also has a prosthetic group.

Structure and mechanism of lipoxygenases

In mammals, lipoxygenases catalyze the formation of hydroperoxides as the first step in the biosynthesis of several inflammatory mediators. The substrate of this reaction, arachidonic acid, is the key precursor of two families of potent physiological effectors. It is the branch point between two central pathways: one, involving the enzyme cyclooxygenase, leads to the synthesis of prostaglandins and thromboxanes; the other, involving lipoxygenases, leads to the synthesis of leukotrienes and lipoxins, compounds that regulate important cellular responses in inflammation and immunity. While aspirin and other non-steroidal anti-inflammatory compounds are potent inhibitors of cyclooxygenase, no effective pharmacological inhibitor of lipoxygenase is presently available. Lipoxygenases are large non-heme, iron-containing enzymes that use molecular oxygen for the diooxygenation of arachidonic acid to form hydroperoxides, the first step in the biosynthetic pathways leading to leukotrienes and lipoxins. Because of the importance of these compounds, lipoxygenases have been the subject of extensive study: from detailed kinetic measurements to cloning, expression, and site-directed mutagenesis. The sequences of over 50 lipoxygenases have been reported. In addition, the structure of soybean lipoxygenase-1, determined by X-ray diffraction methods, has recently been reported. The structure revealed that the 839 amino acids in the protein are organized in two domains: a beta-sheet N-terminal domain and a large, mostly helical C-terminal domain. The iron is present in the C-terminal domain facing two internal cavities that are probably the conduits through which the fatty acid and molecular oxygen gain access to the metal. Models of the mammalian lipoxygenases based on the soybean structure provide clues about the structural determinants of the positional specificity of the enzyme, and can be used as targets for the design of more effective inhibitors.

Purification and molecular cloning of an 8R-lipoxygenase from the coral Plexaura homomalla reveal the related primary structures of R- and S-lipoxygenases

Lipoxygenases that form S configuration fatty acid hydroperoxides have been purified or cloned from plant and mammalian sources. Our objectives were to characterize one of the lipoxygenases with R stereospecificity, many of which are described in marine and freshwater invertebrates. Characterization of the primary structure of an R-specific enzyme should help provide a new perspective to consider the enzyme-substrate interactions that are the basis of the specificity of all lipoxygenases. We purified an 8R-lipoxygenase of the prostaglandin-containing coral Plexaura homomalla by cation and anion exchange chromatography. This yielded a colorless enzyme preparation, a band of approximately 100 kDa on SDS-polyacrylamide gel electrophoresis, and turnover numbers of 4000 min-1 of 8R-lipoxygenase activity in peak chromatographic fractions. The full-length cDNA was cloned by PCR using peptide sequence from the purified protein and by 5'- and 3'-rapid amplification of cDNA ends. The cDNA encodes a polypeptide of 715 amino acids, including over 70 amino acids identified by peptide microsequencing. A peptide presequence of 52 amino acids is cleaved to give the mature protein of 76 kDa; the difference from the estimated size by SDS-PAGE implies a post-translational modification of the P. homomalla enzyme. All of the iron-binding histidines of S-lipoxygenases are conserved in the 8R-lipoxygenase. However, the C-terminal amino acid is a threonine, as opposed to the isoleucine that provides the carboxylate ligand to the iron in all known S-lipoxygenases. These results establish that the 8R-lipoxygenase is related in primary structure to the S-lipoxygenases. A model of the basis of R and S stereospecificity is described.

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.

Genomic and cDNA cloning of a novel mouse lipoxygenase gene

A novel 12- and 15-lipoxygenase related gene was isolated from a mouse strain 129 genomic phage library in a screen with a human 15-lipoxygenase cDNA probe. The complete genomic sequence revealed 14 exons and 13 introns covering 7.3 kb of DNA. The splice junctions were verified from the cDNA sequences of a series of overlapping RT-PCR products. This novel mouse lipoxygenase gene was found to contain an open reading frame encoding 662 amino acids. The cDNA sequence is 68% identical to the mouse leukocyte type 12-lipoxygenase and 65% identical to the mouse platelet type 12-lipoxygenase cDNA. Nucleotide identities to the human 15-lipoxygenase cDNA and the human platelet type 12-lipoxygenase cDNA are 70% and 67%, respectively. The deduced amino acid sequence is 60% identical to the mouse platelet and leukocyte type 12-lipoxygenase sequences and the human 15- and 12-lipoxygenase sequences. This novel mouse lipoxygenase gene was found to be transcribed predominantly in epidermal tissue and named Aloxe.

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).

Studies on linoleic acid 8R-dioxygenase and hydroperoxide isomerase of the fungus Gaeumannomyces graminis

Linoleic acid is sequentially converted to 7S,8S-dihydroxy-9Z,12Z-octadecadienoic acid by the 8R-dioxygenase and hydroperoxide isomerase of the fungus Gaeumannomyces graminis, which is a common pathogen of wheat. The objective of this study was to separate and characterize the two enzyme activities. The isomerase activity was found mainly in the microsomal fraction of the mycelia and the 8R-dioxygenase in the cytosol. The 8R-dioxygenase could be partially purified by ammonium sulfate precipitation, gel filtration, ion exchange chromatography or isoelectric focusing. The 8R-dioxygenase was unstable during purification, but it could be stabilized by glutathione, glutathione peroxidase and ethylenediaminetetraacetic acid. Several protease inhibitors reduced the enzyme activity. Gel filtration with Sephacryl S-300 showed that most 8R-dioxygenase activity was eluted with the front with little retention. Isoelectric focusing in the presence of ethylene glycol (20%) indicated an isoelectric point of pl 6.1-6.3. The enzyme was retained on strong anion exchange columns at pH 7.4 and could be eluted with 0.3-0.5 M NaCl. Incubation of the enzyme with 0.1 mM linoleic acid led to partial inactivation, which may indicate product inhibition. Paracetamol and the lipoxygenase inhibitor ICI 230,487 at 30 microM inhibited the 8R-dioxygenase by 44 and 58%, respectively. 8R-hydroperoxy-9Z,12Z-octadecadienoic acid was isolated from incubations of linoleic acid with the partially purified enzyme or with the cytosol in the presence of p-hydroxymercuribenzoate. The hydroperoxide was rapidly converted by the hydroperoxide isomerase in the microsomal fractions to 7S,8S-dihydroxy-9Z,12Z-octadecadienoic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Molecular basis of a null mutation in soybean lipoxygenase 2: substitution of glutamine for an iron-ligand histidine

We have investigated the nucleotide sequence and expression of lox2, a mutant form of the gene encoding lipoxygenase 2, an enzyme responsible for unpleasant flavors in soybean [Glycine max (L) Merr.] seeds. Although lox2 transcripts accumulate normally, there are no detectable transcripts for lipoxygenase 1 or 3 in mutant lines that display similar phenotypes characterized by the lack of corresponding lipoxygenase activity and protein in mature seeds. The enzymatically inactive lox2 gene product is readily detectable in mid-maturation-stage seeds but is apparently unstable, since it is absent from mature seed. The protein sequence deduced from the cDNA and genomic DNA sequences of lox2 differs from that of the wild-type gene, Lox2, in the substitution of glutamine for His-532. It is known that His-504 in soybean lipoxygenase 1, which corresponds to His-532 in lipoxygenase 2, is one of the iron-binding ligands essential for lipoxygenase activity. Here we present evidence that the missense mutation substituting Gln for His-532 results in the loss of lipoxygenase 2 from mature soybean seeds.

BW A4C and other hydroxamic acids are potent inhibitors of linoleic acid 8R-dioxygenase of the fungus Gaeumannomyces graminis

Linoleic acid is converted to 8R-hydroperoxylinoleic acid by the soluble 8R-dioxygenase of the fungus Gaeumannomyces graminis. Effects of different lipoxygenase inhibitors on the 8R-dioxygenase were evaluated. Three hydroxamic acid derivatives were investigated. BW A4C (N-(3-phenoxycinnamyl)acetohydroxamic acid) was the most potent with an IC50 of 0.2 microM, followed by zileuton (3-10 microM) and linoleate-hydroxamic acid (0.02 mM). Two other lipoxygenase inhibitors, nordihydroguaiaretic acid and eicosatetraynoic acid, were less potent (IC50 0.09 and 0.15 mM, respectively). The 8R-dioxygenase was also strongly inhibited by commonly used buffer additives, dithiothreitol, beta-mercaptoethanol and phenylmethanesulfonyl fluoride. G. graminis also contains a hydroperoxide isomerase, which converts 8R-hydroperoxylinoleic acid to 7S,8S-dihydroxylinoleic acid. Ammonium sulphate precipitation and gel filtration indicated that the dioxygenase and the hydroperoxide isomerase activities could be separated.

The primary structure of a lipoxygenase from the shoots of etiolated lentil seedlings derived from its cDNA

Screening of a cDNA library constructed from the shoots of etiolated lentil seedlings resulted in finding a 2778 bp cDNA sequence, containing an open reading frame coding for a lipoxygenase of 866 amino acid residues. This lipoxygenase appears to be a novel type of vegetative lipoxygenase, different from the seed lipoxygenases of other leguminosae (complete homology < or = 72%).

Characterization of the non-heme iron center of human 5-lipoxygenase by electron paramagnetic resonance, fluorescence, and ultraviolet-visible spectroscopy: redox cycling between ferrous and ferric states

Purified human 5-lipoxygenase, a non-heme iron containing enzyme, has been characterized by electron paramagnetic resonance, (EPR), ultraviolet (UV)-visible and fluorescence spectroscopy. As isolated, the enzyme is largely in the ferrous state and shows a weak X-band EPR signal extending from 0 to 700 G at 15 K, tentatively ascribed to integer spin Fe(II). Titration of the protein with 13-HPOD (13-hydroperoxyoctadecadienoic acid) generates a strong multicomponent EPR signal in the g' approximately 6 region, a yellow color associated with an increased absorption between 310 and 450 nm (epsilon 330nm = 2400 M-1 cm-1), and a 17% decrease in the intrinsic protein fluorescence. The multiple component nature of the g' approximately 6 signal indicates that the metal center in its oxidized state exists in more than one but related forms. The g' approximately 6 EPR signal and the yellow color reach a maximum when approximately 1 mol of 13-HPOD is added/mol of iron; the resultant EPR spectrum accounts quantitatively for all of the iron in the protein with a signal at g' = 4.3 representing less than 3% of the total iron in the majority of samples. Addition of a hydroxyurea reducing agent abolished the g' approximately 6 signal and yellow color of the protein and also reversed the decrease in fluorescence caused by the oxidant 13-HPOD. The results indicate that the g' approximately 6 EPR signal, the yellow color, and the decreased fluorescence are associated with the formation of the Fe(III) form of the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

The three-dimensional structure of an arachidonic acid 15-lipoxygenase

In mammals, the hydroperoxidation of arachidonic acid by lipoxygenases leads to the formation of leukotrienes and lipoxins, compounds that mediate inflammatory responses. Lipoxygenases are dioxygenases that contain a nonheme iron and are present in many animal cells. Soybean lipoxygenase-1 is a single-chain, 839-residue protein closely related to mammalian lipoxygenases. The structure of soybean lipoxygenase-1 solved to 2.6 angstrom resolution shows that the enzyme has two domains: a 146-residue beta barrel and a 693-residue helical bundle. The iron atom is in the center of the larger domain and is coordinated by three histidines and the COO- of the carboxyl terminus. The coordination geometry is nonregular and appears to be a distorted octahedron in which two adjacent positions are not occupied by ligands. Two cavities, in the shapes of a bent cylinder and a frustum, connect the unoccupied positions to the surface of the enzyme. The iron, with two adjacent and unoccupied positions, is poised to interact with the 1,4-diene system of the substrate and with molecular oxygen during catalysis.

The characterization of 5 histidine-serine mutants of human 5-lipoxygenase

The physical and catalytic properties of 5 histidine-serine mutants of human 5-lipoxygenase (5-LO) have been characterized. The mutants HS363, HS391 and HS400 have activities, pH optima and stabilities similar to those of the wild type enzyme. The iron content of each of these mutants is 0.30-0.53 mol Fe/mol 5-LO which is within the range observed for the wild type enzyme. HS368 contains iron (0.15 and 0.43 mol Fe/mol 5-LO in 2 preparations) but has no detectable oxygenase, leukotriene A4 synthase or anaerobic arachidonate-dependent hydroperoxidase activities. HS368 does have significant reducing agent-dependent hydroperoxidase activity suggesting that His-368 may not be an iron ligand but rather may be involved in interactions with arachidonic acid or the formation of the arachidonyl radical intermediate. HS373 contains no iron and has no detectable activities.

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.