Molecular and biochemical characterization of manganese-containing superoxide dismutase from the silkworm, Bombyx mori

The superoxide dismutase (SOD) genes family mediates the response of Nilaparvata lugens to jinggangmycin and sugar

Introduction: Brown planthopper (BPH), Nilaparvata lugens Stål (Hemiptera: Delphacidae), is a major rice pest causing significant damage to rice throughout the world. Intensive pesticide usage often causes resistance in these seasonal pests, mainly through the modulation of antioxidant machinery. The superoxide dismutase (SOD) gene family is known for regulating BPH response to pesticides. Methods: In the present study, we identified eight NlSOD genes from the NCBI using the BLASTP program. The bioinformatics analysis includes a phylogenetic tree, conserved domain, motifs, gene ontology (GO) analysis, Kyoto encyclopedia of genes and genomes (KEGG) pathways, and protein-protein interaction, highlighting the distinctive functional elements of NlSOD genes. Results and discussion: Additionally, the NlSOD genes showed expression in all developmental stages of BPH. Under three sugars (glucose, sucrose, and trehalose) treatment, the respective upregulation of NlSOD8, NlSOD6, and NlSOD2 was noted. The NlSOD1 induced significantly under jinggamycin (JGM) deduced its potential as a key regulator of BPH response to the pesticide. Our study has provided detailed knowledge of the NlSOD gene family in-silico analysis and the defensive response to insecticide and high sugar of BPH. We hope the results of this research will help to shed light on the resistance of BPH towards insecticide toxicity and high sugar and help to control it more efficiently.

Characterization of a novel superoxide dismutase in Nilaparvata lugens

The brown planthopper (Nilaparvata lugens) is a major agricultural pest of rice crops. Analysis of the enzymes produced by N. lugens is important to develop pest-control methods. Superoxide dismutase (SOD) is a detoxification enzyme that catalyzes the conversion of superoxide anions (reactive oxygen species) into oxygen and hydrogen peroxide. As there have been no reports on SOD in N. lugens, in this study, we characterized a new SOD in the brown planthopper, nlSOD1. Amino acid sequence and phylogenetic analyses revealed that nlSOD1 is a member of the Cu/Zn-SOD family. Recombinant nlSOD1, when overexpressed in Escherichia coli, catalyzes the dismutation of superoxide radicals into molecular O₂ and H₂ O₂ . Exposure to various insecticides induced nlSOD1 messenger RNA expression. These results indicate that nlSOD1 may contribute to the insecticide resistance of N. lugens. The findings of this study may assist in the development of novel methods to control the population of N. lugens.

Characterization of Heat Shock Protein 60 as an Interacting Partner of Superoxide Dismutase 2 in the Silkworm, Bombyx mori, and Its Response to the Molting Hormone, 20-Hydroxyecdysone

Oxidative stress promotes pupation in some holometabolous insects. The levels of superoxide, a reactive oxygen species (ROS), are increased and superoxide dismutase 1 (BmSod1) and superoxide dismutase 2 (BmSod2) are decreased during metamorphic events in silkworm (Bombyx mori). These observations strongly suggest that pupation is initiated by oxidative stress via the down-regulation of BmSod1 and BmSod2. However, the molecular mechanisms underlying ROS production during metamorphic events in silkworm remain unknown. To investigate these molecular mechanisms, the peripheral proteins of BmSod1 and BmSod2 were identified and characterized using dry and wet approaches in this study. Based on the results, silkworm heat shock protein 60 (BmHsp60) was identified as an interacting partner of BmSod2, which belongs to the Fe/MnSOD family. Furthermore, the present study results showed that BmHsp60 mRNA expression levels were increased in response to oxidative stress caused by ultraviolet radiation and that BmHsp60 protein levels (but not mRNA levels) were decreased during metamorphic events, which are regulated by the molting hormone 20-hydroxyecdysone. These findings improve our understanding of the mechanisms by which holometabolous insects control ROS during metamorphosis.

Characterization of a Mn-SOD from the desert beetle Microdera punctipennis and its increased resistance to cold stress in E. coli cells

Insects have developed a complex network of enzymatic antioxidant systems for handling reactive oxygen species (ROS) generated during stress. Superoxide dismutases (SODs) play a determinant role in balancing ROS in insect. However, studies devoted to SODs functions in insects under cold stress are limited. In the present study, we attempted to identify and characterize a mitochondrial manganese SOD (mMn-SOD) from the desert beetle Micordera punctipennis (denoted as MpmMn-SOD) and explore its protective effects on bacteria cells under cold stress. MpmMn-SOD is composed of 202 amino acids with conserved domains required for metal ions binding and enzyme activity. RT-qPCR experiments revealed that the expression of MpmMn-SOD was ubiquitous but tissue-specific and was induced by cold stress. An E. coli (BL21) system was applied to study the function of MpmMn-SOD. The MpmMn-SOD gene was cloned into the prokaryotic expression vector pET-32a to generate a recombinant plasmid pET-32a(MpmMn-SOD). After transformation of the plasmid into E. coli BL21, the fusion protein Trx-His-MpmMn-SOD was overexpressed and identified by SDS-PAGE and Western blotting. Antioxidant activity assay showed that the death zones of the transformed bacteria BL21 (pET32a-mMn-SOD) were smaller in diameter than the control bacteria BL21 (pET32a). Survival curves under -4 °C showed that BL21 (pET32a-mMn-SOD) had significant enhanced cold resistance compared to BL21 (pET32a). Its SOD activity under -4 °C had a significant negative correlation (r = - 0.995) with superoxide anion O2 •- content. Accordingly, under cold stress BL21 (pET32a-mMn-SOD) had lower electric conductivity and malondialdehyde (MDA) content than BL21 (pET32a). Taken together, our results showed that cold stress stimulated the expression of MpmMn-SOD in M. punctipennis. The E. coli cells that overexpress MpmMn-SOD increase their resistance to cold stress by scavenging ROS, and mitigate potential cell damage caused by ROS under cold conditions.

Superoxide dismutase down-regulation and the oxidative stress is required to initiate pupation in Bombyx mori

Perhaps, oxidative stress progresses pupation in some Lepidopteran insects; however, the reasons for this remain obscure. In our previous study, we clarified Bombyx mori SOD1 (BmSOD1) and B. mori SOD2 (BmSOD2) proteins respond in common to ultraviolet irradiation (UV) oxidative stress and metamorphosis. This result strongly suggested pupation initiates by oxidative stress and might mediate by down-regulation of expression of BmSOD1 and BmSOD2 proteins. Thus, we examined about these relationships in B. mori in this study. In the microarray data reanalysis, we found the Notch signaling pathways as the common pathways in pupation and UV oxidative stress in B. mori. Also, we showed a molting hormone, 20-hydroxyecdysone, leads not only generation of superoxide but also downregulation of the expression of BmSOD proteins during pupation in B. mori. Our findings can contribute to a deeper understanding of how biological defense systems work against environmental oxidative stress.

A superoxide dismutase (MnSOD) with identification and functional characterization from the freshwater mussel Cristaria plicata

Manganese superoxide dismutase (MnSOD) is a sort of important metalloenzyme that can catalyze ROS in the organisms. In this study, MnSOD cDNA of C. plicata, designated as CpMnSOD (accession no. MK465057), was cloned from hemocytes. The full-length cDNA of MnSOD was 1096 bp with a 672 bp open reading frame encoding 223 amino acids. The deduced amino acid sequence contained a mitochondrial-targeting sequence (MTS) of 18 amino acids in the N-terminus, and four conserved amino acids for manganese binding (H⁴⁹, H⁹⁷, D¹⁸², H¹⁸⁶). CpMnSOD showed a high level (65-73%) of sequence similarity to MnSODs from other species. The results of Real-time quantitative PCR revealed that CpMnSOD mRNA constitutively expressed in tissues. The highest expression level was in hepatopancreas, followed by muscle, mantle and gill, and the lowest expression level was in hemocytes. After microcystin challenge, the expression levels of CpMnSOD mRNA were up-regulated in hemocytes and hepatopancreas. The cDNA of CpMnSOD was cloned into the plasmid pColdI-ZZ, and the recombinant protein was expressed in Escherichia coli BL21 (DE3). The enzyme stability assay showed that the purified CpMnSOD protein maintained more than 80% enzyme activity at temperature up to 70 °C, at pH 2.0-10.0, and resistant to 8 mol/L urea or 8% SDS.

A manganese superoxide dismutase (MnSOD) from ark shell, Scapharca broughtonii: Molecular characterization, expression and immune activity analysis

Manganese superoxide dismutase (MnSOD) is one of the key members of the antioxidant defense enzyme family, however, data regarding to the immune function of MnSOD in mollusks still remain limited now. In this study, a full-length MnSOD cDNA was identified by rapid amplification of cDNA ends (RACE) method from cDNA library of ark shell Scapharca broughtonii (termed SbMnSOD). The cDNA contained an open reading frame (ORF) of 696 bp which encoded a polypeptide of 232 amino acids, a 5'-UTR with length of 32 bp and a 3'-UTR of 275 bp. Four putative amino acid residues (His-57, His-105, Asp-190 and His-194) responsible for manganese coordination were located in the most highly conserved regions of SbMnSOD and the signature sequence (DVWEHAYY) also existed in SbMnSOD. The deduced amino acid sequence of SbMnSOD shared high homology to MnSOD from other species. All those data revealed that the SbMnSOD was a novel member of the MnSOD family. The mRNA expression profiles of SbMnSOD in tissues of foot, gill, mantle, adductor muscle, hemocytes and hepatopancreas analyzed by quantitative real-time PCR (qRT-PCR) suggested the mRNA transcripts of SbMnSOD distributed in all the examined tissues. Importantly, Vibrio anguillarum challenge resulted in the increased expression of SbMnSOD mRNA with a regular change trend in all examined tissues, indicating SbMnSOD actively participated in the immune response process. What's more, further analysis on the antibacterial activity of the recombinant SbMnSOD showed that the fusion protein could remarkably inhibit growth of both Gram-positive and Gram-negative bacteria. The present results clearly suggested that SbMnSOD was an acute phase protein involved in the immune reaction in S. broughtonii.

Superoxide dismutases, SOD1 and SOD2, play a distinct role in the fat body during pupation in silkworm Bombyx mori

One way that aerobic biological systems counteract the generation of reactive oxygen species (ROS) is with superoxide dismutase proteins SOD1 and SOD2 that metabolize superoxide radicals to molecular oxygen and hydrogen peroxide or scavenge oxygen radicals produced by the extensive oxidation-reduction and electron-transport reactions that occur in mitochondria. We characterized SOD1 and SOD2 of Bombyx mori isolated from the fat body of larvae. Immunological analysis demonstrated the presence of BmSOD1 and BmSOD2 in the silk gland, midgut, fat body, Malpighian tubules, testis and ovary from larvae to adults. We found that BmSOD2 had a unique expression pattern in the fat body through the fifth instar larval developmental stage. The anti-oxidative functions of BmSOD1 and BmSOD2 were assessed by exposing larvae to insecticide rotenone or vasodilator isosorbide dinitrate, which is an ROS generator in BmN4 cells; however, exposure to these compounds had no effect on the expression levels of either BmSOD protein. Next, we investigated the physiological role of BmSOD1 and BmSOD2 under environmental oxidative stress, applied through whole-body UV irradiation and assayed using quantitative RT-PCR, immunoblotting and microarray analysis. The mRNA expression level of both BmSOD1 and BmSOD2 was markedly increased but protein expression level was increased only slightly. To examine the differences in mRNA and protein level due to UV irradiation intensity, we performed microarray analysis. Gene set enrichment analysis revealed that genes in the insulin signaling pathway and PPAR signaling pathway were significantly up-regulated after 6 and 12 hours of UV irradiation. Taken together, the activities of BmSOD1 and BmSOD2 may be related to the response to UV irradiation stress in B. mori. These results suggest that BmSOD1 and BmSOD2 modulate environmental oxidative stress in the cell and have a specific role in fat body of B. mori during pupation.

Parasitization by Scleroderma guani influences expression of superoxide dismutase genes in Tenebrio molitor

Superoxide dismutase (SOD) is an antioxidant enzyme involved in detoxifying reactive oxygen species. In this study, we identified genes encoding the extracellular and intracellular copper-zinc SODs (ecCuZnSOD and icCuZnSOD) and a manganese SOD (MnSOD) in the yellow mealworm beetle, Tenebrio molitor. The cDNAs for ecCuZnSOD, icCuZnSOD, and MnSOD, respectively, encode 24.55, 15.81, and 23.14 kDa polypeptides, which possess structural features typical of other insect SODs. They showed 20-94% identity to other known SOD sequences from Bombyx mori, Musca domestica, Nasonia vitripennis, Pediculus humanus corporis, and Tribolium castaneum. Expression of these genes was analyzed in selected tissues and developmental stages, and following exposure to Escherichia coli and parasitization by Scleroderma guani. We recorded expression of all three SODs in cuticle, fat body, and hemocytes and in the major developmental stages. Relatively higher expressions were detected in late-instar larvae and pupae, compared to other developmental stages. Transcriptional levels were upregulated following bacterial infection. Analysis of pupae parasitized by S. guani revealed that expression of T. molitor SOD genes was significantly induced following parasitization. We infer that these genes act in immune response and in host-parasitoid interactions.

A manganese superoxide dismutase with potent antioxidant activity identified from Oplegnathus fasciatus: genomic structure and transcriptional characterization

In this study, we describe the identification and characterization of manganese superoxide dismutase, an important antioxidant enzyme acting as the chief reactive oxygen species (ROS) scavenger, from rock bream Oplegnathus fasciatus (Of-mMnSOD) at genomic- and transcriptional-levels as well as the biological activity of recombinant protein. The Of-mMnSOD protein portrayed distinct MnSOD family features including signature motifs, metal association sites and the typical active site topology. It was also predicted to be localized in mitochondrial matrix. The Of-mMnSOD had a quinquepartite genome organization encompassing five exons interrupted by four introns. Comparison of its sequence and gene structure with that of other lineages emphasized its strong conservation among different vertebrates. The Of-mMnSOD was ubiquitously transcribed in different rock bream tissues with higher levels in blood cells and metabolically active tissues. Transcription of Of-mMnSOD was kinetically modulated in response to investigational challenges using mitogens (lipopolysaccharide and poly I:C) and live-pathogens (Edwardsiella tarda and rock bream irido virus) in blood cells and liver tissue. The purified recombinant Of-mMnSOD possessed potential antioxidant capacity and actively survived over a range of pH (7.5-11) and temperature (15-40 °C) conditions. Collectively, findings of this study suggest that Of-mMnSOD combats against oxidative stress and cellular damages induced by mitogen/pathogen-mediated inflammation, by detoxifying harmful ROS (O(2)(●-)) in rock bream.

Annotation and evolution of the antioxidant genes in the silkworm, Bombyx mori

Antioxidant system, which is composed of multiple gene families, plays a major role in reducing oxidative damage and xenobiotic detoxification in all living organisms. We identified 50 silkworm antioxidant genes from nine gene families based on the assembled genome sequence. A comparative analysis of the antioxidant genes of the silkworm with other order insects Anopheles gambiae, Apis mellifera, Drosophila melanogaster, and Tribolium castaneum, was performed. We found that most of the antioxidant gene families are highly conserved but Catalase (CAT) and heme-containing peroxidase (HPX) families were lineage-specifically expanded in the silkworm. The expression patterns of the silkworm antioxidant genes were investigated with the known ESTs, microarray data, and reverse transcription-polymerase chain reaction (RT-PCR). Forty two of the 50 silkworm antioxidant genes were transcribed and most of the transcribed genes showed tissue-specific expression patterns. More than a half of lineage-specifically expanded BmCATs lacked 15 or more than 15 of the 36 heme-binding residues and might lose catalase activities. However, the genes encoding these BmCATs showed almost a ubiquitous tissue expression pattern, indicating that they might have evolved new functions. In addition, the lineage-specifically expanded BmHPXs could function in maintaining cell homeostasis in the process of the synthesis of large amounts of silk proteins because they were predominantly expressed in silk gland of the silkworm. The lineage-specific expansion of antioxidant gene families in the silkworm provides useful information for understanding evolution and functional versatility of antioxidant genes in the silkworm even Lepidopteran insects.

Microarray expression profiling of Spodoptera litura in response to oxidative stress

To examine the expression profile of oxidative stress responsive genes in Spodoptera litura, we constructed a cDNA library from S. litura injected with hydrogen peroxide (H(2)O(2)). Using a microarray chip composed of 2,964 cDNAs, we screened gene expression at 1, 3, 5, 7, and 9 h post H(2)O(2) injection. Data were clustered into 15 groups of genes that behave similarly across each time course. Seventy-three genes were identified as being at least twofold up- or downregulated after treatment with H(2)O(2) in S. litura. We constructed expressed sequence tags (ESTs) for genes that changed at least twofold after treatment with H(2)O(2) . The functional classification of these ESTs based on Gene Ontology showed that the ESTs are rich in genes involved in oxidoreductase activity (5.7%), defense (14.3%), cellular process (22.9%), and development (17.1%).

Molecular cloning, characterization, and the response of manganese superoxide dismutase from the Antarctic bivalve Laternula elliptica to PCB exposure

Manganese superoxide dismutase (leMnSOD) cDNA was cloned from the Antarctic bivalve Laternula elliptica. The full-length cDNA of leMnSOD is 1238 bp in length and contains an open reading frame of 681 bp encoding 226 amino acid residues including a putative mitochondrial targeting peptide of 26 amino acids in the N-terminal region. The calculated molecular mass is 24.8 kDa with an estimated isoelectric point of 6.75. leMnSOD signatures from 185 to 192 (DVWEHAYY) and four conserved amino acids (H52, H11, D185, and H192) responsible for binding manganese were observed. Sequence comparison showed that leMnSOD had high levels of identity with MnSOD from Haliotis discus discus, Mizuhopecten yessoensis, and Crassostrea gigas (68%, 66%, and 59%, respectively). RT-PCR analysis revealed the presence of leMnSOD transcripts in all tissues examined. Quantitative real-time RT-PCR assay indicated that treatment with polychlorinated biphenyls (PCBs) significantly increased leMnSOD mRNA expression in an organ-, time-, and dose-dependent manner. The mRNA expression with exposure to PCBs at 0.1 and 10 ppb reached the highest level at 6 h and then recovered slightly from 6 to 48 h in the gill. In contrast, the expression of leMnSOD mRNA showed a different expression pattern related to PCB concentration in the digestive gland. The mRNA expression at 0.1 ppb PCBs increased up to 12 h and then decreased by 48 h, but increased immediately at 10 ppb PCBs. The leMnSOD was overproduced in Escherichia coli and purified. The recombinant leMnSOD showed maximum activity at pH 9.0, and it retained more than 50% of its original activity after incubation for 30 min at 40 degrees C.

Characterization, molecular modelling and developmental expression of zebrafish manganese superoxide dismutase

A 977 bp cDNA containing an open reading frame encoding 224 amino acid residues of manganese superoxide dismutase was cloned from zebrafish (zMn-SOD). The deduced amino acid sequence showed high identity with the sequences of Mn-SODs from human (85.1%) to nematode (61.6%). The 3-D structure model was superimposed on the relative domains of human Mn-SOD with the root mean square (rms) deviation of 0.0919 A. The recombinant mature zMn-SOD with enzyme activity was purified using His-tag technique. The half-life of the enzyme is approximately 48 min and its thermal inactivation rate constant k(d) is 0.0154 min(-1)at 70 degrees C. The enzyme was active under a broad pH (2.2-11.2) and in the presence of up to 4% SDS. Real-time RT-PCR assay was used to detect the zMn-SOD mRNA expression during the developmental stages following a challenge with paraquat. A high level expression of Mn-SOD mRNA was detected at the cleavage stage, but decreased significantly under paraquat treatment. The results indicated that Mn-SOD plays an important role during embryonic development.

Thioredoxin from the silkworm, Bombyx mori: cDNA sequence, expression, and functional characterization

A thioredoxin (Trx) gene was cloned from the silkworm, Bombyx mori. The B. mori Trx (BmTrx) cDNA contains an open reading frame of 318 bp encoding 106 amino acid residues with a conserved active site (CGPC). Northern blot analysis revealed the presence of BmTrx transcripts in all tissues examined. The cDNA encoding BmTrx was expressed as a 12-kDa polypeptide in baculovirus-infected insect Sf9 cells. The recombinant BmTrx proved to be biologically active, using an insulin reduction assay, and was also able to activate thioredoxin peroxidase from B. mori. When H2O2 or paraquat was injected into the body cavity of B. mori larvae, BmTrx mRNA expression was upregulated in the fat body tissue. In addition, the expression levels of BmTrx mRNA in the fat body were greatly increased when B. mori larvae were exposed to low or high temperatures, or injected with microorganisms. These results suggest that BmTrx possibly protects against oxidative stress caused by extreme temperatures and microbial infection as well as by intracellularly generated reactive oxygen species during metabolism.