Superoxide Dismutase from the Silkworm,Bombyx mori: Sequence, Distribution, and Overexpression

In silico identification and expression analysis of superoxide dismutases in Tenebrio molitor

BACKGROUND

Insects encounter various environmental stresses, in response to which they generate reactive oxygen species (ROS). Superoxide dismutase (SOD) is an antioxidant metalloenzyme that scavenges superoxide radicals to prevent oxidative damage.

OBJECTIVE

To investigate expressions of SODs under oxidative stress in Tenebrio molitor.

METHODS

Here, we investigated the transcriptional expression of SODs by pesticide and heavy metals in Tenebrio moltior. First, we searched an RNA-Seq database for T. molitor SOD (TmSOD) genes and identified two SOD isoforms (TmSOD1-iso1 and iso2). We examined their activities under developmental stage, tissue-specific, and various types (pesticide and heavy metal) of oxidative stress by using qPCR.

RESULTS

Our results revealed two novel forms of TmSODs. These TmSODs had a copper/zinc superoxide dismutase domain, active site, Cu2+ binding site, Zn2+ binding site, E-class dimer interface, and P-class dimer interface. TmSODs (TmSOD1-iso1 and iso2) were expressed in diverse developmental phases and tissues. Pesticides and heavy metals caused an upregulation of these TmSODs.

CONCLUSION

Our findings suggest that the two TmSODs have different functions in T. molitor, providing insights into the detoxification ability of T. molitor.

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.

Four alternative splicing transcripts of intracellular copper/zinc superoxide dismutase 1 in Oxya chinensis

In this study, we obtained four alternative splicing transcripts of intracellular copper/zinc superoxide dismutase 1 (icCuZnSOD1) in Oxya chinensis. OcicCuZnSOD1a has all common characteristics of CuZnSOD family and is a canonical CuZnSOD. OcicCuZnSOD1b is missing a Zn binding site. OcicCuZnSOD1c lacks Zn ion and is a Cu-only SOD. OcicCuZnSOD1d is missing a CuZnSOD conserved sequence and lacks the E-loop, a conserved disulfide bond, and an active site arginine. OcicCuZnSOD1a was the most heat-resistant and OcicCuZnSOD1c was the most unstable at high temperatures above 55 °C. They were stable at a wide pH range, especially in alkaline conditions. The four variants expressed at the throughout developmental stages and had various tissue expression patterns. OcicCuZnSOD1a and OcicCuZnSOD1d were significantly induced by 8.79 mM CuCl₂ and OcicCuZnSOD1b was significantly up-regulated by 14.67 mM CuCl₂. OcicCuZnSOD1a was significantly inhibited by 19.13 mM ZnSO₄ while OcicCuZnSOD1d were significantly induced by 22.61 mM ZnSO₄. Disc diffusion assay showed that the four isoforms of OcicCuZnSOD1 made the killing zones smaller surrounding the CdCl₂-soaked filter discs. However, the reduction ratios of OcicCuZnSOD1a were the highest. These results implied that the four transcripts played roles in defense against CdCl₂-induced oxidative stress while OcicCuZnSOD1a had stronger antioxidant capacity.

Site-directed mutagenesis (P61G) of copper, zinc superoxide dismutase enhances its kinetic properties and tolerance to inactivation by H2O2

Superoxide dismutases (SODs) protect the cells by catalyzing the dismutation of harmful superoxide radicals (O₂^•-) into molecular oxygen (O₂) and hydrogen peroxide (H₂O₂). Here, a Cu, Zn SOD (WT) from a high altitude plant (Potentilla atrosanguinea) was engineered by substituting a conserved residue proline to glycine at position 61 (P61G). The computational analysis showed higher structural flexibility and clusters in P61G than WT. The P61G exhibited moderately higher catalytic efficiency (K_m = 0.029 μM, V_max = 1488) than WT protein (K_m = 0.038 μM, V_max = 1290.11). P61G showed higher thermostability as revealed from residual activity (72.25% for P61G than 59.31% for WT after heating at 80 °C for 60 min), differential calorimetry scanning and CD-spectroscopic analysis. Interestingly, the P61G mutation also resulted in enhanced tolerance to H₂O₂ inactivation than WT protein. The finding on enhancing the biophysico-chemical properties by mutating conserved residue could stand as an example to engineer other enzymes. Also, the reported mutant can be exploited in food and pharmaceutical industries.

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.

Molecular cloning, expression, and characterization of BmSOD3 in silkworm (Bombyx mori)

Superoxide dismutases (SODs) play an essential role in eliminating excess reactive oxygen species and maintaining the redox balance of the immune system. To study the function of BmSOD3 in silkworm, 543-bp full-length complementary DNA-encoding BmSOD3 was cloned from silkworm. The BmSOD3 amino acids were compared to their homologs, and several highly conserved regions were analyzed. We also carried out phylogenetic analyses of the SOD gene. Our results showed that the BmSOD3 gene belonged with the ecCu/Zn SOD gene. The BmSOD3 gene was transformed into the pET28a vector for functional expression in Escherichia coli. The sodium salt-polyacrylamide gel electrophoresis results showed that the molecular weight of recombinant BmSOD3 was about 22 kDa. The recombinant protein BmSOD3 was purified to detect its properties. After purification analyses, the enzyme activity showed Cu/Zn SOD activity, and the specific activity of the purified enzyme was 0.51 U/mg. The BmSOD3 transcripts showed tissue-specific expression in the midgut and malpighian tubule. The immune microarray data for BmSOD3 showed an expression signal that had a strong response to the induction of four pathogens (Bacillus bombyseptieus, Beauveria bassiana, E. coli, and nuclear polyhedrosis virus), particularly after infection for 24 h, which indicates that the BmSOD3 gene plays a key role in response to bacterial, fungal, and viral invasion. The fusion protein also showed antibacterial activity against E. coli in vitro. Thus, the fusion protein BmSOD3 exhibits antibacterial activity and may be used in production to combat diseases caused by bacteria in silkworm.

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.

A second intracellular copper/zinc superoxide dismutase and a manganese superoxide dismutase in Oxya chinensis: Molecular and biochemical characteristics and roles in chlorpyrifos stress

A second intracellular copper/zinc superoxide dismutase (icCuZnSOD2) and manganese SOD (MnSOD) were cloned and characterized in Oxya chinensis. The open reading frame (ORF) of OcicCuZnSOD2 and OcMnSOD are 462 and 672 bp encoding 153 and 223 amino acids, respectively. OcicCuZnSOD2 contains two signature sequences, one potential N-glycosylation site, and seven copper/zinc binding sites. OcMnSOD includes a mitochondria targeting sequence of 7 amino acids at N-terminal, one signature sequence, two N-glycosylation sites, and four manganese binding sites. The secondary structure and homology model of OcicCuZnSOD2 include nine β sheets, two Greek-key motifs, and one electrostatic loop. OcMnSOD contains nine α-helices and three β-sheets. Phylogenetic analysis shows that OcMnSOD is evolutionarily conserved while OcicCuZnSOD2 may be gene duplication and is paralogous to OcicCuZnSOD1. OcMnSOD expressed widely in all tissues and developmental stages. OcicCuZnSOD2 showed testis-specific expression and expressed highest in the 5th-instar nymph and the adult. The optimum temperatures and pH values of the recombinant OcicCuZnSOD2 and OcMnSOD were 40 °C and 8.0. They were stable at 25-55 °C and at pH 5.0-12.0 and pH 6.0-12.0, respectively. The activity and mRNA expression of each OcSOD were assayed after chlorpyrifos treatments. Total SOD and CuZnSOD activities first increased then declined under chlorpyrifos stress. Chlorpyrifos induced the mRNA expression and activity of OcMnSOD as a dose-dependent manner and inhibited OcicCuZnSOD2 transcription. The role of each OcSOD gene in chlorpyrifos stress was investigated using RNAi and disc diffusion assay with Escherichia coli overexpressing OcSOD proteins. Silencing of OcMnSOD significantly increased ROS content in chlorpyrifos-exposed grasshoppers. Disc diffusion assay showed that the plates with E. coli overexpressing OcMnSOD had the smaller inhibition zones around the chlorpyrifos-soaked filter discs. These results implied that OcMnSOD played a significant role in defense chlorpyrifos-induced oxidative stress.

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.

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.

Involvement of superoxide dismutase in oxidative stress in the oriental fruit fly, Bactrocera dorsalis: molecular cloning and expression profiles

BACKGROUND

Bactrocera dorsalis, one of the most economically important fruit fly pests in East Asia, is well adapted to various environmental conditions. Pesticides, pathogens and other stresses can cause oxidative damage in most organisms. The superoxide dismutase (SOD) family contains some of the most important enzymes in the antioxidant protection system of the fruit fly and other organisms.

RESULTS

Four full-length cDNA sequences encoding one MnSOD (BdSOD2-1) and three Cu-ZnSODs (BdSOD1-1, BdSOD1-2 and BdSOD1-3) were cloned. The expression profiles of these four genes under different stresses showed them to be involved in response to detrimental conditions including heavy metals, pesticides, extreme temperatures and lipopolysaccharide (LPS) stresses. More specifically, the expression levels of these genes were found to be depressed in the presence of copper, zinc and manganese. The expression of all four SOD genes increased upon exposure to lead, cadmium, low temperature (0 °C) and LPS stresses. Only BdSOD1-3 transcription increased significantly at high temperature (40 °C) exposure. The expressions levels of BdSOD1-2 and BdSOD1-3 increased significantly in the presence of β-cypermethrin and malathion, but only the expression of BdSOD2-1 increased in the presence of avermectin treatment.

CONCLUSION

These different expression profiles suggest that the four BdSODs play different roles and respond to different oxidative stresses in B. dorsalis. Some BdSODs undergo specific reaction in the response to specific oxidative stresses.

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%).

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.

Immunity promotion and proteomic identification in mice upon exposure to manganese superoxide dismutase expressed in silkworm larvae

With manganese superoxide dismutase (SOD) expressed in silkworm larvae, Bomby mori L, we investigated the effects of silkworm larvae powder containing SOD on the immune system of mouse and employed a proteomics approach to examine this phenomenon. Our data on the effects of continuous treatment with SOD-containing silkworm larvae powder showed that the ConA-stimulated splenocyte proliferation of all three treated groups was higher than that of the control. The results of PFC assay also revealed that antibody production was higher in all three treated groups than controlled mice. We investigated the phagocytosis of mouse macrophages. The SOD treatment led to a dose-dependent increase of phagocytic activity. We identified six proteins that related to immunity of mice. The data showed all these six matched proteins related immunity presented the increase of expression level in plasma of mouse administrated with silkworm powder including SOD compared to that of control. These findings demonstrate that administration of silkworm larvae powder containing SOD results in enhancement of immunity activities in the mouse. The results also suggested that the SOD expressed in silkworm maybe have potential application in medicine.

The Molecular Mechanism of the Termination of Insect Diapause, Part 1: A Timer Protein, TIME-EA4, in the Diapause Eggs of the Silkworm Bombyx mori is a Metallo-Glycoprotein

TIME-EA4 is an ATPase that measures time intervals, functioning as a diapause duration clock in diapause eggs of the silkworm, Bombyx mori. Characterization of the primary and higher structures of the TIME-EA4 would be desirable to clarify the mechanism by which the protein measures the time intervals. In our current studies, the whole sequence of TIME-EA4 has been established as that of a metallo-glycoprotein by combinational means involving peptide sequence analysis, nano-HPLC-ESI-Q-TOF-MS and MS/MS, and cDNA dictation. The amino acid sequence of TIME-EA4 showed 46-55 % homology with the reported proteins of the Cu,Zn-SOD (superoxide dismutase) family; in particular, the SOD active site (core domain) includes metal-binding amino acid ligands and a disulfide bond, and these structures are completely identical in Bombyx SOD, bovine SOD, and TIME-EA4 proteins. We found, however, that TIME-EA4 contains one more copper ion than other SODs, as was proven under neutral nondenaturing conditions. ESI mass spectrometry revealed that the timer function was not in the SOD core domain. In addition, TIME-EA4 has an attached sugar chain, which is indispensable to its functioning as a timer protein.

Cloning and expression of manganese superoxide dismutase of the silkworm, Bombyx mori by Bac-to-Bac/BmNPV Baculovirus expression system

Superoxide dismutase (SODs) are metalloenzymes that catalyze the dismutation of the superoxide anion to molecular oxygen and hydrogen peroxide and, thus, form a crucial part of the cellular antioxidant defense mechanism. In this paper, we used the total fat body RNA of silkworm, Bombyx mori L. to clone and sequence a 648-bp Mn-SOD cDNA fragment through RT-PCR. Furthermore, a newly established Bac-to-Bac/BmNPV Baculovirus expression system was used to overexpress the recombinant Mn-SOD enzyme in silkworm larvae. The hemolymph was collected from the infected larvae 96 h post-infection and subjected to a 12 % SDS-PAGE and Western blotting. A 18.0-kDa protein was visualized after rBacmid/BmNPV/SOD infection. The SOD enzyme activity was determined with a tetrazolium salt for detection of superoxide radicals generated by xanthine and xanthine oxidase and its peak appeared in 96 h post-infection with 2.7 times of the control larvae. The availability of large quantities of SOD that the silkworm provides should greatly facilitate the future research and testing of this protein for potential application in medicine.

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

Superoxide dismutase (SOD) is responsible for the removal of superoxide anion from living organisms. In this study, cDNA encoding the manganese-containing SOD (MnSOD) from the silkworm, Bombyx mori, was isolated by reverse transcriptase-polymerase chain reaction and sequenced. The deduced amino acid sequence of the MnSOD revealed 62% identity to that of the Drosophila melanogaster; both were close to each other in a phylogenetic tree. The MnSOD was overproduced in Escherichia coli and purified. The internal structure of the recombinant MnSOD was confirmed by peptide mass fingerprinting method. The recombinant MnSOD facilitating the reduction reaction of superoxide anion retained 75% of its original activity after incubation at pH 4-11 for 24 h at 4 degrees C. Its activity was never affected by incubation at pH 7 for 30 min below 50 degrees C.