Jeong Chan Moon

Heat-shock dependent oligomeric status alters the function of a plant-specific thioredoxin-like protein, AtTDX

We found that Arabidopsis AtTDX, a heat-stable and plant-specific thioredoxin (Trx)-like protein, exhibits multiple functions, acting as a disulfide reductase, foldase chaperone, and holdase chaperone. The activity of AtTDX, which contains 3 tetratricopeptide repeat (TPR) domains and a Trx motif, depends on its oligomeric status. The disulfide reductase and foldase chaperone functions predominate when AtTDX occurs in the low molecular weight (LMW) form, whereas the holdase chaperone function predominates in the high molecular weight (HMW) complexes. Because deletion of the TPR domains results in a significant enhancement of AtTDX disulfide reductase activity and complete loss of the holdase chaperone function, our data suggest that the TPR domains of AtTDX block the active site of Trx and play a critical role in promoting the holdase chaperone function. The oligomerization status of AtTDX is reversibly regulated by heat shock, which causes a transition from LMW to HMW complexes with concomitant functional switching from a disulfide reductase and foldase chaperone to a holdase chaperone. Overexpression of AtTDX in Arabidopsis conferred enhanced heat shock resistance to plants, primarily via its holdase chaperone activity.

Heat-Shock and Redox-Dependent Functional Switching of an h-Type Arabidopsis Thioredoxin from a Disulfide Reductase to a Molecular Chaperone

A large number of thioredoxins (Trxs), small redox proteins, have been identified from all living organisms. However, many of the physiological roles played by these proteins remain to be elucidated. We isolated a high Mr (HMW) form of h-type Trx from the heat-treated cytosolic extracts of Arabidopsis (Arabidopsis thaliana) suspension cells and designated it as AtTrx-h3. Using bacterially expressed recombinant AtTrx-h3, we find that it forms various protein structures ranging from low and oligomeric protein species to HMW complexes. And the AtTrx-h3 performs dual functions, acting as a disulfide reductase and as a molecular chaperone, which are closely associated with its molecular structures. The disulfide reductase function is observed predominantly in the low Mr forms, whereas the chaperone function predominates in the HMW complexes. The multimeric structures of AtTrx-h3 are regulated not only by heat shock but also by redox status. Two active cysteine residues in AtTrx-h3 are required for disulfide reductase activity, but not for chaperone function. AtTrx-h3 confers enhanced heat-shock tolerance in Arabidopsis, primarily through its chaperone function.

Abnormal Chloroplast Development and Growth Inhibition in Rice Thioredoxin m Knock-Down Plants

Plant cells contain several thioredoxin isoforms that are characterized by subcellular localization and substrate specificity. Here, we describe the functional characterization of a rice (Oryza sativa) thioredoxin m isoform (Ostrxm) using a reverse genetics technique. Ostrxm showed green tissue-specific and light-responsive mRNA expression. Ostrxm was localized in chloroplasts of rice mesophyll cells, and the recombinant protein showed dithiothreitol-dependent insulin β-chain reduction activity in vitro. RNA interference (RNAi) of Ostrxm resulted in rice plants with developmental defects, including semidwarfism, pale-green leaves, abnormal chloroplast structure, and reduced carotenoid and chlorophyll content. Ostrxm RNAi plants showed remarkably decreased Fv/Fm values under high irradiance conditions (1,000 μmol m−2 s−1) with delayed recovery. Two-dimensional electrophoresis and matrix-assisted laser-desorption/ionization time-of-flight analysis showed that the levels of several chloroplast proteins critical for photosynthesis and biogenesis were significantly decreased in Ostrxm RNAi plants. Furthermore, 2-Cys peroxiredoxin, a known target of thioredoxin, was present in oxidized forms, and hydrogen peroxide levels were increased in Ostrxm RNAi plants. The pleiotropic effects of Ostrxm RNAi suggest that Ostrxm plays an important role in the redox regulation of chloroplast target proteins involved in diverse physiological functions.

Cowpea bruchid midgut transcriptome response to a soybean cystatin - Costs and benefits of counter-defence

The insect digestive system is the first line of defence protecting cells and tissues of the body from a broad spectrum of toxins and antinutritional factors in its food. To gain insight into the nature and breadth of genes involved in adaptation to dietary challenge, a collection of 20 352 cDNAs was prepared from the midgut tissue of cowpea bruchid larvae (Callosobruchus maculatus) fed on regular diet and diets containing antinutritional compounds. Transcript responses of the larvae to dietary soybean cystatin (scN) were analysed using cDNA microarrays, followed by quantitative real‐time PCR (RT‐PCR) confirmation with selected genes. The midgut transcript profile of insects fed a sustained sublethal scN dose over the larval life was compared with that of insects treated with an acute high dose of scN for 24 h. A total of 1756 scN‐responsive cDNAs was sequenced; these clustered into 967 contigs, of which 653 were singletons. Many contigs (451) did not show homology with known genes, or had homology only with genes of unknown function in a Blast search. The identified differentially regulated sequences encoded proteins presumptively involved in metabolism, structure, development, signalling, defence and stress response. Expression patterns of some scN‐responsive genes were consistent in each larval stage, whereas others exhibited developmental stage‐specificity. Acute (24 h), high level exposure to dietary scN caused altered expression of a set of genes partially overlapping with the transcript profile seen under chronic lower level exposure. Protein and carbohydrate hydrolases were generally up‐regulated by scN whereas structural, defence and stress‐related genes were largely down‐regulated. These results show that insects actively mobilize genomic resources in the alimentary tract to mitigate the impact of a digestive protease inhibitor. The enhanced or restored digestibility that may result is possibly crucial for insect survival, yet may be bought at the cost of weakened response to other stresses.

Functional expression of an insect cathepsin B-like counter-defence protein.

Insects are capable of readjusting their digestive regimes in response to dietary challenge. Cowpea bruchids (Callosobruchus maculatus) strongly induce C. maculatus cathepsin B‐like cysteine protease 1 (CmCatB1) transcripts when fed diet containing a soybean cysteine protease inhibitor soyacystatin N (scN). CmCatB1 shares significant sequence similarity with cathepsin B‐like cysteine proteases. In this study, we isolated another cDNA, namely CmCatB2 that encodes a protein sequence otherwise identical to CmCatB1, but lacking a 70‐amino‐acid internal section. CmCatB1 and CmCatB2 probably resulted from alternate splicing events. Only the CmCatB1 transcript, however, exhibited differential expression in response to dietary scN. Further, this expression was only detectable in larvae, which is the developmental stage associated with food ingestion. The scN‐activated and developmentally regulated CmCatB1 expression pattern suggests it may have a unique function in insect counter‐defence against antinutritional factors. Heterologously expressed recombinant CmCatB1 protein exhibited enzymatic activity in a pH‐dependent manner. Activity of the protein was inhibited by both the cysteine protease inhibitor E‐64 and the cathepsin B‐specific inhibitor CA‐074, verifying its cathepsin B‐like cysteine protease nature. Interestingly, the enzymatic activity was unaffected by the presence of scN. Together, we have provided functional evidence suggesting that CmCatB1 confers inhibitor‐insensitive enzymatic activity to cowpea bruchids, which is crucial for insect survival when challenged by dietary protease inhibitors.

Thioredoxin Reductase Type C (NTRC) Orchestrates Enhanced Thermotolerance to Arabidopsis by Its Redox-Dependent Holdase Chaperone Function

Genevestigator analysis has indicated heat shock induction of transcripts for NADPH-thioredoxin reductase, type C (NTRC) in the light. Here we show overexpression of NTRC in Arabidopsis (NTRC°(E)) resulting in enhanced tolerance to heat shock, whereas NTRC knockout mutant plants (ntrc1) exhibit a temperature sensitive phenotype. To investigate the underlying mechanism of this phenotype, we analyzed the proteins biochemical properties and protein structure. NTRC assembles into homopolymeric structures of varying complexity with functions as a disulfide reductase, a foldase chaperone, and as a holdase chaperone. The multiple functions of NTRC are closely correlated with protein structure. Complexes of higher molecular weight (HMW) showed stronger activity as a holdase chaperone, while low molecular weight (LMW) species exhibited weaker holdase chaperone activity but stronger disulfide reductase and foldase chaperone activities. Heat shock converted LMW proteins into HMW complexes. Mutations of the two active site Cys residues of NTRC into Ser (C217/454S-NTRC) led to a complete inactivation of its disulfide reductase and foldase chaperone functions, but conferred only a slight decrease in its holdase chaperone function. The overexpression of the mutated C217/454S-NTRC provided Arabidopsis with a similar degree of thermotolerance compared with that of NTRC°(E) plants. However, after prolonged incubation under heat shock, NTRC°(E) plants tolerated the stress to a higher degree than C217/454S-NTRC°(E) plants. The results suggest that the heat shock-mediated holdase chaperone function of NTRC is responsible for the increased thermotolerance of Arabidopsis and the activity is significantly supported by NADPH.

GSH-dependent peroxidase activity of the rice (Oryza sativa) glutaredoxin, a thioltransferase

Glutaredoxin (Grx) is a 12-kDa thioltransferase that reduces disulfide bonds of other proteins and maintains the redox potential of cells. In addition to its oxidoreductase activity, we report here that a rice Grx (OsGrx) can also function as a GSH-dependent peroxidase. Because of this antioxidant activity, OsGrx protects glutamine synthetase from oxidative damage. Individually replacing the conserved Cys residues in OsGrx with Ser shows that Cys(23), but not Cys(26), is essential for the thioltransferase and GSH-dependent peroxidase activities. Kinetic characterization of OsGrx reveals that the maximal catalytic efficiency (V(max)/K(m)) is obtained with cumene hydroperoxide rather than H(2)O(2) or t-butyl hydroperoxide.

Development of multiplex PCR-based detection method for five approved LM canola events in Korea

캐놀라(canola)는 식용유 및 바이오 에너지 생산을 위해 전 세계적으로 널리 재배되는 작물이다. 캐놀라의 수요가 증가하면서 유전자변형 캐놀라에 대한 중요성이 높아짐에 따라 LM 캐놀라 재배면적이 해마다 증가하고 있다. 국내에서는 상업적으로 활용되는 캐놀라를 100% 전량 수입에 의존하고 있으며, 이에 따라 비의도적으로 유출 가능성이 있는 수입 LM 캐놀라의 안전관리 및 생태계 위해성 평가가 요구된다. 본 연구에서는 국내 수입 승인 유통 LM 캐놀라 5개 이벤트(Topas 19/2, Rf3, Ms8, RT73, T45)의 명확한 검출을 위한 동시증폭 검출법(multiplex PCR)을 확립하고자 하였다. PCR 반응 조건은 5개 LM 이벤트가 동시에 명확히 검출되는 최적 primer 농도 및 반응 조건을 통해 Topas 19/2 (95 bp), Rf3 (139 bp), Ms8 (250 bp), RT73 (317 bp), T45 (378 bp)의 서로 다른 생성물 크기로 명확히 구분되도록 하였다. 최적 primer 농도는 반응액 최종농도 0.3~1.0 pmol로 primer 쌍 마다 각각 다른 cocktail을 만들었고, PCR 반응 조건은

Comparative molecular modeling study of Arabidopsis NADPH-dependent thioredoxin reductase and its hybrid protein.

95^{\circ}C

Algicidal effect of hybrid peptides as potential inhibitors of harmful algal blooms.

5분 반응 후,