Characterization of endoproteases from plant peroxisomes

Trametes coccinea IDEA, un hongo súper productor de lacasa aislado de un lago natural de asfalto: Tolerancia y biotransformación de hidrocarburos policíclicos aromáticos

Los hidrocarburos policíclicos aromáticos (HPAs) son compuestos tóxicos que no se degradan fácilmente bajo condiciones naturales tales como fenómenos físicos (fotooxidación, volatilización), químicos (intercambio iónico, complejación, transformación) y biológicos (degradación por microorganismos autóctonos) que además, dependen de la temperatura, humedad y niveles de oxígeno. El objetivo del presente trabajo fue aislar, identificar y caracterizar fenotípicamente hongos hidrocarbono clásticos de ambientes extremos que sean capaces de tolerar HPAs, tales como Trametes coccinea IDEA, que se aisló del Lago de asfalto natural de Guanoco en Venezuela. A fin de estudiar su tolerancia a los HPAs, el hongo se expuso a diferentes concentraciones de naftaleno, fenantreno y pireno (0, 2.5, 25, 50, 100, 200, 400, 800 y 1600 mg/L). Posteriormente, en ensayo en medio de cultivo líquido, se procedió a estudiar el efecto de los HPAs sobre la actividad de enzimas del sistema enzimático de degradación de lignina (SEDL), así como sobre la posible variación en los niveles de toxicidad empleando Lactuca sativa como bioindicador. Los resultados mostraron una mayor tolerancia al pireno, seguido por el naftaleno y fenantreno. Se observó una fuerte inducción de la actividad lacasa en presencia de naftaleno (167.96 U/mgP) y pireno (124.89 U/mgP) con respecto al control, mientras que con fenantreno se obtuvo una baja actividad (88.67 U / mgP). De manera interesante, se evidenció una generación de sub-productos más tóxicos cuando el naftaleno y el fenantreno fueron biotratados por el hongo, mientras que el nivel de toxicidad del pireno disminuyó significativamente. T. coccinea IDEA tiene un alto potencial para ser utilizado en estrategias de biorremediación de hidrocarburos, las cuales deben ser monitoreadas mediante análisis ecotoxicológicos para detectar posibles variaciones de toxicidad de los productos parcialmente biotransformados.

Cyclic AMP mediates heat stress response by the control of redox homeostasis and ubiquitin-proteasome system

Heat stress (HS), causing impairment in several physiological processes, is one of the most damaging environmental cues for plants. To counteract the harmful effects of high temperatures, plants activate complex signalling networks, indicated as HS response (HSR). Expression of heat shock proteins (HSPs) and adjustment of redox homeostasis are crucial events of HSR, required for thermotolerance. By pharmacological approaches, the involvement of cAMP in triggering plant HSR has been recently proposed. In this study, to investigate the role of cAMP in HSR signalling, tobacco BY-2 cells overexpressing the 'cAMP-sponge', a genetic tool that reduces intracellular cAMP levels, have been used. in vivo cAMP dampening increased HS susceptibility in a HSPs-independent way. The failure in cAMP elevation during HS caused a high accumulation of reactive oxygen species, due to increased levels of respiratory burst oxidase homolog D, decreased activities of catalase and ascorbate peroxidase, as well as down-accumulation of proteins involved in the control of redox homeostasis. In addition, cAMP deficiency impaired proteasome activity and prevented the accumulation of many proteins of ubiquitin-proteasome system (UPS). By a large-scale proteomic approach together with in silico analyses, these UPS proteins were identified in a specific cAMP-dependent network of HSR.

Carboxylated multi-walled carbon nanotubes exacerbated oxidative damage in roots of Vicia faba L. seedlings under combined stress of lead and cadmium

Multi-walled carbon nanotubes (MWCNTs) and heavy metals could be absorbed and bioaccumulated by agricultural crops, implicating ecological risks. Herein, the present study investigated the ecotoxicological effects and mechanisms of individual carboxylated MWCNTs (MWCNTs-COOH) (2.5, 5.0 and 10 mg/L) and their combination with 20 µM Pb and 5 µM Cd (shortened as Pb + Cd) on roots of Vicia faba L. seedlings after 20 days of exposure. The results showed that the tested MWCNTs-COOH induced imbalance of nutrient elements, enhanced isozymes and activities of superoxide dismutase (SOD), guaiacol peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), resulting in accumulation of carbonylated proteins, elevation of endoproteases (EPs) isozymes, and reduction of HSP70 synthesis in the roots. However, the tested MWCNTs-COOH facilitated the enrichment of Cd, Pb and Na elements, contributing to the decrease of SOD, CAT and APX activities, and the reduction of HSP70 synthesis, whereas the elevation of carbonylated proteins, EP activities and cell necrosis in the roots when Pb + Cd was combined in comparison to the treatments of MWCNTs-COOH, or Pb + Cd alone. Thus, the tested MWCNTs-COOH not only caused oxidative stress, but also aggravated the oxidative damage in the roots exposed to Pb + Cd in the culture solution.

Tolerance to Stress Combination in Tomato Plants: New Insights in the Protective Role of Melatonin

Abiotic stresses such as drought, heat or salinity are major causes of yield loss worldwide. Recent studies have revealed that the acclimation of plants to a combination of different environmental stresses is unique and therefore cannot be directly deduced from studying the response of plants to each of the different stresses applied individually. The efficient detoxification of reactive oxygen species (ROS) is thought to play a key role in enhancing the tolerance of plants to abiotic stresses. Here, we report on the role of melatonin in the protection of the photosynthetic apparatus through the increase in ROS detoxification in tomato plants grown under the combination of salinity and heat, two of the most common abiotic stresses known to act jointly. Plants treated with exogenous melatonin showed a different modulation in the expression on some antioxidant-related genes and their related enzymes. More specifically, ascorbate peroxidase, glutathione reductase, glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase (APX, GR, GPX and Ph-GPX, resepctively) showed an antagonistic regulation as compared to plants that did not receive melatonin. This translated into a better antioxidant capacity and to a lesser ROS accumulation under stress combination. The performance of the photosynthesis parameters and the photosystems was also increased in plants treated with exogenous melatonin under the combination of salinity and heat. In accordance with these findings, tomato plants treated with melatonin were found to grow better under stress combination that the non-treated ones. Our study highlights the important role that exogenous melatonin plays in the acclimation of plants to a combination of two different abiotic stresses, and how this compound can specifically regulate oxidative stress-related genes and enzymes to increase plant tolerance.

Proteome of Plant Peroxisomes

Plant peroxisomes are required for a number of fundamental physiological processes, such as primary and secondary metabolism, development and stress response. Indexing the dynamic peroxisome proteome is prerequisite to fully understanding the importance of these organelles. Mass Spectrometry (MS)-based proteome analysis has allowed the identification of novel peroxisomal proteins and pathways in a relatively high-throughput fashion and significantly expanded the list of proteins and biochemical reactions in plant peroxisomes. In this chapter, we summarize the experimental proteomic studies performed in plants, compile a list of ~200 confirmed Arabidopsis peroxisomal proteins, and discuss the diverse plant peroxisome functions with an emphasis on the role of Arabidopsis MS-based proteomics in discovering new peroxisome functions. Many plant peroxisome proteins and biochemical pathways are specific to plants, substantiating the complexity, plasticity and uniqueness of plant peroxisomes. Mapping the full plant peroxisome proteome will provide a knowledge base for the improvement of crop production, quality and stress tolerance.

Unraveling of the Structure and Function of Peroxisomal Protein Import Machineries

Peroxisomes are dynamic organelles of eukaryotic cells performing a wide range of functions including fatty acid oxidation, peroxide detoxification and ether-lipid synthesis in mammals. Peroxisomes lack their own DNA and therefore have to import proteins post-translationally. Peroxisomes can import folded, co-factor bound and even oligomeric proteins. The involvement of cycling receptors is a special feature of peroxisomal protein import. Complex machineries of peroxin (PEX) proteins mediate peroxisomal matrix and membrane protein import. Identification of PEX genes was dominated by forward genetic techniques in the early 90s. However, recent developments in proteomic techniques has revolutionized the detailed characterization of peroxisomal protein import. Here, we summarize the current knowledge on peroxisomal protein import with emphasis on the contribution of proteomic approaches to our understanding of the composition and function of the peroxisomal protein import machineries.

ROS Generation in Peroxisomes and its Role in Cell Signaling

In plant cells, as in most eukaryotic organisms, peroxisomes are probably the major sites of intracellular H₂O₂ production, as a result of their essentially oxidative type of metabolism. In recent years, it has become increasingly clear that peroxisomes carry out essential functions in eukaryotic cells. The generation of the important messenger molecule hydrogen peroxide (H₂O₂) by animal and plant peroxisomes and the presence of catalase in these organelles has been known for many years, but the generation of superoxide radicals (O₂^·- ) and the occurrence of the metalloenzyme superoxide dismutase was reported for the first time in peroxisomes from plant origin. Further research showed the presence in plant peroxisomes of a complex battery of antioxidant systems apart from catalase. The evidence available of reactive oxygen species (ROS) production in peroxisomes is presented, and the different antioxidant systems characterized in these organelles and their possible functions are described. Peroxisomes appear to have a ROS-mediated role in abiotic stress situations induced by the heavy metal cadmium (Cd) and the xenobiotic 2,4-D, and also in the oxidative reactions of leaf senescence. The toxicity of Cd and 2,4-D has an effect on the ROS metabolism and speed of movement (dynamics) of peroxisomes. The regulation of ROS production in peroxisomes can take place by post-translational modifications of those proteins involved in their production and/or scavenging. In recent years, different studies have been carried out on the proteome of ROS metabolism in peroxisomes. Diverse evidence obtained indicates that peroxisomes are an important cellular source of different signaling molecules, including ROS, involved in distinct processes of high physiological importance, and might play an important role in the maintenance of cellular redox homeostasis.

Investigation of plant latices of Asteraceae and Campanulaceae regarding proteolytic activity

Occurrence of plant latices is widespread, there are more than 40 families of plants characterized to establish lactiferous structures. The appearance of hydrolytic active proteins, incorporated in latices is already characterized, and hydrolytic active proteins are considerable, and for several plant families, the occurrence of hydrolytic active proteins is already specified e.g. Apocynaceae Juss., Caricaceae Dumort, Euphorbiaceae Juss., Moraceae Gaudich and Papaveraceae Juss. In our investigation, focused on latex bearing plants of order Asterales, Asteraceae and Campanulaceae in particular. The present outcomes represent a comprehensive study, relating to the occurrence of proteolytic active enzymes of order Asterales for the first time. 131 different species of Asteraceae and Campanulaceae were tested, and the appearance of plant latex proteases were determined in different quantities. Proteolytic activity was investigated by inhibitory studies and determination of residual activity in the following, enable us to characterize the proteases. Most of the considered species exhibit a serine protease activity and a multiplicity of species exhibited two or more subclasses of proteases.

The combined effect of salinity and heat reveals a specific physiological, biochemical and molecular response in tomato plants

Many studies have described the response mechanisms of plants to salinity and heat applied individually; however, under field conditions some abiotic stresses often occur simultaneously. Recent studies revealed that the response of plants to a combination of two different stresses is specific and cannot be deduced from the stresses applied individually. Here, we report on the response of tomato plants to a combination of heat and salt stress. Interestingly, and in contrast to the expected negative effect of the stress combination on plant growth, our results show that the combination of heat and salinity provides a significant level of protection to tomato plants from the effects of salinity. We observed a specific response of plants to the stress combination that included accumulation of glycine betaine and trehalose. The accumulation of these compounds under the stress combination was linked to the maintenance of a high K(+) concentration and thus a lower Na(+) /K(+) ratio, with a better performance of the cell water status and photosynthesis as compared with salinity alone. Our findings unravel new and unexpected aspects of the response of plants to stress combination and provide a proposed list of enzymatic targets for improving crop tolerance to the abiotic field environment.

Highly oxidized peroxisomes are selectively degraded via autophagy in Arabidopsis

The positioning of peroxisomes in a cell is a regulated process that is closely associated with their functions. Using this feature of the peroxisomal positioning as a criterion, we identified three Arabidopsis thaliana mutants (peroxisome unusual positioning1 [peup1], peup2, and peup4) that contain aggregated peroxisomes. We found that the PEUP1, PEUP2, and PEUP4 were identical to Autophagy-related2 (ATG2), ATG18a, and ATG7, respectively, which are involved in the autophagic system. The number of peroxisomes was increased and the peroxisomal proteins were highly accumulated in the peup1 mutant, suggesting that peroxisome degradation by autophagy (pexophagy) is deficient in the peup1 mutant. These aggregated peroxisomes contained high levels of inactive catalase and were more oxidative than those of the wild type, indicating that peroxisome aggregates comprise damaged peroxisomes. In addition, peroxisome aggregation was induced in wild-type plants by exogenous application of hydrogen peroxide. The cat2 mutant also contained peroxisome aggregates. These findings demonstrate that hydrogen peroxide as a result of catalase inactivation is the inducer of peroxisome aggregation. Furthermore, an autophagosome marker, ATG8, frequently colocalized with peroxisome aggregates, indicating that peroxisomes damaged by hydrogen peroxide are selectively degraded by autophagy in the wild type. Our data provide evidence that autophagy is crucial for quality control mechanisms for peroxisomes in Arabidopsis.

Purification, characterization and identification of a senescence related serine protease in dark-induced senescent wheat leaves

Senescence-related proteases play important roles in leaf senescence by regulating protein degradation and nutrient recycling. A 98.9kDa senescence-related protease EP3 in wheat leaves was purified by ammonium sulfate precipitation, Q-Sepharose fast flow anion exchange chromatography and gel slicing after gel electrophoresis. Due to its relatively high thermal stability, its protease activity did not decrease after incubation at 40°C for 1-h. EP3 protease was suggested to be a metal-dependent serine protease, because its activity was inhibited by serine protease inhibitors PMSF and AEBSF and metal related protease inhibitor EGTA. It was identified as a subtilisin-like serine protease of the S8A family based on data from both mass spectrometry and the cloned cDNA sequence. Therefore, these data suggest that a serine protease of the S8A subfamily with specific biochemical properties is involved in senescence-associated protein degradation.

Role of peroxisomes as a source of reactive oxygen species (ROS) signaling molecules

Peroxisomes are very dynamic and metabolically active organelles and are a very important source of reactive oxygen species (ROS), H2O2, O2 (.-) and · OH, which are mainly produced in different metabolic pathways, including fatty acid β-oxidation, photorespiration, nucleic acid and polyamine catabolism, ureide metabolism, etc. ROS were originally associated to oxygen toxicity; however, these reactive species also play a central role in the signaling network regulating essential processes in the cell. Peroxisomes have the capacity to rapidly produce and scavenge H2O2 and O2 (.-) which allows to regulate dynamic changes in ROS levels. This fact and the plasticity of these organelles, which allows adjusting their metabolism depending on different developmental and environmental cues, makes these organelles play a central role in cellular signal transduction. The use of catalase and glycolate oxidase loss-of-function mutants has allowed to study the consequences of changes in the levels of endogenous H2O2 in peroxisomes and has improved our knowledge of the transcriptomic profile of genes regulated by peroxisomal ROS. It is now known that peroxisomal ROS participate in more complex signaling networks involving calcium, hormones, and redox homeostasis which finally determine the response of plants to their environment.

Biphasic effects of lanthanum on Vicia faba L. seedlings under cadmium stress, implicating finite antioxidation and potential ecological risk

In the present study, lanthanum (La) as a representative REE was used to explore the mechanisms for alleviation of Cd-induced oxidative damage by extraneous La at appropriate concentrations, and to assess ecological risk of combination of Cd and La at higher concentrations in roots of Vicia faba L. seedlings. The seedlings were hydroponically cultured for 15 d under nutrient solution, 6 μmol L(-1) CdCl(2), and combination of 6 μmol L(-1) CdCl(2) and increasing concentrations of La, respectively. The results showed that the supplementation with low concentrations of exogenous La (<120 μmol L(-1)) led to reduced contents of Cd, Ca, Cu, Zn, Mn or Fe element and increased activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) isozymes as well as heat shock protein 70 (HSP 70) production in the roots. However, the supplementation with higher La (>120 μmol L(-1)) showed the adverse effects. The contents of Cd elevated above the single Cd treatment in the roots, accompanying with the decline of antioxidant isozyme's activities and HSP 70, and increment of carbonylated proteins and endoprotease isozyme's activities. The results also showed that the root growth was not only related to carbonylated proteins, but also to indole acetic acid oxidase activities. Therefore, the supplemented extraneous La contributed to biphasic effects: stimulated antioxidation at lower concentrations and pro-oxidation at higher concentrations against Cd-induced oxidative stress in the roots.

Toxicological effects involved in risk assessment of rare earth lanthanum on roots of Vicia faba L. seedlings

Combined chemical analyses and biological measurements were utilized to investigate potential toxicological effects and possible mechanisms involved in risk assessment of rare earth elements (REEs) on Vicia faba L. seedlings, which were hydroponically cultivated and exposed to various concentrations of lanthanum (La) for 15 days. The results showed that La contents in both the solution and roots increased with the increase of extraneous La, contributing to hormetic dose responses of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX) and endoprotease (EP) isozymes activities, and HSP 70 production enhanced at low doses but suppressed at higher doses of La. These physiological responses constituted antioxidant and detoxification systems against La-induced oxidative stress. The elevated La levels also contributed to oxidatively modified proteins, which were most responsible for subsequent cell death and growth retardation of the roots. By combination of hormetic and traditional threshold dose levels, the threshold dose range was deduced to be 108-195 microg La/g dry weight in the roots, corresponding to 0.90-3.12 mg/L of soluble La in the culture solution. It suggests that persistent applications of REEs may lead to potential ecological risk in the environment.

Hormesis effects and implicative application in assessment of lead-contaminated soils in roots of Vicia faba seedlings

Chemical analyses and biological methods were combined to investigate oxidative stress, hormesis effect and concerned mechanism in roots of Viciafaba seedlings grown in 0-2000 mg kg(-1) of Pb-treated soils after germination of 20d. The results showed that U-shaped dose response curves were displayed in superoxide radical (O2-) radicals, guaiacol peroxidase (POD) and ascorbate peroxidase (APX) activities, malondialdehyde (MDA) and carbonyl groups as well as activities of endoproteinase (EP) isoenzymes in the roots at low doses of extraneous Pb, indicating reduced oxidative stress and toxic effect. The inverted U-shaped curves were also exhibited in growth height, superoxide dismutase (SOD) and EP activities as well as inducible heat shock protein70 (HSP70) with the increasing extraneous Pb, indicative of enhanced oxidative stress. The enhancement in HSP70, carbonyl groups and EP activities confirmed intracellular proteotoxicity and proteolytic activity in the roots at higher doses of soil Pb. More interestingly, levels of inducible HSP70 were well correlated with those of growth heights (r=0.809, p<0.05), implying that HSP70 induction may be one of the mechanisms underlying the U-shaped growth curve of V. faba seedlings in the experiment. The results suggest that traditional threshold models ought to be combined with hormesis effect in assessment of Pb-polluted soils and the threshold dose range of Pb-treated soils is proposed rudimentally as 25-125 mg kg(-1).

Peroxisome biogenesis and function

Peroxisomes are small and single membrane-delimited organelles that execute numerous metabolic reactions and have pivotal roles in plant growth and development. In recent years, forward and reverse genetic studies along with biochemical and cell biological analyses in Arabidopsis have enabled researchers to identify many peroxisome proteins and elucidate their functions. This review focuses on the advances in our understanding of peroxisome biogenesis and metabolism, and further explores the contribution of large-scale analysis, such as in sillco predictions and proteomics, in augmenting our knowledge of peroxisome function In Arabidopsis.

Peroxisomal xanthine oxidoreductase: characterization of the enzyme from pea (Pisum sativum L.) leaves

The presence and properties of the enzyme xanthine oxidoreductase (XOR) in peroxisomes from pea (Pisum sativum L.) leaves were studied using biochemical and immunological methods. The activity analysis showed that, in leaf peroxisomes, the superoxide-generating XOR form, xanthine oxidase (XOD), was predominant over the xanthine dehydrogenase form (XDH), with a XDH/XOD ratio of 0.5. However, in crude extracts of pea leaves, the XDH form was more abundant, with a XDH/XOD ratio of 1.6. The native molecular mass of the peroxisomal XOR determined by polyacrylamide gel electrophoresis was 290 kDa. Using western blot assays, we identified an immunoreactive band of 59 kDa that was not affected by the reducing reagent DTT or endogenous proteases. The analysis of pea leaves by electron microscopy immunogold labeling with affinity-purified antibodies against rat XOD confirmed that this enzyme was localized in the matrix of peroxisomes, as well as in chloroplasts and cytosol. In pea plants subjected to abiotic stress by cadmium, the activity of the peroxisomal XOR was reduced, whereas its protein level expression increased. The results confirmed that leaf peroxisomes contain XOR, and suggest that this peroxisomal metalloflavoprotein enzyme is involved in the mechanism of response of pea plants to abiotic stress by heavy metals.

Protein extraction for proteome analysis from cacao leaves and meristems, organs infected by Moniliophthora perniciosa, the causal agent of the witches' broom disease

Preparation of high-quality proteins from cacao vegetative organs is difficult due to very high endogenous levels of polysaccharides and polyphenols. In order to establish a routine procedure for the application of proteomic and biochemical analysis to cacao tissues, three new protocols were developed; one for apoplastic washing fluid (AWF) extraction, and two for protein extraction--under denaturing and nondenaturing conditions. The first described method allows a quick and easy collection of AWF--using infiltration-centrifugation procedure--that is representative of its composition in intact leaves according to the smaller symplastic contamination detected by the use of the hexose phosphate isomerase marker. Protein extraction under denaturing conditions for 2-DE was remarkably improved by the combination of chemically and physically modified processes including phenol, SDS dense buffer and sonication steps. With this protocol, high-quality proteins from cacao leaves and meristems were isolated, and for the first time well-resolved 1-DE and 2-DE protein patterns of cacao vegetative organs are shown. It also appears that sonication associated with polysaccharide precipitation using tert-butanol was a crucial step for the nondenaturing protein extraction and subsequent enzymatic activity detection. It is expected that the protocols described here could help to develop high-level proteomic and biochemical studies in cacao also being applicable to other recalcitrant plant tissues.

Physiology and biochemistry of source-regulated protein accumulation in the wheat grain

Wheat is unique among cereals for the baking qualities of its flour, which are dependent upon the type and concentration of its proteins. As a consequence, the grain protein concentration (GPC) is one of the main determinants of wheat international market price. More than 50-70% of the final grain N is accumulated before flowering and later remobilized to the grain, N fertilization being the common practice used to produce high GPC. However, after incremental additions of N fertilizer, GPC reaches a maximum and then remains constant, without any increase in N uptake or remobilization by the crop, thus decreasing the efficiency of N fertilizer. Although, the genetic and molecular mechanisms that regulate N uptake by the roots are being clarified quickly, the regulation and physiology of N transport from the leaves to the grain remains less clear. In this review, the possible regulatory points involved in N transport to the grain and the difficulties for increasing GPC are discussed. It has been demonstrated that protein synthesis in the grain is source-limited, and that the grain can accumulate protein limited only by the amino acids provided by the phloem. It has also been shown that there is no limitation in the amino acid/sugar ratios that can be exported to the phloem. On the other hand, NO(3)(-) uptake transporters are depressed when the plant concentration of some amino acids, such as glutamine, is high. It has also been shown that a high N supply increases cytokinins concentration, preventing leaf senescence and proteolysis. Based on this information, it is postulated that there are two main regulatory points during grain filling when plant N status is ample. On the one hand, the N uptake transporters in the roots are depressed due to the high amino acids concentration in the tissues, and N uptake is low. On the other, a high amino acids concentration keeps the cytokinins level high, repressing leaf protein degradation and decreasing amino acid export to the phloem. As a consequence, GPC cannot be increased despite the ample N supply.

Classes and crossreactivity of proteinases in the excretory–secretory products of Caenorhabditis elegans

Proteinases released during the in vitro maintenance of asynchronous cultures of the free-living nematode Caenorhabditis elegans were characterized on the basis of subunit composition, fluorogenic substrate specificity, inhibitor sensitivity and pH optima. Cysteine proteinases are present in the excretory–secretory products (ESP) as indicated by the hydrolysis of cathepsin fluorogenic substrates and confirmed by immunoblotting. Serine proteinases were predominant as indicated by substrate gel analysis and inhibitor studies. The presence of metallo-proteinases was also indicated by inhibitor studies. The optimal pH value for cysteine proteinases was 5.5, while serine proteinases were optimal at pH 8.0. As a control, cultures of Escherichia coli, the diet of C. elegans, were extracted separately and gave no evidence of overlap with C. elegans ESP. Cross reactivity between the ESP of C. elegans and antibodies raised against the ESP of the equine parasite Strongylus vulgaris indicated antigenic relatedness of a proteic epitope. This is the first study to characterize the ESP of C. elegans and to display its relatedness with that of S. vulgaris.

The two main endoproteases present in dark-induced senescent wheat leaves are distinct subtilisin-like proteases

We have previously reported the occurrence of two serine endoproteases (referred to as P1 and P2) in dark-induced senescent wheat (Triticum aestivum L.) leaves. P1 enzyme was already purified and identified as a subtilisin-like serine endoprotease (Roberts et al. in Physiol Plant 118:483-490, 2003). In this paper, we demonstrate by Western blot analysis of extracts obtained from dark-induced senescent leaves that an antiserum raised against P1 was able to recognise a second protein band of 78 kDa which corresponded to P2 activity. This result suggested that both enzymes must be structurally related. Therefore, we purified and characterised P2 activity. According to its biochemical and physical properties (inhibition by chymostatin and PMSF, broad pH range of activity, thermostability and ability to hydrolyse Suc-AAPF-pNA) P2 was classified as a serine protease with chymotrypsin-like activity. In addition, P2 was identified by mass spectrometry as a subtilisin-like protease distinct from P1. Western blot analysis demonstrated that P1 appeared in extracts from non-detached dark-induced senescent leaves but was undetectable in leaves senescing after nitrogen (N) deprivation. In contrast, P2 was already present in non-senescent leaves and showed increased levels in leaves senescing after N starvation or incubation in darkness. P1 signal was detected at late stages of ethephon or methyl jasmonate-induced senescence but was undetectable in senescent leaves from plants treated with abscisic acid. None of the three hormones have any effect on P2 protein levels. These results indicate that despite their biochemical and structural similarities, both enzymes are probably involved in different physiological roles.

Characterization of cysteine proteases in Malian medicinal plants

Extracts form 10 different Malian medicinal plants with a traditional use against schistosomiasis were investigated for their possible content of proteolytic activity. The proteolytic activity was studied by measuring the hydrolysis of two synthetic peptide substrates Z-Ala-Ala-Asn-NHMec and Z-Phe-Arg-NHMec. Legumain- and papain-like activities were found in all tested crude extracts except those from Entada africana, with the papain-like activity being the strongest. Cissus quadrangularis, Securidaca longepedunculata and Stylosanthes erecta extracts showed high proteolytic activities towards both substrates. After gel filtration the proteolytic activity towards the substrate Z-Ala-Ala-Asn-NHMec in root extract of Securidaca longepedunculata appeared to have Mr of 30 and 97kDa, while the activity in extracts from Cissus quadrangularis was at 39kDa. Enzymatic activity cleaving the substrate Z-Phe-Arg-NHMec showed apparent Mr of 97 and 26kDa in extracts from roots and leaves of Securidaca longepedunculata, while in Cissus quadrangularis extracts the activity eluted at 39 and 20kDa, with the highest activity in the latter. All Z-Phe-Arg-NHMec activities were inhibited by E-64 but unaffected by PMSF. The legumain activity was unaffected by E-64 and PMSF. The SDS-PAGE analysis exhibited five distinct gelatinolytic bands for Cissus quadrangularis extracts (115, 59, 31, 22 and 20kDa), while two bands (59 and 30kDa) were detected in Securidaca longepedunculata extracts. The inhibition profile of the gelatinolytic bands and that of the hydrolysis of the synthetic substrates indicate the cysteine protease class of the proteolytic activities. Several cysteine protease activities with different molecular weights along with a strong variability of these activities between species as well as between plant parts from the same species were observed.

Glutathione reductase from pea leaves: response to abiotic stress and characterization of the peroxisomal isozyme

The glutathione reductase (GR; EC 1.6.4.2) isozyme present in peroxisomes has been purified for the first time, and its unequivocal localization in these organelles, by immunogold electron microscopy, is reported. The enzyme was purified c. 21-fold with a specific activity of 9523 units mg(-1) protein, and a yield of 44 microg protein kg(-1) leaves was obtained. The subunit size of the peroxisomal GR was 56 kDa and the isoelectric point was 5.4. The enzyme was recognized by a polyclonal antibody raised against total GR from pea (Pisum sativum) leaves. The localization of GR in peroxisomes adds to chloroplasts and mitochondria where GR isozymes are also present, and suggests a multiple targeting of this enzyme to distinct cell compartments depending on the metabolism of each organelle under the plant growth conditions. The expression level of GR in several organs of pea plants and under different stress conditions was investigated. The possible role of peroxisomal GR under abiotic stress conditions, such as cadmium toxicity, high light, darkness, high temperature, wounding and low temperature, is discussed.

Characterization of senescence-associated proteases in postharvest broccoli florets

We characterized the senescence-associated proteases of postharvest broccoli (Brassica oleracea L. var Green King) florets, using class-specific protease inhibitors and gelatin-polyacrylamide gel electrophoresis. Different classes of senescence-associated proteases in broccoli florets were partially characterized for the first time. Protease activity of broccoli florets was depressed by all the inhibitors and showed different inhibition curves during postharvest. The hydrolytic activity of metalloprotease (EC 3.4.24. - ) and serine protease (EC 3.4.21. - ) reached a maximum, 1 day after harvest (DAH), then decreased, while the hydrolytic activity of cysteine protease (EC 3.4.22. - ) and aspartic protease (EC 3.4.23. - ) increased throughout the postharvest senescence based on the calculated inhibition percentage of protease activity. The senescence-associated proteases were separated into seven endoprotease (EP) groups by gelatin-polyacryamide gel electrophoresis and classified into EP1 (metalloprotease), EP2 (metalloprotease and cysteine protease), EP3 (serine protease and aspartic protease), EP4, EP5, EP7 (cysteine protease), and EP6 (serine protease) based on the sensitivity of class-specific protease inhibitors. The proteases EP2, EP3, and EP4 were present throughout the postharvest stages. EP3 was the major EP at all times during senescence; EP4 intensity of activity increased after 2 DAH; EP6 and EP7 clearly increased after 4 DAH. Our results suggest that serine protease activity contributes to early stage (0-1 DAH) and late stage (4-5 DAH) of senescence; metalloprotease activity was involved in the early and intermediate stages (0-3 DAH) of senescence; and cysteine protease and aspartic protease activities participated in the whole process of broccoli senescence.

Different classes of proteases are involved in the response to drought of Phaseolus vulgaris L. cultivars differing in sensitivity

Protein breakdown and recycling, which depend on the levels of proteolytic enzymes, are an essential part of the plant response to environmental stress. In order to study changes in the activity of proteases in Phaseolus vulgaris L. subjected to water deficit, three cultivars of European origin that exhibit different degrees of sensitivity to drought were chosen on the basis of changes in water potential, psiw, water and protein contents of leaves during progressive water deficit, and loss of membrane integrity after osmotic stress. Twenty-day-old plants were subjected to water deficit by withholding irrigation. Specific enzyme activities in leaf extracts were determined for plants under different degrees of drought stress using different substrates and protease inhibitors. Proteolytic activities were partially characterized by gel exclusion chromatography. Activities of two of the three identified serine proteinases changed under water deficit. The activity of the one with apparent molecular mass of approximately 65 kDa was observed to increase progressively with increasing withdrawal of water in the more sensitive cultivars, but to decrease in the more resistant cultivar. The same activity was elevated in senescent leaves. Under conditions of severe water deficit, the most sensitive cultivar exhibited a marked increase in the activity of two different aminopeptidases, while the more resistant cultivar showed a significant decrease in the activity of these aminopeptidases. These results point to complex and probably specific roles for different proteases in the plant response to drought.

Peroxisomes from pepper fruits (Capsicum annuum L.): purification, characterisation and antioxidant activity

Pepper is a vegetable of importance in human nutrition. Currently, one of the most interesting properties of natural products is their antioxidant content. In this work, the purification and characterisation of peroxisomes from fruits of a higher plant was carried out, and their antioxidative enzymatic and non-enzymatic content was investigated. Green and red pepper fruits (Capsicum annuum L., type Lamuyo) were used in this study. The analysis by electron microscopy showed that peroxisomes from both types of fruits contained crystalline cores which varied in shape and size, and the presence of chloroplasts and chromoplasts in green and red pepper fruits, respectively, was confirmed. Peroxisomes were purified by differential and sucrose density-gradient centrifugations. In the peroxisomal fractions, the activity of the photorespiration, beta-oxidation and glyoxylate cycle enzymes, and the ROS-related enzymes catalase, superoxide dismutase, xanthine oxidase, glutathione reductase and NADP(+)-dehydrogenases, was determined. Most enzymes studied had higher specific activity and protein content in green than in red fruits. By native PAGE and western blot analysis, the localisation of a Mn-SOD in fruit peroxisomes was demonstrated. The ascorbate and glutathione levels were also determined in crude extracts and in peroxisomes purified from both green and red peppers. The total ascorbate content (200-220 mg per 100 g FW) was similar in crude extracts from the two types of fruits, but higher in peroxisomes from red peppers. The glutathione concentration was 2-fold greater in green pepper crude extracts than in red fruits, whereas peroxisomes from both tissues showed similar values. The presence in pepper peroxisomes of different antioxidative enzymes and their corresponding metabolites implies that these organelles might be an important pool of antioxidants in fruit cells, where these enzymes could also act as modulators of signal molecules (O2*-, H202) during fruit maturation.

Reactive oxygen species, antioxidant systems and nitric oxide in peroxisomes

Peroxisomes are subcellular organelles with an essentially oxidative type of metabolism. Like chloroplasts and mitochondria, plant peroxisomes also produce superoxide radicals (O2*(-)) and there are, at least, two sites of superoxide generation: one in the organelle matrix, the generating system being xanthine oxidase, and another site in the peroxisomal membranes dependent on NAD(P)H. In peroxisomal membranes, three integral polypeptides (PMPs) with molecular masses of 18, 29 and 32 kDa have been shown to generate radicals O2*(-). Besides catalase, several antioxidative systems have been demonstrated in plant peroxisomes, including different superoxide dismutases, the ascorbate-glutathione cycle, and three NADP-dependent dehydrogenases. A CuZn-SOD and two Mn-SODs have been purified and characterized from different types of peroxisomes. The four enzymes of the ascorbate-glutathione cycle (ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase) as well as the antioxidants glutathione and ascorbate have been found in plant peroxisomes. The recycling of NADPH from NADP(+) can be carried out in peroxisomes by three dehydrogenases: glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and isocitrate dehydrogenase. In the last decade, different experimental evidence has suggested the existence of cellular functions for peroxisomes related to reactive oxygen species (ROS), but the recent demonstration of the presence of nitric oxide synthase (NOS) in plant peroxisomes implies that these organelles could also have a function in plant cells as a source of signal molecules like nitric oxide (NO*), superoxide radicals, hydrogen peroxide, and possibly S-nitrosoglutathione (GSNO).

Monomeric alcohol oxidase is preferentially digested by a novel protease from Candida boidinii

A protease activity has been partially purified from peroxisomal matrix fractions of the methylotrophic yeast Candida boidinii. The enzyme migrates as a single peak on a sucrose velocity gradient with an apparent native molecular mass of approximately 80-90 kDa. Activity can be recovered from nonreducing sodium dodecyl sulfate gels as a approximately 20 kDa species, suggesting it is an oligomer. The protein exhibits chymotrypsin-like activity and cleaves the model compound suc-L-L-V-Y-AMC. Additionally, monomers of alcohol oxidase (AO), an abundant protein of C. boidinii peroxisomes, generated in vitro or in pulse-radiolabeled cells, are preferentially sensitive to degradation by the protease. Sensitivity is lost over time in vivo as AO folds and matures into octamers, suggesting that the protease may be involved in these processes.

Peroxisomes as a source of reactive oxygen species and nitric oxide signal molecules in plant cells

The important role of plant peroxisomes in a variety of metabolic reactions such as photorespiration, fatty acid beta-oxidation, the glyoxylate cycle and generation-degradation of hydrogen peroxide is well known. In recent years, the presence of a novel group of enzymes, mainly involved in the metabolism of oxygen free-radicals, has been shown in peroxisomes. In addition to hydrogen peroxide, peroxisomes can generate superoxide-radicals and nitric oxide, which are known cellular messengers with a variety of physiological roles in intra- and inter-cellular communication. Nitric oxide and hydrogen peroxide can permeate the peroxisomal membrane and superoxide radicals can be produced on the cytosolic side of the membrane. The signal molecule-generating capacity of peroxisomes can have important implications for cellular metabolism in plants, particularly under biotic and abiotic stress.

Localization of nitric-oxide synthase in plant peroxisomes

The presence of nitric-oxide synthase (NOS) in peroxisomes from leaves of pea plants (Pisum sativum L.) was studied. Plant organelles were purified by differential and sucrose density gradient centrifugation. In purified intact peroxisomes a Ca(2+)-dependent NOS activity of 5.61 nmol of L-[(3)H]citrulline mg(-1) protein min(-1) was measured while no activity was detected in mitochondria. The peroxisomal NOS activity was clearly inhibited (60-90%) by different well characterized inhibitors of mammalian NO synthases. The immunoblot analysis of peroxisomes with a polyclonal antibody against the C terminus region of murine iNOS revealed an immunoreactive protein of 130 kDa. Electron microscopy immunogold-labeling confirmed the subcellular localization of NOS in the matrix of peroxisomes as well as in chloroplasts. The presence of NOS in peroxisomes suggests that these oxidative organelles are a cellular source of nitric oxide (NO) and implies new roles for peroxisomes in the cellular signal transduction mechanisms.

Evidence of a role for plant proteases in the degradation of herbage proteins in the rumen of grazing cattle

Protein breakdown in the rumen is generally regarded as a two-stage process in which proteases produced by rumen microorganisms cleave plant protein into peptides and amino acids. However, many of the fiber-degrading cellulolytic species in the rumen are not in fact proteolytic, and the proteolytic activity of the entire rumen microbial population is only moderate when compared to the gastric and pancreatic secretions in the abomasum. Moreover, plant cell walls remain largely intact after initial chewing (particularly in cattle), presenting a physical barrier that must be breached prior to their effective colonization. The present study considers the hypothesis that the plant enzymes are at least partly responsible for herbage protein degradation in grazing ruminants. Ryegrass, red clover, white clover, and bird's-foot trefoil were incubated in the presence and absence of rumen microorganisms. The production of volatile fatty acids indicated the level of microbial activity, whereas the relative disappearance of the large subunit of ribulose 1,5 bisphosphate carboxylase/oxygenase (Rubisco LSU) indicated proteolytic activity. In all incubations, the relative abundance of the Rubisco LSU decreased as the incubation progressed. When rumen microorganisms were absent, low molecular weight peptides (below 20 kDa) accumulated as the incubation progressed. This accumulation was not observed in the presence of rumen microorganisms. Therefore we suggest that the intrinsic plant proteases contribute to the initial stages of proteolysis of grazed herbage.

Peroxisomal NADP-Dependent Isocitrate Dehydrogenase. Characterization and Activity Regulation during Natural Senescence

The peroxisomal localization and characterization of NADP-dependent isocitrate dehydrogenase (perICDH) in young and senescent pea (Pisum sativum) leaves was studied by subcellular fractionation, kinetic analysis, immunoblotting, and immunoelectron microscopy. The subunit molecular mass for perICDH determined by immunoblotting was 46 kD. By isoelectric focusing (IEF) of the peroxisomal matrix fraction, the NADP-ICDH activity was resolved into four isoforms, perICDH-1 to perICDH-4, with isoelectric points (pIs) of 6.0, 5.6, 5.4, and 5.2, respectively. The kinetic properties of the NADP-ICDH in peroxisomes from young and senescent pea leaves were analyzed. The maximum initial velocity was the same in peroxisomes from young and senescent leaves, while the Michaelis constant value in senescent leaf peroxisomes was 11-fold lower than in young leaf peroxisomes. The protein levels of NADP-ICDH in peroxisomes were not altered during senescence. The kinetic behavior of this enzyme suggests a possible fine control of enzymatic activity by modulation of its Michaelis constant during the natural senescence of pea leaves. After embedding, electron microscopy immunogold labeling of NADP-ICDH confirmed that this enzyme was localized in the peroxisomal matrix. Peroxisomal NADP-ICDH represents an alternative dehydrogenase in these cell organelles and may be the main system for the reduction of NADP to NADPH for its re-utilization in the peroxisomal metabolism.

In vitro processing of the human alkyl-dihydroxyacetonephosphate synthase precursor

Alkyl-dihydroxyacetonephosphate synthase, a peroxisomal enzyme involved in the biosynthesis of ether phospholipids, is synthesized with a cleavable N-terminal presequence containing the peroxisomal targeting signal type 2. The human alkyl-dihydroxyacetonephosphate synthase precursor produced in vitro or expressed in Escherichia coli could be processed to a lower molecular weight protein by incubation at 37 degrees C with a guinea pig liver fraction, enriched in mitochondria, lysosomes, and peroxisomes. This lower molecular weight protein was identified as the mature human alkyl-dihydroxyacetonephosphate synthase by radiosequencing, indicating that the processing protease is present in this organellar fraction. Characterization of the processing protease indicated that it is a cysteine protease with a pH optimum of 6.5. Furthermore, it was demonstrated that exogenously added pre-alkyl-dihydroxyacetonephosphate synthase was imported and processed in purified peroxisomes in vitro. Processing of alkyl-dihydroxyacetonephosphate synthase did not increase the activity of the enzyme. This indicates that the presence of the presequence does not affect the activity of the enzyme.

Detection of protease activities using specific aminoacyl or peptidyl p-nitroanilides after sodium dodecyl sulfate - polyacrylamide gel electrophoresis and its applications

A general method for detecting protease activities on acrylamide or agarose gels after sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE) using specific aminoacyl p-nitroanilide (NA) or peptidyl NA as substrate is described. This method is extended from the spectrophotometric assay of p-nitroaniline, which is a chromogenic product liberated by protease action on aminoacyl NA or peptidyl NA. The acrylamide gel containing protein bands was dipped directly into a solution which contained specific synthetic aminoacyl NA or peptidyl NA as a substrate or had been overlaid with an agarose gel containing the same substrate. The p-nitroaniline released on the acrylamide or agarose gel by the specific protease was diazotized with sodium nitrite and then coupled to N-(1-naphthyl)-ethylenediamine to produce distinct activity band(s). The substrates used for protease activity staining on gels were identical to those used for spectrophotometric assays. Some applications are described.

A dehydrogenase-mediated recycling system of NADPH in plant peroxisomes

The presence of the two NADP-dependent dehydrogenases of the pentose phosphate pathway has been investigated in plant peroxisomes from pea (Pisum sativum L.) leaves. Both enzymes, glucose-6-phosphate dehydrogenase (G6PDH; EC 1.1.1.49) and 6-phosphogluconate dehydrogenase (6PGDH; EC 1.1.1.44), were present in the matrix of leaf peroxisomes, and their kinetic properties were studied. G6PDH and 6PGDH showed a typical Michaelis-Menten kinetic saturation curve, and had specific activities of 12.4 and 29.6 mU/mg protein, respectively. The Km values of G6PDH and 6PGDH for glucose 6-phosphate and for 6-phosphogluconate were 107.3 and 10.2 microM, respectively. Dithiothreitol did not inhibit G6PDH activity. By isoelectric focusing of peroxisomal matrices, the G6PDH activity was resolved into three isoforms with isoelectric points of 5.55, 5.30 and 4.85. The isoelectric point of peroxisomal 6PGDH was 5.10. Immunoblot analyses of peroxisomal matrix with an antibody against yeast G6PDH revealed a single cross-reactive band of 56 kDa. Post-embedment, EM immunogold labelling of G6PDH confirmed that this enzyme was localized in the peroxisomal matrices, the thylakoid membrane and matrix of chloroplasts, and the cytosol. The presence of the two oxidative enzymes of the pentose phosphate pathway in plant peroxisomes implies that these organelles have the capacity to reduce NADP+ to NADPH for its re-utilization in the peroxisomal metabolism. NADPH is particularly required for the ascorbate-glutathione cycle, which has been recently demonstrated in plant peroxisomes [Jiménez, Hernández, del Río and Sevilla (1997) Plant Physiol. 114, 275-284] and represents an important antioxidant protection system against H2O2 generated in peroxisomes.