Heterogonous expression and characterization of a plant class IV chitinase from the pitcher of the carnivorous plant Nepenthes alata

Separation, purification and structural characterization of marine oligosaccharides: A comprehensive and systematic review of chromatographic methods

Marine oligosaccharides have now been applied in a wide range of industry due to various kinds of physiological activities. However, the oligosaccharides with different polymeric degrees (Dps) differed in physiological activities and applicable fields. So it is promising and essential to separate, purify and structurally characterize these oligosaccharides for understanding their structure-function relationship. This review will summarize the lasted developments in the separation, purification and structural characterization of marine oligosaccharides, including the alginate oligosaccharides, carrageenan oligosaccharides, agar oligosaccharides, chitin oligosaccharides and chitosan oligosaccharides, emphasizing the successful examples of methods for separation and purification. Furthermore, an outlook for preparation of functional oligosaccharides in food biotechnology and agriculture fields is also included. This comprehensive review could definitely promote the utilization of marine functional polysaccharides for food and agriculture.

Serine carboxypeptidases from the carnivorous plant Nepenthes mirabilis: Partial characterization and heterologous expression

This study aimed to partially characterize the three main serine carboxypeptidases (SCP3, SCP20, and SCP47) from Nepenthes mirabilis. Furthermore, one peptidase (SCP3) was chosen for further heterologous expression in Escherichia coli Shuffle®T7. SCP3 also was characterized in terms of its allergenic potential using bioinformatics tools. SCP3, SCP20, and SCP47 showed very similar 3D structures and mechanistic features to other plant serine peptidases belonging to clan SC and family S10. Although SCP3 was obtained in its soluble form, using 1% ethanol during induction with 0.5 mM IPTG at 16 °C for 18 h, it did not show proteolytic activity by zymography or in vitro analysis. SCP3 presented a few allergenic peptides and several cleavage sites for digestive enzymes. This work describes additional features of these enzymes, opening new perspectives for further studies for characterization and analysis of heterologous expression, as well as their potential biotechnological applications.

Enzyme activities in two sister-species of carnivorous pitcher plants (Nepenthes) with contrasting nutrient sequestration strategies

The carnivorous pitcher plants of the genus Nepenthes usually attract, capture and digest arthropod prey to obtain mineral nutrients. But few members of the genus have evolved specialized nutrient sequestration strategies to acquire nitrogen from the faeces and urine of mutualistic mammals, which they attract. Because the plants obtain significant amounts of nitrogen in a more available form, we hypothesized that they have relaxed the production of digestive enzymes. If so, species that digest mammal faeces should show fewer digestive enzymes than closely related species that rely on arthropods. We tested this hypothesis by comparing digestive enzymes in 1) Nepenthes hemsleyana, whose pitchers serve as roosts for the mutualistic woolly bat Kerivoula hardwickii, which also defecate inside the pitchers, and 2) the close relative Nepenthes rafflesiana, a typical arthropod capturing species. To investigate the dynamics of aspartic proteases (nepenthesin I and II) and type III and IV chitinases in both species, we conducted qPCR, western blotting, mass spectrometry, and enzyme activity measurements. We found that mRNA in pitcher tissue and enzyme abundance in the digestive fluid is upregulated in both species in response to faeces and insect feeding. Contrary to our initial hypothesis, the final nepenthesin proteolytic activity in the digestive fluid is higher in response to faeces addition than to insect prey irrespective of Nepenthes species. This indicates that faeces can mimic arthropod prey triggering the production of digestive enzymes and N. hemsleyana retained capacity for production of them.

Identification and Expression Analysis of Chitinase Genes in Pitchers of Nepenthes sp. during Development

Fifteen chitinases of classes I-V were identified in the transcriptomes of pitchers and adult leaves of the carnivorous plant Nepenthes sp. Ten of these chitinases were identified for the first time, including the chitinases of classes II and V. The expression levels of all found chitinase genes in leaves and at three stages of pitcher development were determined. The maximum level of transcriptional activity in an open pitcher was observed for the genes encoding chitinase NChi4 (class II) and its isoforms. The expression levels of these genes significantly increased as the pitcher developed. In addition, for the first time, transcription of the genes encoding chitinases of all five classes was detected in the leaves of this plant.

Chitinase: diversity, limitations, and trends in engineering for suitable applications

Chitinases catalyze the degradation of chitin, a ubiquitous polymer generated from the cell walls of fungi, shells of crustaceans, and cuticles of insects. They are gaining increasing attention in medicine, agriculture, food and drug industries, and environmental management. Their roles in the degradation of chitin for the production of industrially useful products and in the control of fungal pathogens and insect pests render them attractive for such purposes. However, chitinases have diverse sources, characteristics, and mechanisms of action that seem to restrain optimization procedures and render standardization techniques for enhanced practical applications complex. Hence, results of laboratory trials are not usually consistent with real-life applications. With the growing field of protein engineering, these complexities can be overcome by modifying or redesigning chitinases to enhance specific features required for specific applications. In this review, the variations in features and mechanisms of chitinases that limit their exploitation in biotechnological applications are compiled. Recent attempts to engineer chitinases for improved efficiency are also highlighted.

Regulation of enzyme activities in carnivorous pitcher plants of the genus Nepenthes

Nepenthes regulates enzyme activities by sensing stimuli from the insect prey. Protein is the best inductor mimicking the presence of an insect prey. Carnivorous plants of the genus Nepenthes have evolved passive pitcher traps for prey capture. In this study, we investigated the ability of chemical signals from a prey (chitin, protein, and ammonium) to induce transcription and synthesis of digestive enzymes in Nepenthes × Mixta. We used real-time PCR and specific antibodies generated against the aspartic proteases nepenthesins, and type III and type IV chitinases to investigate the induction of digestive enzyme synthesis in response to different chemical stimuli from the prey. Transcription of nepenthesins was strongly induced by ammonium, protein and live prey; chitin induced transcription only very slightly. This is in accordance with the amount of released enzyme and proteolytic activity in the digestive fluid. Although transcription of type III chitinase was induced by all investigated stimuli, a significant accumulation of the enzyme in the digestive fluid was found mainly after protein and live prey addition. Protein and live prey were also the best inducers for accumulation of type IV chitinase in the digestive fluid. Although ammonium strongly induced transcription of all investigated genes probably through membrane depolarization, strong acidification of the digestive fluid affected stability and abundance of both chitinases in the digestive fluid. The study showed that the proteins are universal inductors of enzyme activities in carnivorous pitcher plants best mimicking the presence of insect prey. This is not surprising, because proteins are a much valuable source of nitrogen, superior to chitin. Extensive vesicular activity was observed in prey-activated glands.

Structure and Enzymatic Properties of a Two-Domain Family GH19 Chitinase from Japanese Cedar ( Cryptomeria japonica) Pollen

CJP-4 is an allergen found in pollen of the Japanese cedar Cryptomeria japonica. The protein is a two-domain family GH19 (class IV) Chitinase consisting of an N-terminal CBM18 domain and a GH19 catalytic domain. Here, we produced recombinant CJP-4 and CBM18-truncated CJP-4 (CJP-4-Cat) proteins. In addition to solving the crystal structure of CJP-4-Cat by X-ray crystallography, we analyzed the ability of both proteins to hydrolyze chitin oligosaccharides, (GlcNAc) _n, polysaccharide substrates, glycol chitin, and β-chitin nanofiber and examined their inhibitory activity toward fungal growth. Truncation of the CBM18 domain did not significantly affect the mode of (GlcNAc) _n hydrolysis. However, significant effects were observed when we used the polysaccharide substrates. The activity of CJP-4 toward the soluble substrate, glycol chitin, was lower than that of CJP-4-Cat. In contrast, CJP-4 exhibited higher activity toward β-chitin nanofiber, an insoluble substrate, than did CJP-4-Cat. Fungal growth was strongly inhibited by CJP-4 but not by CJP-4-Cat. These results indicate that the CBM18 domain assists the hydrolysis of insoluble substrate and the antifungal action of CJP-4-Cat by binding to chitin. CJP-4-Cat was found to have only two loops (loops I and III), as reported for ChiA, an allergenic class IV Chitinase from maize.

Discovery of digestive enzymes in carnivorous plants with focus on proteases

BACKGROUND

Carnivorous plants have been fascinating researchers with their unique characters and bioinspired applications. These include medicinal trait of some carnivorous plants with potentials for pharmaceutical industry.

METHODS

This review will cover recent progress based on current studies on digestive enzymes secreted by different genera of carnivorous plants: Drosera (sundews), Dionaea (Venus flytrap), Nepenthes (tropical pitcher plants), Sarracenia (North American pitcher plants), Cephalotus (Australian pitcher plants), Genlisea (corkscrew plants), and Utricularia (bladderworts).

RESULTS

Since the discovery of secreted protease nepenthesin in Nepenthes pitcher, digestive enzymes from carnivorous plants have been the focus of many studies. Recent genomics approaches have accelerated digestive enzyme discovery. Furthermore, the advancement in recombinant technology and protein purification helped in the identification and characterisation of enzymes in carnivorous plants.

DISCUSSION

These different aspects will be described and discussed in this review with focus on the role of secreted plant proteases and their potential industrial applications.

Characterization of a Bacillus thuringiensis chitinase that binds to cellulose and chitin

Bacillus thuringiensis is a Gram-positive soil bacterium that is known to be a bacterial biopesticide that produces insecticidal proteins called crystal proteins (Cry). In the insecticidal process, chitinases are suggested to perforate the peritrophic membrane barrier to facilitate the invasion of the Cry proteins into epithelial membranes. A chitinase gene from B. thuringiensis was successfully expressed in a soluble form in Escherichia coli, and the gene product was purified and characterized. The purified recombinant enzyme, BthChi74, hydrolyzed an artificial substrate, 4-nitrophenyl N,N′-diacetyl-β-d-chitobioside [4NP-(GlcNAc)₂], and the natural substrates, colloidal chitin and crystalline α-chitin, but it did not hydrolyze cellulose. BthChi74 exhibited catalytic activity under a weakly acidic to neutral pH range at 50 °C, and it was stable over a wide pH range for 24 h. Differential scanning fluorimetry (DSF) indicated a protein melting temperature (T_m) of 63.6 °C. Kinetic analysis revealed k_cat and K_M values of 1.5 s⁻¹ and 159 μM, respectively, with 4NP-(GlcNAc)₂ as a substrate. BthChi74 produced (GlcNAc)₂ and GlcNAc from colloidal chitin and α-chitin as substrates, but the activity toward the latter was lower than that toward the former. BthChi74 could bind similarly to chitin beads, crystalline α-chitin, and cellulose through a unique family 2 carbohydrate-binding module (CBM2). The structure–function relationships of BthChi74 are discussed in relation to other chitinases, such as Listeria chitinase, which possesses a family 5 carbohydrate-binding module (CBM5).

Structure prediction and network analysis of chitinases from the Cape sundew, Drosera capensis

BACKGROUND

Carnivorous plants possess diverse sets of enzymes with novel functionalities applicable to biotechnology, proteomics, and bioanalytical research. Chitinases constitute an important class of such enzymes, with future applications including human-safe antifungal agents and pesticides. Here, we compare chitinases from the genome of the carnivorous plant Drosera capensis to those from related carnivorous plants and model organisms.

METHODS

Using comparative modeling, in silico maturation, and molecular dynamics simulation, we produce models of the mature enzymes in aqueous solution. We utilize network analytic techniques to identify similarities and differences in chitinase topology.

RESULTS

Here, we report molecular models and functional predictions from protein structure networks for eleven new chitinases from D. capensis, including a novel class IV chitinase with two active domains. This architecture has previously been observed in microorganisms but not in plants. We use a combination of comparative and de novo structure prediction followed by molecular dynamics simulation to produce models of the mature forms of these proteins in aqueous solution. Protein structure network analysis of these and other plant chitinases reveal characteristic features of the two major chitinase families.

GENERAL SIGNIFICANCE

This work demonstrates how computational techniques can facilitate quickly moving from raw sequence data to refined structural models and comparative analysis, and to select promising candidates for subsequent biochemical characterization. This capability is increasingly important given the large and growing body of data from high-throughput genome sequencing, which makes experimental characterization of every target impractical.

The role of electrical and jasmonate signalling in the recognition of captured prey in the carnivorous sundew plant Drosera capensis

The carnivorous sundew plant (Drosera capensis) captures prey using sticky tentacles. We investigated the tentacle and trap reactions in response to the electrical and jasmonate signalling evoked by different stimuli to reveal how carnivorous sundews recognize digestible captured prey in their traps. We measured the electrical signals, phytohormone concentration, enzyme activities and Chla fluorescence in response to mechanical stimulation, wounding or insect feeding in local and systemic traps. Seven new proteins in the digestive fluid were identified using mass spectrometry. Mechanical stimuli and live prey induced a fast, localized tentacle-bending reaction and enzyme secretion at the place of application. By contrast, repeated wounding induced a nonlocalized convulsive tentacle movement and enzyme secretion in local but also in distant systemic traps. These differences can be explained in terms of the electrical signal propagation and jasmonate accumulation, which also had a significant impact on the photosynthesis in the traps. The electrical signals generated in response to wounding could partially mimic a mechanical stimulation of struggling prey and might trigger a false alarm, confirming that the botanical carnivory and plant defence mechanisms are related. To trigger the full enzyme activity, the traps must detect chemical stimuli from the captured prey.

Structural and functional characterisation of a class I endochitinase of the carnivorous sundew (Drosera rotundifolia L.)

Chitinase gene from the carnivorous plant, Drosera rotundifolia , was cloned and functionally characterised. Plant chitinases are believed to play an important role in the developmental and physiological processes and in responses to biotic and abiotic stress. In addition, there is growing evidence that carnivorous plants can use them to digest insect prey. In this study, a full-length genomic clone consisting of the 1665-bp chitinase gene (gDrChit) and adjacent promoter region of the 698 bp in length were isolated from Drosera rotundifolia L. using degenerate PCR and a genome-walking approach. The corresponding coding sequence of chitinase gene (DrChit) was obtained following RNA isolation from the leaves of aseptically grown in vitro plants, cDNA synthesis with a gene-specific primer and PCR amplification. The open reading frame of cDNA clone consisted of 978 nucleotides and encoded 325 amino acid residues. Sequence analysis indicated that DrChit belongs to the class I group of plant chitinases. Phylogenetic analysis within the Caryophyllales class I chitinases demonstrated a significant evolutionary relatedness of DrChit with clade Ib, which contains the extracellular orthologues that play a role in carnivory. Comparative expression analysis revealed that the DrChit is expressed predominantly in tentacles and is up-regulated by treatment with inducers that mimick insect prey. Enzymatic activity of rDrChit protein expressed in Escherichia coli was confirmed and purified protein exhibited a long oligomer-specific endochitinase activity on glycol-chitin and FITC-chitin. The isolation and expression profile of a chitinase gene from D. rotundifolia has not been reported so far. The obtained results support the role of specific chitinases in digestive processes in carnivorous plant species.

Addressing proteolytic efficiency in enzymatic degradation therapy for celiac disease

Celiac disease is triggered by partially digested gluten proteins. Enzyme therapies that complete protein digestion in vivo could support a gluten-free diet, but the barrier to completeness is high. Current options require enzyme amounts on the same order as the protein meal itself. In this study, we evaluated proteolytic components of the carnivorous pitcher plant (Nepenthes spp.) for use in this context. Remarkably low doses enhance gliadin solubilization rates, and degrade gliadin slurries within the pH and temporal constraints of human gastric digestion. Potencies in excess of 1200:1 (substrate-to-enzyme) are achieved. Digestion generates small peptides through nepenthesin and neprosin, the latter a novel enzyme defining a previously-unknown class of prolyl endoprotease. The digests also exhibit reduced TG2 conversion rates in the immunogenic regions of gliadin, providing a twin mechanism for evading T-cell recognition. When sensitized and dosed with enzyme-treated gliadin, NOD/DQ8 mice did not show intestinal inflammation, when compared to mice challenged with only pepsin-treated gliadin. The low enzyme load needed for effective digestion suggests that gluten detoxification can be achieved in a meal setting, using metered dosing based on meal size. We demonstrate this by showing efficient antigen processing at total substrate-to-enzyme ratios exceeding 12,000:1.

Carnivorous Nutrition in Pitcher Plants (Nepenthes spp.) via an Unusual Complement of Endogenous Enzymes

Plants belonging to the genus Nepenthes are carnivorous, using specialized pitfall traps called "pitchers" that attract, capture, and digest insects as a primary source of nutrients. We have used RNA sequencing to generate a cDNA library from the Nepenthes pitchers and applied it to mass spectrometry-based identification of the enzymes secreted into the pitcher fluid using a nonspecific digestion strategy superior to trypsin in this application. This first complete catalog of the pitcher fluid subproteome includes enzymes across a variety of functional classes. The most abundant proteins present in the secreted fluid are proteases, nucleases, peroxidases, chitinases, a phosphatase, and a glucanase. Nitrogen recovery involves a particularly rich complement of proteases. In addition to the two expected aspartic proteases, we discovered three novel nepenthensins, two prolyl endopeptidases that we name neprosins, and a putative serine carboxypeptidase. Additional proteins identified are relevant to pathogen-defense and secretion mechanisms. The full complement of acid-stable enzymes discovered in this study suggests that carnivory in the genus Nepenthes can be sustained by plant-based mechanisms alone and does not absolutely require bacterial symbiosis.

Characterization of two Listeria innocua chitinases of different sizes that were expressed in Escherichia coli

Two putative chitinase genes, lin0153 and lin1996, from the nonpathogenic bacterium Listeria innocua were expressed in Escherichia coli, and the gene products were characterized. The genes were close homologs of chitinases from the pathogenic bacterium Listeria monocytogenes, in which chitinases and chitin-binding proteins play important roles in pathogenesis in mice-infection models. The purified recombinant enzymes that are different in size, LinChi78 (lin0153 product) and LinChi35 (lin1996 product)-with molecular masses of 82 and 38 kDa, including vector-derived additional sequences, respectively-exhibited optimum catalytic activity under neutral and acidic conditions at 50 °C, respectively, and were stable over broad pH (4-11) and temperature (4-40 °C) ranges. LinChi35 displayed higher k cat and K M values for 4-nitrophenyl N,N-diacetyl-β-D-chitobioside [4NP-(GlcNAc)2] than LinChi78. Both enzymes produced primarily dimers from colloidal chitin as a substrate. However, LinChi78 and LinChi35 could hydrolyze oligomeric substrates in a processive exo- and nonprocessive endo-manner, respectively, and showed different reactivity toward oligomeric substrates. Both enzymes could bind chitin beads but were different in their binding ability toward crystalline α-chitin and cellulose. The structure-function relationships of these chitinases are discussed in reference to other bacterial chitinases.

Proteome analysis of digestive fluids in Nepenthes pitchers

BACKGROUND AND AIMS

Carnivorous plants have developed strategies to enable growth in nutrient-poor soils. For the genus Nepenthes, this strategy represents producing pitcher-modified leaves that can trap and digest various prey. These pitchers produce a digestive fluid composed of proteins, including hydrolytic enzymes. The focus of this study was on the identification of these proteins.

METHODS

In order to better characterize and have an overview of these proteins, digestive fluid was sampled from pitchers at different stages of maturity from five species of Nepenthes (N. mirabilis, N. alata, N. sanguinea, N. bicalcarata and N. albomarginata) that vary in their ecological niches and grew under different conditions. Three complementary approaches based on transcriptomic resources, mass spectrometry and in silico analysis were used.

KEY RESULTS

This study permitted the identification of 29 proteins excreted in the pitchers. Twenty of these proteins were never reported in Nepenthes previously and included serine carboxypeptidases, α- and β-galactosidases, lipid transfer proteins and esterases/lipases. These 20 proteins display sequence signals allowing their secretion into the pitcher fluid.

CONCLUSIONS

Nepenthes pitcher plants have evolved an arsenal of enzymes to digest prey caught in their traps. The panel of new proteins identified in this study provides new insights into the digestive process of these carnivorous plants.

Microbiome and Biocatalytic Bacteria in Monkey Cup (Nepenthes Pitcher) Digestive Fluid

Tropical carnivorous plant, Nepenthes, locally known as “monkey cup”, utilises its pitcher as a passive trap to capture insects. It then secretes enzymes into the pitcher fluid to digest the insects for nutrients acquisition. However, little is known about the microbiota and their activity in its pitcher fluid. Eighteen bacteria phyla were detected from the metagenome study in the Nepenthes pitcher fluid. Proteobacteria, Bacteroidetes and Actinobacteria are the dominant phyla in the Nepenthes pitcher fluid. We also performed culturomics approach by isolating 18 bacteria from the Nepenthes pitcher fluid. Most of the bacterial isolates possess chitinolytic, proteolytic, amylolytic, and cellulolytic and xylanolytic activities. Fifteen putative chitinase genes were identified from the whole genome analysis on the genomes of the 18 bacteria isolated from Nepenthes pitcher fluid and expressed for chitinase assay. Of these, six clones possessed chitinase activity. In conclusion, our metagenome result shows that the Nepenthes pitcher fluid contains vast bacterial diversity and the culturomic studies confirmed the presence of biocatalytic bacteria within the Nepenthes pitcher juice which may act in symbiosis for the turn over of insects trapped in the Nepenthes pitcher fluid.

A simple SDS-PAGE protein pattern from pitcher secretions as a new tool to distinguish Nepenthes species (Nepenthaceae)

PREMISE OF THE STUDY

Carnivorous plants have always fascinated scientists because these plants are able to attract, capture, and digest animal prey using their remarkable traps that contain digestive secretions. Nepenthes is one of the largest genera of carnivorous plants, with 120 species described thus far. Despite an outstanding diversity of trap designs, many species are often confused with each other and remain difficult to classify because they resemble pitchers or of the occurrence of interspecific hybrids.

METHODS

Here, we propose a new method to easily distinguish Nepenthes species based on a SDS PAGE protein pattern analysis of their pitcher secretions. Intraspecific comparisons were performed among specimens growing in different environmental conditions to ascertain the robustness of this method.

KEY RESULTS

Our results show that, at the juvenile stage and in the absence of prey in the pitcher, an examined species is characterized by a specific and stable profile, whatever the environmental conditions.

CONCLUSIONS

The method we describe here can be used as a reliable tool to easily distinguish between Nepenthes species and to help with potential identification based on the species-specific protein pattern of their pitcher secretions, which is complementary to the monograph information.

Glucan-rich diet is digested and taken up by the carnivorous sundew (Drosera rotundifolia L.): implication for a novel role of plant β-1,3-glucanases

Carnivory in plants evolved as an adaptation strategy to nutrient-poor environments. Thanks to specialized traps, carnivorous plants can gain nutrients from various heterotrophic sources such as small insects. Digestion in traps requires a coordinated action of several hydrolytic enzymes that break down complex substances into simple absorbable nutrients. Among these, several pathogenesis-related proteins including β-1,3-glucanases have previously been identified in digestive fluid of some carnivorous species. Here we show that a single acidic endo-β-1,3-glucanase of ~50 kDa is present in the digestive fluid of the flypaper-trapped sundew (Drosera rotundifolia L.). The enzyme is inducible with a complex plant β-glucan laminarin from which it releases simple saccharides when supplied to leaves as a substrate. Moreover, thin-layer chromatography of digestive exudates showed that the simplest degradation products (especially glucose) are taken up by the leaves. These results for the first time point on involvement of β-1,3-glucanases in digestion of carnivorous plants and demonstrate the uptake of saccharide-based compounds by traps. Such a strategy could enable the plant to utilize other types of nutritional sources e.g., pollen grains, fungal spores or detritus from environment. Possible multiple roles of β-1,3-glucanases in the digestive fluid of carnivorous sundew are also discussed.

Transgenic expression of plant chitinases to enhance disease resistance

Crop plants have evolved an array of mechanisms to counter biotic and abiotic stresses. Many pathogenesis-related proteins are expressed by plants during the attack of pathogens. Advances in recombinant DNA technology and understanding of plant-microbe interactions at the molecular level have paved the way for isolation and characterization of genes encoding such proteins, including chitinases. Chitinases are included in families 18 and 19 of glycosyl hydrolases (according to www.cazy.org ) and they are further categorized into seven major classes based on their aminoacid sequence homology, three-dimensional structures, and hydrolytic mechanisms of catalytic reactions. Although chitin is not a component of plant cell walls, plant chitinases are involved in development and non-specific stress responses. Also, chitinase genes sourced from plants have been successfully over-expressed in crop plants to combat fungal pathogens. Crops such as tomato, potato, maize, groundnut, mustard, finger millet, cotton, lychee, banana, grape, wheat and rice have been successfully engineered for fungal resistance either with chitinase alone or in combination with other PR proteins.

Biochemical characterization of a recombinant plant class III chitinase from the pitcher of the carnivorous plant Nepenthes alata

A class III chitinase belonging to the GH18 family from Nepenthes alata (NaCHIT3) was expressed in Escherichia coli. The enzyme exhibited hydrolytic activity toward colloidal chitin, ethylene glycol chitin, and (GlcNAc)(n) (n=5 and 6). The enzyme hydrolyzed the fourth glycosidic linkage from the non-reducing end of (GlcNAc)(6). The anomeric form of the products indicated it was a retaining enzyme. The colloidal chitin hydrolytic reaction displayed high activity between pH 3.9 and 6.9, but the pH optimum of the (GlcNAc)(6) hydrolytic reaction was 3.9 at 37 °C. The optimal temperature for activity was 65 °C in 50 mM sodium acetate buffer (pH 3.9). The pH optima of NaCHIT3 and NaCHIT1 might be related to their roles in chitin degradation in the pitcher fluid.

Proteomic analysis of secreted protein induced by a component of prey in pitcher fluid of the carnivorous plant Nepenthes alata

The Nepenthes species are carnivorous plants that have evolved a specialized leaf organ, the 'pitcher', to attract, capture, and digest insects. The digested insects provide nutrients for growth, allowing these plants to grow even in poor soil. Several proteins have been identified in the pitcher fluid, including aspartic proteases (nepenthesin I and II) and pathogenesis-related (PR) proteins (β-1,3-glucanase, class IV chitinase, and thaumatin-like protein). In this study, we collected and concentrated pitcher fluid to identify minor proteins. In addition, we tried to identify the protein secreted in response to trapping the insect. To make a similar situation in which the insect falls into the pitcher, chitin which was a major component of the insect exoskeleton was added to the fluid in the pitcher. Three PR proteins, class III peroxidase (Prx), β-1,3-glucanase, and class III chitinase, were newly identified. Prx was induced after the addition of chitin to the pitcher fluid. Proteins in the pitcher fluid of the carnivorous plant Nepenthes alata probably have two roles in nutrient supply: digestion of prey and the antibacterial effect. These results suggest that the system for digesting prey has evolved from the defense system against pathogens in the carnivorous plant Nepenthes.