Characterization of a novel Kazal-type serine proteinase inhibitor of Arabidopsis thaliana

Functional characterization of novel RbTI gene from ricebean and validation of its insecticidal properties in transgenic tobacco

Plant protease inhibitors (PI's) inhibit the activity of gut proteases and thus provide resistance against insect attack. Previously we have published first report on cloning and characterization of a novel Bowman-Birk protease inhibitor gene (RbTI) from ricebean (Vigna umbellata). In this study, the RbTI gene was further characterized and validated as a potential candidate for transferring insect resistance in economically important crops. We have successfully generated transgenic tobacco plants expressing RbTI gene constitutively under CaMV35S promoter using Agrobacterium transformation. Genomic PCR and GUS analysis confirmed the successful integration of RbTI gene into tobacco plant genome. qRT-PCR analysis revealed highest RbTI gene expression in transformed tobacco leaves nearing maturity. Feeding of transformed tobacco leaf tissue showed prominent effect on larval mortality throughout the larval growth stages mainly during first three days of feeding. For functional analysis of RbTI gene, we estimated the inhibitory activity of protein extracts from normal and transformed tobacco plants against gut proteases of Spodoptera litura and H. armigera larval instars. Maximum inhibition of trypsin (82.42% and 73.25%) and chymotrypsin (69.50% and 60.64%) enzymes was recorded at early larval stages of both insects. The results of this study validated the future use of RbTI gene from ricebean legume as a potential candidate for transferring insect resistance in economically important crops. Insight, innovation, integration: Present study was conducted with the aim to utilize the state of art biotechnological techniques for transferring key pest resistant genes from underutilized promising crop ricebean. The tobacco plant has been utilized as modern plant for proof of concept where a protease inhibitor gene from Ricebean has been transferred to tobacco plant which induced larval mortality within first three days of feeding at all larval developmental stages. The biochemical assays on mid-gut total protein extract showed that the transgenic tobacco leaves have inhibiting effect on trypsin and chymotrypsin enzymes of insect which is otherwise required for digestion of food by them. Hence, we provide a novel gene that could be utilized for pest resistance in other crops different developmental stages.

Plant Kunitz Inhibitors and Their Interaction with Proteases: Current and Potential Pharmacological Targets

The action of proteases can be controlled by several mechanisms, including regulation through gene expression; post-translational modifications, such as glycosylation; zymogen activation; targeting specific compartments, such as lysosomes and mitochondria; and blocking proteolysis using endogenous inhibitors. Protease inhibitors are important molecules to be explored for the control of proteolytic processes in organisms because of their ability to act on several proteases. In this context, plants synthesize numerous proteins that contribute to protection against attacks by microorganisms (fungi and bacteria) and/or invertebrates (insects and nematodes) through the inhibition of proteases in these organisms. These proteins are widely distributed in the plant kingdom, and are present in higher concentrations in legume seeds (compared to other organs and other botanical families), motivating studies on their inhibitory effects in various organisms, including humans. In most cases, the biological roles of these proteins have been assigned based mostly on their in vitro action, as is the case with enzyme inhibitors. This review highlights the structural evolution, function, and wide variety of effects of plant Kunitz protease inhibitors, and their potential for pharmaceutical application based on their interactions with different proteases.

Potent antibacterial and antibiofilm activities of TICbf-14, a peptide with increased stability against trypsin

The poor stability of peptides against trypsin largely limits their development as potential antibacterial agents. Here, to obtain a peptide with increased trypsin stability and potent antibacterial activity, TICbf-14 derived from the cationic peptide Cbf-14 was designed by the addition of disulfide-bridged hendecapeptide (CWTKSIPPKPC) loop. Subsequently, the trypsin stability and antimicrobial and antibiofilm activities of this peptide were evaluated. The possible mechanisms underlying its mode of action were also clarified. The results showed that TICbf-14 exhibited elevated trypsin inhibitory activity and effectively mitigated lung histopathological damage in bacteria-infected mice by reducing the bacterial counts, further inhibiting the systemic dissemination of bacteria and host inflammation. Additionally, TICbf-14 significantly repressed bacterial swimming motility and notably inhibited biofilm formation. Considering the mode of action, we observed that TICbf-14 exhibited a potent membrane-disruptive mechanism, which was attributable to its destructive effect on ionic bridges between divalent cations and LPS of the bacterial membrane. Overall, TICbf-14, a bifunctional peptide with both antimicrobial and trypsin inhibitory activity, is highly likely to become an ideal candidate for drug development against bacteria.

Antimicrobial peptides in the seedling transcriptome of the tree legume Peltophorum dubium

Antimicrobial peptides (AMPs) play an essential role in plant defense against invading pathogens. Due to their biological properties, these molecules have been considered useful for drug development, as novel agents in disease therapeutics, applicable to both agriculture and medicine. New technologies of massive sequencing open opportunities to discover novel AMP encoding genes in wild plant species. This work aimed to identify cysteine-rich AMPs from Peltophorum dubium, a legume tree from South America. We performed whole-transcriptome sequencing of P. dubium seedlings followed by de novo transcriptome assembly, uncovering 78 AMP transcripts classified into five families: hevein-like, lipid-transfer proteins (LTPs), alpha hairpinins, defensins, and snakin/GASA (Giberellic Acid Stimulated in Arabidopsis) peptides. No transcripts with similarity to cyclotide or thionin genes were identified. Genomic DNA analysis by PCR confirmed the presence of 18 genes encoding six putative defensins and 12 snakin/GASA peptides and allowed the characterization of their exon-intron structure. The present work demonstrates that AMP prediction from a wild species is possible using RNA sequencing and de novo transcriptome assembly, regarding a starting point for studies focused on AMP gene evolution and expression. Moreover, this study allowed the detection of strong AMP candidates for drug development and novel biotechnological products.

Transcriptome analysis and functional validation reveal a novel gene, BcCGF1, that enhances fungal virulence by promoting infection-related development and host penetration

Simultaneous transcriptome analyses of both host plants and pathogens, and functional validation of the identified differentially expressed genes (DEGs) allow us to better understand the mechanisms underlying their interactions. Here, we analyse the mixed transcriptome derived from Botrytis cinerea (the causal agent of grey mould) infected tomato leaves at 24 hr after inoculation, a critical time point at which the pathogen has penetrated and developed in the leaf epidermis, whereas necrotic symptoms have not yet appeared. Our analyses identified a complex network of genes involved in the tomato-B. cinerea interaction. The expression of fungal transcripts encoding candidate effectors, enzymes for secondary metabolite biosynthesis, hormone and reactive oxygen species (ROS) production, and autophagy-related proteins was up-regulated, suggesting that these genes may be involved in the initial infection processes. Specifically, tomato genes involved in phytoalexin production, stress responses, ATP-binding cassette transporters, pathogenesis-related proteins, and WRKY DNA-binding transcription factors were up-regulated. We functionally investigated several B. cinerea DEGs via gene replacement and pathogenicity assays, and demonstrated that BcCGF1 was a novel virulence-associated factor that mediates fungal development and virulence via regulation of conidial germination, conidiation, infection structure formation, host penetration, and stress adaptation. The fungal infection-related development was controlled by BcCGF-mediated ROS production and exogenous cAMP restored the mutant infection-related development. Our findings provide new insights into the elucidation of the simultaneous tactics of pathogen attack and host defence. Our systematic elucidation of BcCGF1 in mediating fungal pathogenesis may open up new targets for fungal disease control.

Heat treatment alleviates the growth and photosynthetic impairment of transplastomic plants expressing Leishmania infantum Hsp83-Toxoplasma gondii SAG1 fusion protein

Previously, we showed that transplastomic tobacco plants expressing the LiHsp83-SAG1 fusion protein displayed a chlorotic phenotype and growth retardation, while plants expressing the SAG1 and GRA4 antigens alone did not. We conducted a comprehensive examination of the metabolic and photosynthetic parameters that could be affecting the normal growth of LiHsp83-SAG1 plants in order to understand the origin of these pleiotropic effects. These plants presented all photosynthetic pigments and parameters related to PSII efficiency significantly diminished. However, the expression of CHLI, RSSU and LHCa/b genes did not show significant differences between LiHsp83-SAG1 and control plants. Total protein, starch, and soluble sugar contents were also greatly reduced in LiHsp83-SAG1 plants. Since Hsp90 s are constitutively expressed at much higher concentrations at high temperatures, we tested if the fitness of LiHsp83-SAG1 over-expressing LiHsp83 would improve after heat treatment. LiHsp83-SAG1 plants showed an important alleviation of their phenotype and an evident recovery of the PSII function. As far as we know, this is the first report where it is demonstrated that a transplastomic line performs much better at higher temperatures. Finally, we detected that LiHsp83-SAG1 protein could be binding to key photosynthesis-related proteins at 37 °C. Our results suggest that the excess of this molecular chaperone could benefit the plant in a possible heat shock and prevent the expected denaturation of proteins. However, the LiHsp83-SAG1 protein content was weakly decreased in heat-treated plants. Therefore, we cannot rule out that the alleviation observed at 37 °C may be partially due to a reduction of the levels of the recombinant protein.

Plant Serine Protease Inhibitors: Biotechnology Application in Agriculture and Molecular Farming

The serine protease inhibitors (SPIs) are widely distributed in living organisms like bacteria, fungi, plants, and humans. The main function of SPIs as protease enzymes is to regulate the proteolytic activity. In plants, most of the studies of SPIs have been focused on their physiological role. The initial studies carried out in plants showed that SPIs participate in the regulation of endogenous proteolytic processes, as the regulation of proteases in seeds. Besides, it was observed that SPIs also participate in the regulation of cell death during plant development and senescence. On the other hand, plant SPIs have an important role in plant defense against pests and phytopathogenic microorganisms. In the last 20 years, several transgenic plants over-expressing SPIs have been produced and tested in order to achieve the increase of the resistance against pathogenic insects. Finally, in molecular farming, SPIs have been employed to minimize the proteolysis of recombinant proteins expressed in plants. The present review discusses the potential biotechnological applications of plant SPIs in the agriculture field.

Crystal structure of the WFIKKN2 follistatin domain reveals insight into how it inhibits growth differentiation factor 8 (GDF8) and GDF11

Growth differentiation factor 8 (GDF8; also known as myostatin) and GDF11 are closely related members of the transforming growth factor β (TGF-β) family. GDF8 strongly and negatively regulates skeletal muscle growth, and GDF11 has been implicated in various age-related pathologies such as cardiac hypertrophy. GDF8 and GDF11 signaling activities are controlled by the extracellular protein antagonists follistatin; follistatin-like 3 (FSTL3); and WAP, follistatin/kazal, immunoglobulin, Kunitz, and netrin domain-containing (WFIKKN). All of these proteins contain a follistatin domain (FSD) important for ligand binding and antagonism. Here, we investigated the structure and function of the FSD from murine WFIKKN2 and compared it with the FSDs of follistatin and FSTL3. Using native gel shift and surface plasmon resonance analyses, we determined that the WFIKKN2 FSD can interact with both GDF8 and GDF11 and block their interactions with the type II receptor activin A receptor type 2B (ActRIIB). Further, we solved the crystal structure of the WFIKKN2 FSD to 1.39 Å resolution and identified surface-exposed residues that, when substituted with alanine, reduce antagonism of GDF8 in full-length WFIKKN2. Comparison of the WFIKKN2 FSD with those of follistatin and FSTL3 revealed differences in both the FSD structure and position of residues within the domain that are important for ligand antagonism. Taken together, our results indicate that both WFIKKN and follistatin utilize their FSDs to block the type II receptor but do so via different binding interactions.

Glycosylphosphatidylinositol-Anchored Proteins in Arabidopsis and One of Their Common Roles in Signaling Transduction

Diverse proteins are found modified with glycosylphosphatidylinositol (GPI) at their carboxyl terminus in eukaryotes, which allows them to associate with membrane lipid bilayers and anchor on the external surface of the plasma membrane. GPI-anchored proteins (GPI-APs) play crucial roles in various processes, and more and more GPI-APs have been identified and studied. In this review, previous genomic and proteomic predictions of GPI-APs in Arabidopsis have been updated, which reveal their high abundance and complexity. From studies of individual GPI-APs in Arabidopsis, certain GPI-APs have been found associated with partner receptor-like kinases (RLKs), targeting RLKs to their subcellular localization and helping to recognize extracellular signaling polypeptide ligands. Interestingly, the association might also be involved in ligand selection. The analyses suggest that GPI-APs are essential and widely involved in signal transduction through association with RLKs.

From structure to function - a family portrait of plant subtilases

Contents Summary 901 I. Introduction 901 II. Biochemistry and structure of plant SBTs 902 III. Phylogeny of plant SBTs and family organization 903 IV. Physiological roles of plant SBTs 905 V. Conclusions and outlook 911 Acknowledgements 912 References 912 SUMMARY: Subtilases (SBTs) are serine peptidases that are found in all three domains of life. As compared with homologs in other Eucarya, plant SBTs are more closely related to archaeal and bacterial SBTs, with which they share many biochemical and structural features. However, in the course of evolution, functional diversification led to the acquisition of novel, plant-specific functions, resulting in the present-day complexity of the plant SBT family. SBTs are much more numerous in plants than in any other organism, and include enzymes involved in general proteolysis as well as highly specific processing proteases. Most SBTs are targeted to the cell wall, where they contribute to the control of growth and development by regulating the properties of the cell wall and the activity of extracellular signaling molecules. Plant SBTs affect all stages of the life cycle as they contribute to embryogenesis, seed development and germination, cuticle formation and epidermal patterning, vascular development, programmed cell death, organ abscission, senescence, and plant responses to their biotic and abiotic environments. In this article we provide a comprehensive picture of SBT structure and function in plants.

Toxoplasma gondii serine-protease inhibitor-1: A new adjuvant candidate for asthma therapy

Serine-proteases are important players in the pathogenesis of asthma, promoting inflammation and tissue remodeling. It’s also known that many serine protease inhibitors display immunomodulatory properties. TgPI-1 is a Toxoplasma gondii protein that exhibits broad spectrum inhibitory activity against serine proteases. In view of the increased prevalence of atopic disorders and the need to develop new treatment strategies we sought to investigate the potential of TgPI-1 for treating respiratory allergies. For this purpose, we developed a therapeutic experimental model. BALB/c mice were rendered allergic by intraperitoneal ovalbumin-alum sensitization and airway-challenged. Once the asthmatic phenotype was achieved, mice were intranasally treated with rTgPI-1 alone or with a mixture of rTgPI-1 and ovalbumin (OVA). A week later mice were given a secondary aerosol challenge. Treatment with rTgPI-1 alone or co-administered with OVA diminished bronchoalveolar eosinophilia, mucus production and peribronchial lung infiltration. This effect was accompanied by a lung resistance reduction of 26.3% and 50.3% respectively. Both treatments resulted in the production of lower levels of IL-4, IL-5, IFN-γ and regulatory IL-10 by thoracic lymph node cells stimulated with OVA. Interestingly, significant decreases in OVA specific IgE and T cell proliferation, and increases in FoxP3⁺ T cells at local and systemic levels were only detected when the inhibitor was administered along with OVA. These results show that both rTgPI-1 treatments reduced asthma hallmarks. However, co-administration of the inhibitor with the allergen was more effective. Hence, rTgPI-1 emerges as a novel adjuvant candidate for asthma treatment.

Purification and Characterization of a Novel Kazal-Type Trypsin Inhibitor from the Leech of Hirudinaria manillensis

Kazal-type serine proteinase inhibitors are found in a large number of living organisms and play crucial roles in various biological and physiological processes. Although some Kazal-type serine protease inhibitors have been identified in leeches, none has been reported from Hirudinaria manillensis, which is a medically important leech. In this study, a novel Kazal-type trypsin inhibitor was isolated from leech H. manillensis, purified and named as bdellin-HM based on the sequence similarity with bdellin-KL and bdellin B-3. Structural analysis revealed that bdellin-HM was a 17,432.8 Da protein and comprised of 149 amino acid residues with six cysteines forming three intra-molecular disulfide bonds. Bdellin-HM showed similarity with the Kazal-type domain and may belong to the group of “non-classical” Kazal inhibitors according to its Cys^I-Cys^II disulfide bridge position. Bdellin-HM had no inhibitory effect on elastase, chymotrypsin, kallikrein, Factor (F) XIIa, FXIa, FXa, thrombin and plasmin, but it showed a potent ability to inhibit trypsin with an inhibition constant (K_i) of (8.12 ± 0.18) × 10⁻⁹ M. These results suggest that bdellin-HM from the leech of H. manillensis plays a potent and specific inhibitory role towards trypsin.