Substrate specificity of human chymotrypsin-like protease (CTRL) characterized by phage display-selected small-protein inhibitors

Chymotrypsin-like protease (CTRL) is one of the four chymotrypsin isoforms expressed in the human exocrine pancreas. Human genetic and experimental evidence indicate that chymotrypsins B1, B2, and C (CTRB1, CTRB2 and CTRC) are important not only for protein digestion but also for protecting the pancreas against pancreatitis by degrading potentially harmful trypsinogen. CTRL has not been reported to play a similar role, possibly due to its low abundance and/or different substrate specificity. To address this problem, we investigated the specificity of the substrate-binding groove of CTRL by evolving the substrate-like canonical loop of the Schistocerca gregaria proteinase inhibitor 2 (SGPI-2), a small-protein reversible chymotrypsin inhibitor to bind CTRL. We found that phage-associated SGPI-2 variants with strong affinity to CTRL were similar to those evolved previously against CTRB1, CTRB2 or bovine chymotrypsin A (bCTRA), indicating comparable substrate specificity. When tested as recombinant proteins, SGPI-2 variants inhibited CTRL with similar or slightly weaker affinity than bCTRA, confirming that CTRL is a typical chymotrypsin. Interestingly, an SGPI-2 variant selected with a Thr29His mutation in its reactive loop was found to inhibit CTRL strongly, but it was digested rapidly by bCTRA. Finally, CTRL was shown to degrade human anionic trypsinogen, however, at a much slower rate than CTRB2, suggesting that CTRL may not have a significant role in the pancreatic defense mechanisms against inappropriate trypsinogen activation and pancreatitis.

Efficiency Improvements and Discovery of New Substrates for a SARS-CoV-2 Main Protease FRET Assay

The COVID-19 pandemic, caused by the SARS-CoV-2 virus, has a huge impact on the world. Although several vaccines have recently reached the market, the development of specific antiviral drugs against SARS-CoV-2 is an important additional strategy in fighting the pandemic. One of the most promising pharmacological targets is the viral main protease (M^pro). Here, we present an optimized biochemical assay procedure for SARS-CoV-2 M^pro. We have comprehensively investigated the influence of different buffer components and conditions on the assay performance and characterized Förster resonance energy transfer (FRET) substrates with a preference for 2-Abz/Tyr(3-NO₂) FRET pairs. The substrates 2-AbzSAVLQSGTyr(3-NO₂)R-OH, a truncated version of the established DABCYL/EDANS FRET substrate, and 2-AbzVVTLQSGTyr(3-NO₂)R-OH are promising candidates for screening and inhibitor characterization. In the latter substrate, the incorporation of Val at position P5 improved the catalytic efficiency. Based on the obtained results, we present here a reproducible, reliable assay protocol using highly affordable buffer components.

In Silico Mining of Terpenes from Red-Sea Invertebrates for SARS-CoV-2 Main Protease (Mpro) Inhibitors

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent for the COVID-19 pandemic, which generated more than 1.82 million deaths in 2020 alone, in addition to 83.8 million infections. Currently, there is no antiviral medication to treat COVID-19. In the search for drug leads, marine-derived metabolites are reported here as prospective SARS-CoV-2 inhibitors. Two hundred and twenty-seven terpene natural products isolated from the biodiverse Red-Sea ecosystem were screened for inhibitor activity against the SARS-CoV-2 main protease (Mpro) using molecular docking and molecular dynamics (MD) simulations combined with molecular mechanics/generalized Born surface area binding energy calculations. On the basis of in silico analyses, six terpenes demonstrated high potency as Mpro inhibitors with ΔGbinding ≤ -40.0 kcal/mol. The stability and binding affinity of the most potent metabolite, erylosides B, were compared to the human immunodeficiency virus protease inhibitor, lopinavir. Erylosides B showed greater binding affinity towards SARS-CoV-2 Mpro than lopinavir over 100 ns with ΔGbinding values of -51.9 vs. -33.6 kcal/mol, respectively. Protein-protein interactions indicate that erylosides B biochemical signaling shares gene components that mediate severe acute respiratory syndrome diseases, including the cytokine- and immune-signaling components BCL2L1, IL2, and PRKC. Pathway enrichment analysis and Boolean network modeling were performed towards a deep dissection and mining of the erylosides B target-function interactions. The current study identifies erylosides B as a promising anti-COVID-19 drug lead that warrants further in vitro and in vivo testing.

Glycosaminoglycans from Litopenaeus vannamei Inhibit the Alzheimer's Disease β Secretase, BACE1

Only palliative therapeutic options exist for the treatment of Alzheimer's Disease; no new successful drug candidates have been developed in over 15 years. The widely used clinical anticoagulant heparin has been reported to exert beneficial effects through multiple pathophysiological pathways involved in the aetiology of Alzheimer's Disease, for example, amyloid peptide production and clearance, tau phosphorylation, inflammation and oxidative stress. Despite the therapeutic potential of heparin as a multi-target drug for Alzheimer's disease, the repurposing of pharmaceutical heparin is proscribed owing to the potent anticoagulant activity of this drug. Here, a heterogenous non-anticoagulant glycosaminoglycan extract, obtained from the shrimp Litopenaeus vannamei, was found to inhibit the key neuronal β-secretase, BACE1, displaying a more favorable therapeutic ratio compared to pharmaceutical heparin when anticoagulant activity is considered.

Iripin-3, a New Salivary Protein Isolated From Ixodes ricinus Ticks, Displays Immunomodulatory and Anti-Hemostatic Properties In Vitro

Tick saliva is a rich source of pharmacologically and immunologically active molecules. These salivary components are indispensable for successful blood feeding on vertebrate hosts and are believed to facilitate the transmission of tick-borne pathogens. Here we present the functional and structural characterization of Iripin-3, a protein expressed in the salivary glands of the tick Ixodes ricinus, a European vector of tick-borne encephalitis and Lyme disease. Belonging to the serpin superfamily of protease inhibitors, Iripin-3 strongly inhibited the proteolytic activity of serine proteases kallikrein and matriptase. In an in vitro setup, Iripin-3 was capable of modulating the adaptive immune response as evidenced by reduced survival of mouse splenocytes, impaired proliferation of CD4+ T lymphocytes, suppression of the T helper type 1 immune response, and induction of regulatory T cell differentiation. Apart from altering acquired immunity, Iripin-3 also inhibited the extrinsic blood coagulation pathway and reduced the production of pro-inflammatory cytokine interleukin-6 by lipopolysaccharide-stimulated bone marrow-derived macrophages. In addition to its functional characterization, we present the crystal structure of cleaved Iripin-3 at 1.95 Å resolution. Iripin-3 proved to be a pluripotent salivary serpin with immunomodulatory and anti-hemostatic properties that could facilitate tick feeding via the suppression of host anti-tick defenses. Physiological relevance of Iripin-3 activities observed in vitro needs to be supported by appropriate in vivo experiments.

Insights into the Role of Tick Salivary Protease Inhibitors during Ectoparasite-Host Crosstalk

Protease inhibitors (PIs) are ubiquitous regulatory proteins present in all kingdoms. They play crucial tasks in controlling biological processes directed by proteases which, if not tightly regulated, can damage the host organism. PIs can be classified according to their targeted proteases or their mechanism of action. The functions of many PIs have now been characterized and are showing clinical relevance for the treatment of human diseases such as arthritis, hepatitis, cancer, AIDS, and cardiovascular diseases, amongst others. Other PIs have potential use in agriculture as insecticides, anti-fungal, and antibacterial agents. PIs from tick salivary glands are special due to their pharmacological properties and their high specificity, selectivity, and affinity to their target proteases at the tick-host interface. In this review, we discuss the structure and function of PIs in general and those PI superfamilies abundant in tick salivary glands to illustrate their possible practical applications. In doing so, we describe tick salivary PIs that are showing promise as drug candidates, highlighting the most promising ones tested in vivo and which are now progressing to preclinical and clinical trials.

Inhibition of Protease and Egg Hatching of Haemonchus contortus by Soybean Seed Exudates

Gastrointestinal nematode infection of small ruminants causes losses in livestock production. Plant compounds show promises as alternatives to commercial anthelmintics that have been exerting selective pressures that lead to the development of drug-resistant parasites. Soybean (Glycine max) is an economical value crop, with a higher protein content compared to other legumes. The objective of this study was to evaluate whether the protease inhibitors exuded from the G. max mature seeds have anthelmintic activity against Haemonchus contortus. To obtain the soybean exudates (SEX), mature seeds were immersed in 100 mM sodium acetate buffer, pH 5.0, at 10 C, for 24 hr. Then the naturally released substances present in SEX were collected and exhaustively dialyzed (cutoff 12 kDa) against distilled water. The dialyzed seed exudates (SEXD) were heated at 100 C for 10 min and centrifuged (12,000 g, at 4 C for 15 min). The supernatant obtained was recovered and designated as the heat-treated exudate fraction (SEXDH). The protein content, protease inhibitor activity, and the effect of each fraction on H. contortus egg hatch rate were evaluated. The inhibition extent of SEX, SEXD, and SEXDH on H. contortus egg proteases was 31.1, 42.9, and 63.8%, respectively. Moreover, SEX, SEXD, and SEXDH inhibited the egg hatching with EC50 of 0.175, 0.175, and 0.241 mg ml-1, respectively. Among the commercial protease inhibitors tested, only EDTA and E-64 inhibited the H. contortus hatch rate (79.0 and 28.9%, respectively). We present evidence demonstrating that soybean exudate proteins can effectively inhibit H. contortus egg hatching. This bioactivity is displayed by thermostable proteins and provides evidence that protease inhibitors are a potential candidate for anthelmintic use.

GB-2 inhibits ACE2 and TMPRSS2 expression: In vivo and in vitro studies

After the first case of Coronavirus disease 2019 (COVID-19) was reported in Wuhan, COVID-19 has rapidly spread to almost all parts of world. Angiotensin converting enzyme 2 (ACE2) receptor can bind to spike protein of SARS-CoV-2. Then, the spike protein of SARS-CoV-2 can be cleaved and activated by transmembrane protease, serine 2 (TMPRSS2) of the host cells for SARS-CoV-2 infection. Therefore, ACE2 and TMPRSS2 are potential antiviral targets for treatment of prevention of SARS-CoV-2 infection. In this study, we discovered that 10-250 μg/mL of GB-2, from Tian Shang Sheng Mu of Chiayi Puzi Peitian Temple, can inhibit ACE2 mRNA expression and ACE2 and TMPRSS2 protein expression in HepG2 and 293 T cells without cytotoxicity. GB-2 treatment could decrease ACE2 and TMPRSS2 expression level of lung tissue and kidney tissue without adverse effects, including nephrotoxicity and hepatotoxicity, in animal model. In the compositions of GB-2, we discovered that 50 μg/mL of theaflavin could inhibit protein expression of ACE2 and TMPRSS2. Theaflavin could inhibit the mRNA expression of ACE2. In conclusion, our results suggest that GB-2 and theaflavin could act as potential compounds for ACE2 and TMPRSS2 inhibitors in the further clinical study.

Biochemical and Computational Approach of Selected Phytocompounds from Tinospora crispa in the Management of COVID-19

A pandemic caused by the novel coronavirus (SARS-CoV-2 or COVID-19) began in December 2019 in Wuhan, China, and the number of newly reported cases continues to increase. More than 19.7 million cases have been reported globally and about 728,000 have died as of this writing (10 August 2020). Recently, it has been confirmed that the SARS-CoV-2 main protease (Mpro) enzyme is responsible not only for viral reproduction but also impedes host immune responses. The Mpro provides a highly favorable pharmacological target for the discovery and design of inhibitors. Currently, no specific therapies are available, and investigations into the treatment of COVID-19 are lacking. Therefore, herein, we analyzed the bioactive phytocompounds isolated by gas chromatography-mass spectroscopy (GC-MS) from Tinospora crispa as potential COVID-19 Mpro inhibitors, using molecular docking study. Our analyses unveiled that the top nine hits might serve as potential anti-SARS-CoV-2 lead molecules, with three of them exerting biological activity and warranting further optimization and drug development to combat COVID-19.

Partial Characterization of Protease Inhibitors of Ulva ohnoi and Their Effect on Digestive Proteases of Marine Fish

This piece of research evaluates the presence of protease inhibitors in the macroalga Ulva ohnoi and provides an initial overview of their mode of action. The ability of Ulva protease inhibitors to inhibit digestive proteases of three marine fish species, as well as their capacity to hamper the hydrolysis of a reference protein by those fish proteases, were assessed. In addition, thermal stability and the mode of inhibition on trypsin and chymotrypsin were also studied. Dose-response inhibition curves and in vitro protein hydrolysis assays revealed a noticeable inhibition of fish enzymes when Ulva concentration increased in the assay. The thermal treatment of Ulva reduced markedly the inhibitory effect on fish digestive protease. Finally, Lineweaver-Burk plots indicated that trypsin and chymotrypsin inhibition consisted of a mixed-type inhibition mechanism in which the inhibitory effect depends on Ulva concentration. Overall, the results confirmed the presence of protease inhibitors in Ulva, though heat treatment was enough for inactivating these compounds.

<i>Syzygium samarangense</i> Volatile Oil Inhibited Bacteria Growth and Extracellular Protease of <i>Salmonella typhimurium</i>

BACKGROUND AND OBJECTIVE

Medicinal plants are fast becoming essential pharmaceuticals for disease and infection management. The vast antimicrobial properties of these plants reside in the inhibitory properties of their endogenous secondary metabolites. Therefore, this study aimed to assess if the volatile oil of Syzygium samarangense inhibits enteric bacteria growth and its effect against the caseinolytic activity of the extracellular protease of Salmonella typhimurium.

MATERIALS AND METHODS

The volatile oil was extracted by hydrodistillation, while the antimicrobial assay was assessed with the microdilution method. The extracellular protease was partially purified by salting out, followed by size-exclusion chromatography. The mode of inhibition of this enzyme was deduced from the enzyme-substrate kinetics using a line-weaver burke plot.

RESULTS

The antimicrobial properties of the oil were reported against ten enteric bacteria. Proteus vulgaris has the highest IC50 value of 0.75±0.004% v/v, while S. typhimurium, the most sensitive bacterium, showed the lowest IC50 value of 0.17±0.005% v/v. The extracellular protease of S. typhimurium was partially purified to achieve 3.73 purification fold and 314.2 μmol min-1 mg-1 protein. The optimal caseinolytic activity of this enzyme was found at pH 7.5 and 40 °C. The protease showed significantly higher activity in the presence of Zn2+ (9.3±0.33 U min-1) as compared to the control (7.0±0.58 U min-1) (p<0.05), however, K+, Ca2+, Co2+, Ba2+, Pb2+ and Hg2+ considerably reduced the enzyme activity. The activity of this enzyme was competitively inhibited by the volatile oil as an inhibitor.

CONCLUSION

The volatile oil of S. samarangense inhibited a wide range of enteric bacteria and, therefore proposed as a potential antimicrobial agent. Inhibiting the extracellular protease of S. typhimurium may be one of its modes of action against these pathogens.

Natural Bioactive Compounds from Fungi as Potential Candidates for Protease Inhibitors and Immunomodulators to Apply for Coronaviruses

The inhibition of viral protease is an important target in antiviral drug discovery and development. To date, protease inhibitor drugs, especially HIV-1 protease inhibitors, have been available for human clinical use in the treatment of coronaviruses. However, these drugs can have adverse side effects and they can become ineffective due to eventual drug resistance. Thus, the search for natural bioactive compounds that were obtained from bio-resources that exert inhibitory capabilities against HIV-1 protease activity is of great interest. Fungi are a source of natural bioactive compounds that offer therapeutic potential in the prevention of viral diseases and for the improvement of human immunomodulation. Here, we made a brief review of the current findings on fungi as producers of protease inhibitors and studies on the relevant candidate fungal bioactive compounds that can offer immunomodulatory activities as potential therapeutic agents of coronaviruses in the future.

Exploration of Carica papaya bioactive compounds as potential inhibitors of dengue NS2B, NS3 and NS5 protease

Current outbreak of dengue has shown serious health concerns in Pakistan. The present study reports the anti-dengue potential of Carica papaya natural compounds. The leaves of C. papaya have previously shown promising results in cure of Dengue fever. The aim of this project is to find specific bioactive compounds by computational screening and biological activities of C. papaya against serine NS2B, NS3 and NS5 proteases of dengue virus. Docking study resulted in the screening of nine bioactive compounds having highest docking scores. However, three compounds namely epigallocatchin, catechin and protocatechuric acid had the strongest binding affinity with the active residues i.e., Ser135, His51 and Asp75 of dengue virus serine proteases. Results also indicated that the extract of C. papaya was a strong antimicrobial and antioxidant agent. It is concluded that the C. papaya compounds can be commercially applied for medical formulations against dengue virus.

Proteomic Comparison of Three Extraction Methods Reveals the Abundance of Protease Inhibitors in the Seeds of Grass Pea, a Unique Orphan Legume

Grass pea is an orphan legume that is grown in many places in the world. It is a high-protein, drought-tolerant legume that is capable of surviving extreme environmental challenges and can be a sole food source during famine. However, grass pea produces the neurotoxin β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP), which can cause a neurological disease. This crop is promising as a food source for both animals and humans if β-ODAP levels and other antinutritional factors such as protease inhibitors are lowered or removed. To understand more about these proteins, a proteomic analysis of grass pea was conducted using three different extraction methods to determine which was more efficient at isolating antinutritional factors. Seed proteins extracted with Tris-buffered saline (TBS), 30% ethanol, and 50% isopropanol were identified by mass spectrometry, resulting in the documentation of the most abundant proteins for each extraction method. Mass spectrometry spectral data and BLAST2GO analysis led to the identification of 1376 proteins from all extraction methods. The molecular function of the extracted proteins revealed distinctly different protein functional profiles. The majority of the TBS-extracted proteins were annotated with nutrient reservoir activity, while the isopropanol extraction yielded the highest percentage of endopeptidase proteinase inhibitors. Our results demonstrate that the 50% isopropanol extraction method was the most efficient at isolating antinutritional factors including protease inhibitors.

The effect of entomopathogenic fungal culture filtrate on the immune response and haemolymph proteome of the large pine weevil, Hylobius abietis

The large pine weevil Hylobius abietis L. is a major forestry pest in 15 European countries, where it is a threat to 3.4 million hectares of forest. A cellular and proteomic analysis of the effect of culture filtrate of three entomopathogenic fungi (EPF) species on the immune system of H. abietis was performed. Injection with Metarhizium brunneum or Beauvaria bassiana culture filtrate facilitated a significantly increased yeast cell proliferation in larvae. Larvae co-injected with either Beauvaria caledonica or B. bassiana culture filtrate and Candida albicans showed significantly increased mortality. Together these results suggest that EPF culture filtrate has the potential to modulate the insect immune system allowing a subsequent pathogen to proliferate. Injection with EPF culture filtrate was shown to alter the abundance of protease inhibitors, detoxifing enzymes, antimicrobial peptides and proteins involved in reception/detection and development in H. abietis larvae. Larvae injected with B. caledonica culture filtrate displayed significant alterations in abundance of proteins involved in cellulolytic and other metabolic processes in their haemolymph proteome. Screening EPF for their ability to modulate the insect immune response represents a means of assessing EPF for use as biocontrol agents, particularly if the goal is to use them in combination with other control agents.

A Bowman-Birk Inhibitor from the Seeds of Luetzelburgia auriculata Inhibits Staphylococcus aureus Growth by Promoting Severe Cell Membrane Damage

Staphylococcus aureus is a multidrug-resistant bacterium responsible for several cases of hospital-acquired infections, which constitute a global public health problem. The introduction of new healthcare strategies and/or the discovery of molecules capable of inhibiting the growth or killing S. aureus would have a huge impact on the treatment of S. aureus-mediated diseases. Herein, a Bowman-Birk protease inhibitor ( LzaBBI), with strong in vitro antibacterial activity against S. aureus, was purified to homogeneity from Luetzelburgia auriculata seeds. LzaBBI in its native form is a 14.3 kDa protein and has a pI of 4.54, and its NH₂-terminal sequence has high identity with other Bowman-Birk inhibitors. LzaBBI showed a mixed-type inhibitory activity against both trypsin and chymotrypsin, respectively, and it remained stable after both boiling at 98 °C for 120 min and incubation at various pHs. Scanning electron microscopy revealed that LzaBBI disrupted the S. aureus membrane integrity, leading to bacterial death. This study suggests that LzaBBI is a powerful candidate for developing a new antimicrobial to overcome drug resistance toward reducing hospital-acquired infections caused by S. aureus.

Identification of a 3-Alkylpyridinium Compound from the Red Sea Sponge Amphimedon chloros with In Vitro Inhibitory Activity against the West Nile Virus NS3 Protease

Viruses are underrepresented as targets in pharmacological screening efforts, given the difficulties of devising suitable cell-based and biochemical assays. In this study we found that a pre-fractionated organic extract of the Red Sea sponge Amphimedon chloros was able to inhibit the West Nile Virus NS3 protease (WNV NS3). Using liquid chromatography⁻mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) spectroscopy, the identity of the bioactive compound was determined as a 3-alkylpyridinium with m/z = 190.16. Diffusion Ordered Spectroscopy (DOSY) NMR and NMR relaxation rate analysis suggest that the bioactive compound forms oligomers of up to 35 kDa. We observed that at 9.4 μg/mL there was up to 40⁻70% inhibitory activity on WNV NS3 protease in orthogonal biochemical assays for solid phase extracts (SPE) of A. chloros. However, the LC-MS purified fragment was effective at inhibiting the protease up to 95% at an approximate amount of 2 µg/mL with negligible cytotoxicity to HeLa cells based on a High-Content Screening (HCS) cytological profiling strategy. To date, 3-alkylpyridinium type natural products have not been reported to show antiviral activity since the first characterization of halitoxin, or 3-alkylpyridinium, in 1978. This study provides the first account of a 3-alkylpyridinium complex that exhibits a proposed antiviral activity by inhibiting the NS3 protease. We suggest that the here-described compound can be further modified to increase its stability and tested in a cell-based assay to explore its full potential as a potential novel antiviral capable of inhibiting WNV replication.

Biochemical and MALDI-TOF Mass Spectrometric Characterization of a Novel Native and Recombinant Cystine Knot Miniprotein from Solanum tuberosum subsp. andigenum cv. Churqueña

Cystine-knot miniproteins (CKMPs) are an intriguing group of cysteine-rich molecules that combine the characteristics of proteins and peptides. Typically, CKMPs are fewer than 50 residues in length and share a characteristic knotted scaffold characterized by the presence of three intramolecular disulfide bonds that form the singular knotted structure. The knot scaffold confers on these proteins remarkable chemical, thermal, and proteolytic stability. Recently, CKMPs have emerged as a novel class of natural molecules with interesting pharmacological properties. In the present work, a novel cystine-knot metallocarboxypeptidase inhibitor (chuPCI) was isolated from tubers of Solanum tuberosum, subsp. andigenum cv. Churqueña. Our results demonstrated that chuPCI is a member of the A/B-type family of metallocarboxypeptidases inhibitors. chuPCI was expressed and characterized by a combination of biochemical and mass spectrometric techniques. Direct comparison of the MALDI-TOF mass spectra for the native and recombinant molecules allowed us to confirm the presence of four different forms of chuPCI in the tubers. The majority of such forms have a molecular weight of 4309 Da and contain a cyclized Gln in the N-terminus. The other three forms are derived from N-terminal and/or C-terminal proteolytic cleavages. Taken together, our results contribute to increase the current repertoire of natural CKMPs.

Novel Peptidase Kunitz Inhibitor from Platypodium elegans Seeds Is Active against Spodoptera frugiperda Larvae

A novel Kunitz-type inhibitor from Platypodium elegans seeds (PeTI) was purified and characterized. The mass spectrometry analyses of PeTI indicated an intact mass of 19 701 Da and a partial sequence homologous to Kunitz inhibitors. PeTI was purified by ion exchange and affinity chromatographies. A complex with a 1:1 ratio was obtained only for bovine trypsin, showing a K_i = 0.16 nM. Stability studies showed that PeTI was stable over a wide range of temperature (37-80 °C) and pH (2-10). The inhibitory activity of PeTI was affected by dithiothreitol (DTT). Bioassays of PeTI on Spodoptera frugiperda showed negative effects on larval development and weight gain, besides extending the insect life cycle. The activities of digestive enzymes, trypsin and chymotrypsin, were reduced by feeding larvae with 0.2% PeTI in an artificial diet. In summary, we describe a novel Kunitz inhibitor with promising biotechnological potential for pest control.

Identification, In Vitro Testing and Molecular Docking Studies of Microginins' Mechanism of Angiotensin-Converting Enzyme Inhibition

Cyanobacteria are able to produce a wide range of secondary metabolites, including toxins and protease inhibitors, with diverse biological activities. Microginins are small linear peptides biosynthesized by cyanobacteria species that act against proteases. The aim of this study was to isolate and identify microginins produced by the LTPNA08 strain of Microcystis aeruginosa, as well as to verify their potential to inhibit angiotensin-converting enzyme (ACE; EC. 3.4.15.1) using in vitro and in silico methods. The fractionation of cyanobacterial extracts was performed by liquid chromatography and the presence of microginins was monitored by both LC-MS and an ACE inhibition assay. Enzyme inhibition was assayed by ACE with hippuryl-histidyl-leucine as the substrate; monitoring of hippuric acid was performed by HPLC-DAD. Isolated microginins were confirmed by mass spectrometry and were used to carry out the enzymatic assay. Molecular docking was used to evaluate microginin 770 (MG 770) and captopril (positive control), in order to predict similar binding interactions and determine the inhibitory action of ACE. The enzyme assay confirmed that MG 770 can efficiently inhibit ACE, with an IC₅₀ equivalent to other microginins. MG 770 presented with comparable interactions with ACE, having features in common with commercial inhibitors such as captopril and enalaprilate, which are frequently used in the treatment of hypertension in humans.

Characterization and Identification of Cryptic Biopeptides in Carya illinoinensis (Wangenh K. Koch) Storage Proteins

The objective of this research was to identify and characterize the encoded peptides present in nut storage proteins of Carya illinoinensis. It was found, through in silico prediction, proteomic analysis, and MS spectrometry, that bioactive peptides were mainly found in albumin and glutelin fractions. Glutelin was the major fraction with ~53% of the nut storage proteins containing at least 21 peptides with different putative biological activities, including antihypertensives, antioxidants, immunomodulators, protease inhibitors, and inhibitors of cell cycle progression in cancer cells. Data showed that using 50 μg/mL tryptic digests of enriched peptides obtained from nut glutelins is able to induce up to 19% of apoptosis in both HeLa and CasKi cervical cancer cells. To our knowledge, this is the first report that shows the potential value of the nut-encoded peptides to be considered as adjuvants in cancer therapies.

Cyclotheonellazoles A-C, Potent Protease Inhibitors from the Marine Sponge Theonella aff. swinhoei

The extract of a sample of the sponge Theonella aff. swinhoei collected in Madagascar exhibited promising in vitro antiplasmodial activity. The antiplasmodial activity was ascribed in part to the known metabolite swinholide A. Further investigation of the extract afforded three unusual cyclic peptides, cyclotheonellazoles A-C (1-3), which contain six nonproteinogenic amino acids out of the eight acid units that compose these natural products. Among these acids the most novel were 4-propenoyl-2-tyrosylthiazole and 3-amino-4-methyl-2-oxohexanoic acid. The structure of the compounds was elucidated by interpretation of the 1D and 2D NMR data, HRESIMS, and advanced Merfay's techniques. The new compounds were found to be nanomolar inhibitors of chymotrypsin and sub-nanomolar inhibitors of elastase, but did not present antiplasmodial activity.

Peanut Seed Cultivars with Contrasting Resistance to Aspergillus parasiticus Colonization Display Differential Temporal Response of Protease Inhibitors

Significant efforts are being made to minimize aflatoxin contamination in peanut seeds and one possible strategy is to understand and exploit the mechanisms of plant defense against fungal infection. In this study we have identified and characterized, at biochemical and molecular levels, plant protease inhibitors (PPIs) produced in peanut seeds of the resistant PI 337394 and the susceptible Forman cultivar during Aspergillus parasiticus colonization. With chromatographic methods and 2D-electrophoresis-mass spectrometry we have isolated and identified four variants of Bowman-Birk trypsin inhibitor (BBTI) and a novel Kunitz-type protease inhibitor (KPI) produced in response to A. parasiticus colonization. KPI was detected only in the resistant cultivar, while BBTI was produced in the resistant cultivar in a higher concentration than susceptible cultivar and with different isoforms. The kinetic expression of KPI and BBTI genes along with trypsin inhibitory activity was analyzed in both cultivars during infection. In the susceptible cultivar an early PPI activity response was associated with BBTI occurrence. Meanwhile, in the resistant cultivar a later response with a larger increase in PPI activity was associated with BBTI and KPI occurrence. The biological significance of PPI in seed defense against fungal infection was analyzed and linked to inhibitory properties on enzymes released by the fungus during infection, and to the antifungal effect of KPI.

High-throughput screening for the identification of small-molecule inhibitors of the flaviviral protease

The mosquito-borne dengue virus serotypes 1-4 (DENV1-4) and West Nile virus (WNV) cause serious illnesses worldwide associated with considerable morbidity and mortality. According to the World Health Organization (WHO) estimates, there are about 390 million infections every year leading to ∼500,000 dengue haemorrhagic fever (DHF) cases and ∼25,000 deaths, mostly among children. Antiviral therapies could reduce the morbidity and mortality associated with flaviviral infections, but currently there are no drugs available for treatment. In this study, a high-throughput screening assay for the Dengue protease was employed to screen ∼120,000 small molecule compounds for identification of inhibitors. Eight of these inhibitors have been extensively analyzed for inhibition of the viral protease in vitro and cell-based viral replication using Renilla luciferase reporter replicon, infectivity (plaque) and cytotoxicity assays. Three of these compounds were identified as potent inhibitors of DENV and WNV proteases, and viral replication of DENV2 replicon and infectious RNA. Fluorescence quenching, kinetic analysis and molecular modeling of these inhibitors into the structure of NS2B-NS3 protease suggest a mode of inhibition for three compounds that they bind to the substrate binding pocket.

The Daiokanzoto (TJ-84) Kampo Formulation Reduces Virulence Factor Gene Expression in Porphyromonas gingivalis and Possesses Anti-Inflammatory and Anti-Protease Activities

Kampo formulations used in Japan to treat a wide variety of diseases and to promote health are composed of mixtures of crude extracts from the roots, bark, leaves, and rhizomes of a number of herbs. The present study was aimed at identifying the beneficial biological properties of Daiokanzoto (TJ-84), a Kampo formulation composed of crude extracts of Rhubarb rhizomes and Glycyrrhiza roots, with a view to using it as a potential treatment for periodontal disease. Daiokanzoto dose-dependently inhibited the expression of major Porphyromonas gingivalis virulence factors involved in host colonization and tissue destruction. More specifically, Daiokanzoto reduced the expression of the fimA, hagA, rgpA, and rgpB genes, as determined by quantitative real-time PCR. The U937-3xκB-LUC monocyte cell line transfected with a luciferase reporter gene was used to evaluate the anti-inflammatory properties of Daiokanzoto. Daiokanzoto attenuated the P. gingivalis-mediated activation of the NF-κB signaling pathway. It also reduced the secretion of pro-inflammatory cytokines (IL-6 and CXCL8) by lipopolysaccharide-stimulated oral epithelial cells and gingival fibroblasts. Lastly, Daiokanzoto, dose-dependently inhibited the catalytic activity of matrix metalloproteinases (-1 and -9). In conclusion, the present study provided evidence that Daiokanzoto shows potential for treating and/or preventing periodontal disease. The ability of this Kampo formulation to act on both bacterial pathogens and the host inflammatory response, the two etiological components of periodontal disease, is of high therapeutic interest.

In Vitro Mode of Action and Anti-thrombotic Activity of Boophilin, a Multifunctional Kunitz Protease Inhibitor from the Midgut of a Tick Vector of Babesiosis, Rhipicephalus microplus

Background

Hematophagous mosquitos and ticks avoid host hemostatic system through expression of enzyme inhibitors targeting proteolytic reactions of the coagulation and complement cascades. While most inhibitors characterized to date were found in the salivary glands, relatively few others have been identified in the midgut. Among those, Boophilin is a 2-Kunitz multifunctional inhibitor targeting thrombin, elastase, and kallikrein. However, the kinetics of Boophilin interaction with these enzymes, how it modulates platelet function, and whether it inhibits thrombosis in vivo have not been determined.

Methodology/Principal Findings

Boophilin was expressed in HEK293 cells and purified to homogeneity. Using amidolytic assays and surface plasmon resonance experiments, we have demonstrated that Boophilin behaves as a classical, non-competitive inhibitor of thrombin with respect to small chromogenic substrates by a mechanism dependent on both exosite-1 and catalytic site. Inhibition is accompanied by blockade of platelet aggregation, fibrin formation, and clot-bound thrombin in vitro. Notably, we also identified Boophilin as a non-competitive inhibitor of FXIa, preventing FIX activation. In addition, Boophilin inhibits kallikrein activity and the reciprocal activation, indicating that it targets the contact pathway. Furthermore, Boophilin abrogates cathepsin G- and plasmin-induced platelet aggregation and partially affects elastase-mediated cleavage of Tissue Factor Pathway Inhibitor (TFPI). Finally, Boophilin inhibits carotid artery occlusion in vivo triggered by FeCl₃, and promotes bleeding according to the mice tail transection method.

Conclusion/Significance

Through inhibition of several enzymes involved in proteolytic cascades and cell activation, Boophilin plays a major role in keeping the midgut microenvironment at low hemostatic and inflammatory tonus. This response allows ticks to successfully digest a blood meal which is critical for metabolism and egg development. Boophilin is the first tick midgut FXIa anticoagulant also found to inhibit thrombosis.

Hematophagous animals express a repertoire of anti-hemostatics which target enzymes involved in proteolytic reactions. These molecules are present in the salivary glands or midguts and target components of both coagulation and complement cascades, in addition to cells involved in hemostasis and immune system. These inhibitors are critical for development and survival of mosquitoes and ticks, and might also contribute to parasite transmission and completion of their life cycle. While much is known regarding sialomics and functional genomics of the salivary glands components, comparatively less information has been gained over the years with respect to midgut anti-hemostatics and their mechanisms of action. The vector of Babesiosis and Q fever, Rhipicephalus microplus, expresses Boophilin, a midgut thrombin inhibitor with low specificity, which contributes to tick development. Notably, we reported that Boophilin targets FXIa, kallikrein, and neutrophil enzymes elastase and cathepsin G, which play a direct or indirect role in the contact pathway of the coagulation cascade. Boophilin also abrogates platelet aggregation by cathepsin G and plasmin, and attenuates Tissue Factor Pathway Inhibitor cleavage by elastase. In vivo, Boophilin inhibits thrombosis and promotes bleeding in mice. It is concluded that Boophilin redundantly down-modulates host biochemical reactions involved in mounting and sustaining pro-inflammatory events which are detrimental to tick development.

A Helminth Protease Inhibitor Modulates the Lipopolysaccharide-Induced Proinflammatory Phenotype of Microglia in vitro

OBJECTIVE

The aim of this study was to examine whether the natural protease inhibitor Av-cystatin (rAv17) of the parasitic nematode Acanthocheilonema viteae exerts anti-inflammatory effects in an in vitro model of lipopolysaccharide (LPS)-activated microglia.

METHODS

Primary microglia were harvested from the brains of 2-day-old Wistar rats and cultured with or without rAv17 (250 nM). After 6 and 24 h the release of nitric oxide (Griess reagent) and TNF-α (ELISA) was measured in the supernatant. Real-time PCR was performed after 2, 6 and 24 h of culture to measure the mRNA expression of IL-1β, IL-6, TNF-α, COX-2, iNOS and IL-10. To address the involved signaling pathways, nuclear NF-x0138;B translocation was visualized by immunocytochemistry. Morphological changes of microglia were analyzed by Coomassie blue staining. Differences between groups were calculated using one-way ANOVA with Bonferroni's post hoc test.

RESULTS

Morphological analysis indicated that LPS-induced microglial transformation towards an amoeboid morphology is inhibited by rAv17. Av-cystatin caused a time-dependent downregulation of proinflammatory cytokines, iNOS and COX-2 mRNA expression, respectively. This was paralleled by an upregulated expression of IL-10 in resting as well as in LPS-stimulated microglia. Av-cystatin reduced the release of NO and TNF-α in the culture supernatant. Immunocytochemical staining demonstrated an attenuated translocation of NF-x0138;B by Av-cystatin in response to LPS. In addition, Western blot analysis revealed a rAv17-dependent reduction of the LPS-induced ERK1/2-pathway activation.

CONCLUSION

The parasite-derived secretion product Av-cystatin inhibits proinflammatory mechanisms of LPS-induced microglia with IL-10, a potential key mediator.

Bromotyrosine-derived metabolites from an Indonesian marine sponge in the family Aplysinellidae (Order Verongiida)

Seven new bromotyrosine-derived metabolites, purpuramine M-N (1-2), araplysillin VII-XI (3-7) and six known compounds (8-13) were isolated from an Indonesian sponge belonging to the family Aplysinellidae (Order Verongiida). The structures of the new compounds were determined by extensive NMR experiments and mass spectrometric measurements. These compounds were screened against BACE1 and five cancer cell lines.

Bowman-Birk proteinase inhibitor from Clitoria fairchildiana seeds: Isolation, biochemical properties and insecticidal potential

Herein described is the biochemical characterisation, including in vitro and in vivo assays, for a proteinase inhibitor purified from Clitoria fairchildiana seeds (CFPI). Purification was performed by hydrophobic interaction and gel filtration chromatography. Kinetic studies of the purified inhibitor showed a competitive-type inhibitory activity against bovine trypsin and chymotrypsin, with an inhibition stoichiometry of 1:1 for both enzymes. The inhibition constants against trypsin and chymotrypsin were 3.3 × 10(-10) and 1.5 × 10(-10)M, respectively, displaying a tight binding property. SDS-PAGE showed that CFPI has a single polypeptide chain with an apparent molecular mass of 15 kDa under non-reducing conditions. However, MALDI-TOF analysis demonstrated a molecular mass of 7.973 kDa, suggesting that CFPI is dimeric in solution. The N-terminal sequence of CFPI showed homology with members of the Bowman-Birk inhibitor family. CFPI remained stable to progressive heating for 30 min to each temperature range of 37 up to 100 °C and CD analysis exhibited no changes in spectra at 207 nm after heating at 90 °C and subsequent cooling. Moreover, CFPI was active over a wide pH range (2-10). In contrast, reduction with DTT resulted in a loss of inhibitory activity against trypsin and chymotrypsin. CFPI also exhibited significant inhibitory activity against larval midgut trypsin enzymes from Anagasta kuehniella (76%), Diatraea saccharalis (59%) and Heliothis virescens (49%). Its insecticidal properties were further analysed by bioassays and confirmed by negative impact on A. kuehniella development.

Radical scavenging, prolyl endopeptidase inhibitory, and antimicrobial potential of a cultured Himalayan lichen Cetrelia olivetorum

CONTEXT

Lichens are source of natural bioactive compounds which are traditionally used to cure a variety of ailments.

OBJECTIVE

The objective of this study is to assess free radical scavenging, prolyl endopeptidase inhibitory (PEPI), and antimicrobial potential of a high altitude lichen species Cetrelia olivetorum (Nyl.) W. L. Culb. & C. F. Culb (Parmeliaceae).

MATERIALS AND METHODS

Lichen C. olivetorum has been cultured in vitro, and optimized culture conditions were implemented in bioreactor to obtain high quantity of biomass for the study of radical scavenging, PEPI, and antimicrobial activities. Radical scavenging activity of methanol extract of Cetrelia olivetorum (MECO) was tested at 100 µg/mL, PEPI activity at 25 and 50 µg/mL, and antimicrobial activity at 5, 25, 50, and 100 µg/mL conc. All the biological activities of natural thallus extract and its derived culture extract were evaluated spectrophotometrically.

RESULTS

Murashige and Skoog medium supplemented with 3% glucose and 100 ppb indole-3-butyric acid (IBA) supported biomass growth at flask level and yielded 5.095 g biomass in bioreactor. MECO of both the cultured and the natural lichen exhibited half inhibiting concentration (IC50) for radical scavenging activities in the range of 50-60 µg/mL, whereas the IC50 value of standard antioxidants was found to be in the range of 12-29 µg/mL. The IC50 value of lichen extract for PEPI activity was 144-288 µg/mL, whereas the IC50 value of standard prolyl endopeptidase inhibitor, Z-pro-prolinal, was 57.73 µg/mL. As far as the antimicrobial activity of MECO is concerned, minimum inhibitory concentration (MIC) value of lichen extracts against tested microorganisms was obtained in the range of 50-104 µg/mL and found to be more effective than commercially available standard erythromycin.

DISCUSSION

Murashige and Skoog medium containing IBA was found to be suitable for maximum biomass production of C. olivetorum under bioreactor conditions. The cultured lichen biomass extract also showed antioxidant, PEPI, and antimicrobial potential.

CONCLUSION

The present study indicates therapeutic potential of Himalayan lichen C. olivetorum against neurodegenerative diseases owing to its radical scavenging, PEPI, and antimicrobial activities. Further, the result encourages its commercial exploitation through mass culture for production of its bioactive components and their use in pharmaceutical and nutraceutical industries.

Mass spectrometry guided venom profiling and bioactivity screening of the Anatolian Meadow Viper, Vipera anatolica

This contribution reports on the first characterization of the venom proteome and the bioactivity screening of Vipera anatolica, the Anatolian Meadow Viper. The crude venom as well as an isolated dimeric disintegrin showed remarkable cytotoxic activity against glioblastoma cells. Due to the rare occurrence and the small size of this species only little amount of venom was available, which was profiled by means of a combination of bottom-up and top-down mass spectrometry. From this analysis we identified snake venom metalloproteases, cysteine-rich secretory protein isoforms, a metalloprotease inhibitor, several type A2 phospholipases, disintegrins, a snake venom serine protease, a C-type lectin and a Kunitz-type protease inhibitor. Furthermore, we detected several isoforms of above mentioned proteins as well as previously unknown proteins, indicating an extensive complexity of the venom which would have remained undetected with conventional venomic approaches.

An effective and simple procedure to isolate abundant quantities of biologically active chemopreventive Lunasin Protease Inhibitor Concentrate (LPIC) from soybean

Lunasin is a 5-kDa soybean bioactive peptide with demonstrated anti-cancer and anti-inflammatory properties. Recently, purification methods have been developed to obtain gram quantities of lunasin. However, these methods are cumbersome, time consuming and cost-prohibitive. To overcome these constrains we have developed a novel method which involves extraction of soybean flour with 30% ethanol followed by preferential precipitation of lunasin and protease inhibitors by calcium. The calcium precipitated protein fraction, which we termed as Lunasin Protease Inhibitor Concentrate (LPIC), contains three abundant proteins with molecular weights of 21, 14 and 5 kDa. This simple procedure yields 3.2g of LPIC from 100g of soybean flour and the entire isolation procedure can be completed in less than 2h. Treatment of THP-1 human monocyte cell lines with LPIC resulted in suppression of lipopolysaccharide-stimulated cytokine expression, demonstrating that the LPIC isolated by our simple procedure is biologically active.

Broad-spectrum inhibitors against 3C-like proteases of feline coronaviruses and feline caliciviruses

Feline infectious peritonitis and virulent, systemic calicivirus infection are caused by certain types of feline coronaviruses (FCoVs) and feline caliciviruses (FCVs), respectively, and are important infectious diseases with high fatality rates in members of the Felidae family. While FCoV and FCV belong to two distinct virus families, the Coronaviridae and the Caliciviridae, respectively, they share a dependence on viral 3C-like protease (3CLpro) for their replication. Since 3CLpro is functionally and structurally conserved among these viruses and essential for viral replication, 3CLpro is considered a potential target for the design of antiviral drugs with broad-spectrum activities against these distinct and highly important viral infections. However, small-molecule inhibitors against the 3CLpro enzymes of FCoV and FCV have not been previously identified. In this study, derivatives of peptidyl compounds targeting 3CLpro were synthesized and evaluated for their activities against FCoV and FCV. The structures of compounds that showed potent dual antiviral activities with a wide margin of safety were identified and are discussed. Furthermore, the in vivo efficacy of 3CLpro inhibitors was evaluated using a mouse model of coronavirus infection. Intraperitoneal administration of two 3CLpro inhibitors in mice infected with murine hepatitis virus A59, a hepatotropic coronavirus, resulted in significant reductions in virus titers and pathological lesions in the liver compared to the findings for the controls. These results suggest that the series of 3CLpro inhibitors described here may have the potential to be further developed as therapeutic agents against these important viruses in domestic and wild cats. This study provides important insights into the structure and function relationships of 3CLpro for the design of antiviral drugs with broader antiviral activities.

IMPORTANCE

Feline infectious peritonitis virus (FIPV) is the leading cause of death in young cats, and virulent, systemic feline calicivirus (vs-FCV) causes a highly fatal disease in cats for which no preventive or therapeutic measure is available. The genomes of these distinct viruses, which belong to different virus families, encode a structurally and functionally conserved 3C-like protease (3CLpro) which is a potential target for broad-spectrum antiviral drug development. However, no studies have previously reported a structural platform for the design of antiviral drugs with activities against these viruses or on the efficacy of 3CLpro inhibitors against coronavirus infection in experimental animals. In this study, we explored the structure-activity relationships of the derivatives of 3CLpro inhibitors and identified inhibitors with potent dual activities against these viruses. In addition, the efficacy of the 3CLpro inhibitors was demonstrated in mice infected with a murine coronavirus. Overall, our study provides the first insight into a structural platform for anti-FIPV and anti-FCV drug development.

The epidermal barrier to Schistosoma mansoni infection

The stratified epithelium serves as protection for underlying tissues and organs, and the structural fitness of the epidermal cells has been extensively reported. We studied the possible roles played by the epidermis as a barrier against the migration of Schistosoma mansoni larvae. Freshly shed cercariae were collected and placed on the back skin of 2-day-old rats. Electron microscopy of biopsies taken at various intervals showed the larvae and their secretory granules in keratinocytes in which the cytoplasm had become homogeneous in appearance. SDS gel electrophoresis showed the digestion of purified epidermal keratin (60K protein) by a proteinase secreted from cercariae, but this activity was inhibited by an inhibitor purified from epidermal cells. These findings suggest that epidermal cells function both structurally and chemically as a barrier against cercariae invasion.

Novel in vitro inhibitory functions of potato tuber proteinaceous inhibitors

Plant protease inhibitors are a structurally highly diverse and ubiquitous class of small proteins, which play various roles in plant development and defense against pests and pathogens. Particular isoforms inhibit in vitro proteases and other enzymes that are not their natural substrates, for example proteases that have roles in human diseases. Mature potato tubers are a rich source of several protease inhibitor families. Different cultivars have different inhibitor profiles. With the objective to explore the functional diversity of the natural diversity of potato protease inhibitors, we randomly selected and sequenced 9,600 cDNA clones originated from mature tubers of ten potato cultivars. Among these, 120 unique inhibitor cDNA clones were identified by homology searches. Eighty-eight inhibitors represented novel sequence variants of known plant protease inhibitor families. Most frequent were Kunitz-type inhibitors (KTI), potato protease inhibitors I and II (PIN), pectin methylesterase inhibitors, metallocarboxypeptidase inhibitors and defensins. Twenty-three inhibitors were functionally characterized after heterologous expression in the yeast Pichia pastoris. The purified recombinant proteins were tested for inhibitory activity on trypsin, eleven pharmacological relevant proteases and the non-proteolytic enzyme 5-lipoxygenase. Members of the KTI and PIN families inhibited pig pancreas elastase, β-Secretase, Cathepsin K, HIV-1 protease and potato 5-lipoxygenase. Our results demonstrate in vitro inhibitory diversity of small potato tuber proteins commonly known as protease inhibitors, which might have biotechnological or medical applications.

[Fish ovarian fluid contains protease inhibitors]

Studies of the conditions under which fish egg is activated spontaneously without the sperm showed that the egg retains the ability for fertilization in the ovarian (coelomic) fluid, which surrounds it in the gonad cavity after ovulation. Earlier, we showed that, in artificial media, the spontaneous activation is suppressed by protease inhibitors. In this study, we investigated the presence of natural protease inhibitors in the ovarian fluid and showed that the ovarian fluid of zebrafish and loach contains protease inhibitors, in particular, type I serpin a, a protein inhibitor of trypsin proteases.

Purification, characterization and molecular cloning of alpha-2-macroglobulin in cobia, Rachycentron canadum

Alpha-2-macroglobulin (α-2-M) is a broad spectrum protease inhibitor which is abundant in the plasma of vertebrates and several invertebrates. The α-2-M was purified from cobia (Rachycentron canadum) plasma by a four-step procedure: poly ethylene glycol fractionation, affinity chromatography, hydrophobic interaction chromatography and ion exchange chromatography on Fast Protein liquid chromatography system in the present study. It migrated as one protein band with a molecular mass of about 360 kDa in the native state, whereas in SDS-PAGE it was about 180 kDa under non-reducing condition. This result revealed that the native protein was a dimer. In addition, it was cleaved into two different fragments of molecular mass about 93 and 87 kDa when reduced by dithiothreitol (DTT). The anti-protease activity of the purified α-2-M was apparently decreased as temperature elevated above 50 °C. The α-2-M exhibited highest protease inhibitory activity at pH 9. The results indicate that the α-2-M is a heat-labile and alkaline protease inhibitor. The purified α-2-M exhibited more than 50% protease inhibitory activity against extracellular products (ECP) of Vibrio alginolytius isolated from diseased cobia. It seems that the protease activities in ECP may be affected by the plasma α-2-M. The protease inhibitory activities of cobia plasma or purified α-2-M were decreased when incubated with 10 mM methylamine for 30 min. The α-2-M cDNA consisted of 4611 bp with an open reading frame of 4374 bp had been cloned from cobia liver. This sequence contained thioester domain (GCGEQ) and thirteen predicted N-linked glycosylation sites. In addition, the amino acid sequence of thioester domain and genes of adjacent regions of cobia α-2-M were further compared with sequences of known fish species in GenBank. The unweighted pair group method using arithmetic average (UPGMA) was employed to construct the phylogenetic trees of α-2-M among different fish species (freshwater fish, sea water fish and primitive fish), and all these fish species were then clustered into three groups. The cobia α-2-M was closer to that of sea water fish than that of freshwater fish compared basing on its similarity of amino acid sequence and phylogenetic analysis of the partial gene.

Isolation and characterization of a protease inhibitor from Acacia karroo with a common combining loop and overlapping binding sites for chymotrypsin and trypsin

By using affinity and reversed-phase HPLC (RP-HPLC) chromatographies two chymotrypsin-trypsin inhibitors were isolated from seeds of Acacia karroo, a legume of the subfamily Mimosoideae. The primary structure of one of these inhibitors, named AkCI/1, was determined. The inhibitor consists of two polypeptide chains, 139 and 44 residues respectively, which are linked by a single disulfide bridge. The amino acid sequence of AkCI/1 is homologous to and showed more than 60% sequence similarity with other protease inhibitors isolated earlier from the group of Mimosoideae. AkCI/1 inhibits both chymotrypsin (EC 3.4.21.1) and trypsin (EC 3.4.21.4) in a 1:1M ratio with Ki values of 2.8 × 10(-12)M and 1.87 × 10(-12)M, respectively. The P1-P1' residues for trypsin were identified as Arg68-Ile69 by selective hydrolysis of the inhibitor at this site, with bovine trypsin and human trypsin IV. The cleavage did not affect the inhibition of trypsin, but fully abolished the chymotrypsin inhibitory activity of AkCI/1. This finding together with our studies on competition of the two enzymes for the same combining loop suggests that the same loop has to contain the binding sites for both proteases. The most likely P1 residue of AkCI/1 for chymotrypsin is Tyr67.

Lower homologues of ahpatinin, aspartic protease inhibitors, from a marine Streptomyces sp

Two linear peptides, ahpatinin Ac (1) and ahpatinin Pr (2), were isolated together with the known ahpatinin (i)Bu, pepstatin Ac, pepstatin Pr, and pepsinostreptin from a Streptomyces sp. derived from a deep-sea sediment. The structure of ahpatinin Pr (2) was assigned by interpretation of NMR data and HPLC analysis of the hydrolysate after converting to the DNP-L-Val derivative. During the LCMS analysis of the acid hydrolysate, products arising from the retro-aldol cleavage of the statine and Ahppa units in 2 were observed and could facilitate the determination of the absolute configuration of the statine class of nonproteinogenic amino acids. Both ahpatinin Ac (1) and ahpatinin Pr (2) potently inhibited pepsin and moderately inhibited cathepsin B.

Acantholactam and pre-neo-kauluamine, manzamine-related alkaloids from the Indonesian marine sponge Acanthostrongylophora ingens

Two new manzamine alkaloids, acantholactam (3) and pre-neo-kauluamine (4), were isolated from the marine sponge Acanthostrongylophora ingens along with manzamine A (1) and neo-kauluamine (2). Acantholactam contains a γ-lactam ring N-substituted with a (Z)-2-hexenoic acid moiety and is proposed to be biosynthetically derived from manzamine A by oxidative cleavage of the eight-membered ring. Compound 4 was converted to the dimer 2 during storage, suggesting nonenzymatic dimer formation. Among the four isolated compounds, 1, 2, and 4 showed proteasome inhibitory activity.

Screening of antiviral activities in medicinal plants extracts against dengue virus using dengue NS2B-NS3 protease assay

Dengue virus infects millions of people worldwide and there is no vaccine or anti-dengue therapeutic available. Screening large numbers of medicinal plants for anti-dengue activities is an alternative strategy in order to find the potent therapeutic compounds. Therefore, this study was designed to identify anti-dengue activities in nineteen medicinal plant extracts that are used in traditional medicine. Local medicinal plants Vernonia cinerea, Hemigraphis reptans, Hedyotis auricularia, Laurentia longiflora, Tridax procumbers and Senna angustifolia were used in this study. The highest inhibitory activates against dengue NS2B-NS3pro was observed in ethanolic extract of S. angustifolia leaves, methanolic extract of V. cinerea leaves and ethanol extract of T. procumbens stems. These findings were further verified by in vitro viral inhibition assay. Methanolic extract of V. cinerea leaves, ethanol extract of T. procumbens stems and at less extent ethanolic extract of S. angustifolia leaves were able to maintain the normal morphology of DENV2-infected Vero cells without causing much cytopathic effects (CPE). The percentage of viral inhibition of V. cinerea and T. procumbens extracts were significantly higher than S. angustifolia extract as measured by plaque formation assay and RT-qPCR. In conclusion, The outcome of this study showed that the methanolic extract of V. cinerea leaves and ethanol extract of T. procumbens stems possessed high inhibitory activates against dengue virus that worth more investigation.

Benzophenone C-glucosides and gallotannins from mango tree stem bark with broad-spectrum anti-viral activity

The high mutation rate of RNA viruses has resulted in limitation of vaccine effectiveness and increased emergence of drug-resistant viruses. New effective antivirals are therefore needed to control of the highly mutative RNA viruses. The n-butanol fraction of the stem bark of Mangifera indica exhibited inhibitory activity against influenza neuraminidase (NA) and coxsackie virus 3C protease. Bioassay guided phytochemical study of M. indica stem bark afforded two new compounds including one benzophenone C-glycoside (4) and one xanthone dimer (7), together with eleven known compounds. The structures of these isolated compounds were elucidated on the basis of spectroscopic evidences and correlated with known compounds. Anti-influenza and anti-coxsackie virus activities were evaluated by determining the inhibition of anti-influenza neuraminidase (NA) from pandemic A/RI/5+/1957 H2N2 influenza A virus and inhibition of coxsackie B3 virus 3C protease, respectively. The highest anti-influenza activity was observed for compounds 8 and 9 with IC50 values of 11.9 and 9.2μM, respectively. Compounds 8 and 9 were even more potent against coxsackie B3 virus 3C protease, with IC50 values of 1.1 and 2.0μM, respectively. Compounds 8 and 9 showed weak cytotoxic effect against human hepatocellular carcinoma and human epithelial carcinoma cell lines through MTT assay.

Protease inhibitors from marine actinobacteria as a potential source for antimalarial compound

The study was planned to screen the marine actinobacterial extract for the protease inhibitor activity and its anti- Pf activity under in vitro and in vivo conditions. Out of 100 isolates, only 3 isolates exhibited moderate to high protease inhibitor activities on trypsin, chymotrypsin and proteinase K. Based on protease inhibitor activity 3 isolates were chosen for further studies. The potential isolate was characterized by polyphasic approach and identified as Streptomyces sp LK3 (JF710608). The lead compound was identified as peptide from Streptomyces sp LK3. The double-reciprocal plot displayed inhibition mode is non-competitive and it confirms the irreversible nature of protease inhibitor. The peptide from Streptomyces sp LK3 extract showed significant anti plasmodial activity (IC₅₀: 25.78 µg/ml). In in vivo model, the highest level of parasitemia suppression (≈45%) was observed in 600 mg/kg of the peptide. These analyses revealed no significant changes were observed in the spleen and liver tissue during 8 dpi. The results confirmed up-regulation of TGF-β and down regulation of TNF-α in tissue and serum level in PbA infected peptide treated mice compared to PbA infection. The results obtained infer that the peptide possesses anti- Pf activity activity. It suggests that the extracts have novel metabolites and could be considered as a potential source for drug development.

Application of a cell-based protease assay for testing inhibitors of picornavirus 3C proteases

Proteolytical cleavage of the picornaviral polyprotein is essential for viral replication. Therefore, viral proteases are attractive targets for anti-viral therapy. Most assays available for testing proteolytical activity of proteases are performed in vitro, using heterologously expressed proteases and peptide substrates. To deal with the disadvantages associated with in vitro assays, we modified a cell-based protease assay for picornavirus proteases. The assay is based on the induction of expression of a firefly luciferase reporter by a chimeric transcription factor in which the viral protease and cleavage sites are inserted between the GAL4 binding domain and the VP16 activation domain. Firefly luciferase expression is dependent on cleavage of the transcription factor by the viral protease. This biosafe assay enables testing the effect of compounds on protease activity in cells while circumventing the need for infection. We designed the assay for 3C proteases (3C(pro)) of various enteroviruses as well as of viruses of several other picornavirus genera, and show that the assay is amenable for use in a high-throughput setting. Furthermore, we show that the spectrum of activity of 3C(pro) inhibitor AG7088 (rupintrivir) not only encompasses enterovirus 3C(pro) but also 3C(pro) of foot-and-mouth disease virus (FMDV), an aphthovirus. In contrary, AG7404 (compound 1), an analogue of AG7088, had no effect on FMDV 3C(pro) activity, for which we provide a structural explanation.

Elapid snake venom analyses show the specificity of the peptide composition at the level of genera Naja and Notechis

Elapid snake venom is a highly valuable, but till now mainly unexplored, source of pharmacologically important peptides. We analyzed the peptide fractions with molecular masses up to 10 kDa of two elapid snake venoms—that of the African cobra, N. m. mossambica (genus Naja), and the Peninsula tiger snake, N. scutatus, from Kangaroo Island (genus Notechis). A combination of chromatographic methods was used to isolate the peptides, which were characterized by combining complimentary mass spectrometric techniques. Comparative analysis of the peptide compositions of two venoms showed specificity at the genus level. Three-finger (3-F) cytotoxins, bradykinin-potentiating peptides (BPPs) and a bradykinin inhibitor were isolated from the Naja venom. 3-F neurotoxins, Kunitz/basic pancreatic trypsin inhibitor (BPTI)-type inhibitors and a natriuretic peptide were identified in the N. venom. The inhibiting activity of the peptides was confirmed in vitro with a selected array of proteases. Cytotoxin 1 (P01467) from the Naja venom might be involved in the disturbance of cellular processes by inhibiting the cell 20S-proteasome. A high degree of similarity between BPPs from elapid and viperid snake venoms was observed, suggesting that these molecules play a key role in snake venoms and also indicating that these peptides were recruited into the snake venom prior to the evolutionary divergence of the snakes.

Purification of a protease inhibitor from Dolichos biflorus using immobilized metal affinity chromatography

Plant protease inhibitors (PIs) are generally small proteins which play key roles in regulation of endogenous proteases and may exhibit antifeedant, antifungal, antitumor and cytokine inducing activities. Dolichos biflorus (horse gram) is an unexploited legume, which is rich in nutrients and also has therapeutic importance. It contains a double-headed PI, which is an anti-nutritional factor. As there is no report available on its simultaneous removal and purification in single step, in this study, a double-headed PI active against both trypsin and chymotrypsin was purified from Dolichos biflorus to -14-fold with -84% recovery using an immobilized metal affinity chromatography (IMAC) medium consisting of Zn-alginate beads. The method was single-step, fast, simple, reliable and economical. The purified inhibitor showed a single band on SDS-PAGE corresponding to molecular mass of 16 kDa and was stable over a pH range of 2.0-12.0 and up to a temperature of 100 degrees C for 20 min. The optimum temperature for trypsin and chymotrypsin inhibitor was observed to be 50 degrees C and 37 degrees C, respectively and pH optimum was pH 7.0 and 8.0, respectively. Thus, IMAC using Zn-alginate beads was useful in simultaneous purification and removal of an anti-nutritional factor from horse gram flour in single step. This procedure may also be employed for purification of other plant PIs in one step.

The marine cyanobacterial metabolite gallinamide A is a potent and selective inhibitor of human cathepsin L

A number of marine natural products are potent inhibitors of proteases, an important drug target class in human diseases. Hence, marine cyanobacterial extracts were assessed for inhibitory activity to human cathepsin L. Herein, we have shown that gallinamide A potently and selectively inhibits the human cysteine protease cathepsin L. With 30 min of preincubation, gallinamide A displayed an IC50 of 5.0 nM, and kinetic analysis demonstrated an inhibition constant of ki = 9000 ± 260 M(-1) s(-1). Preincubation-dilution and activity-probe experiments revealed an irreversible mode of inhibition, and comparative IC50 values display a 28- to 320-fold greater selectivity toward cathepsin L than closely related human cysteine cathepsin V or B. Molecular docking and molecular dynamics simulations were used to determine the pose of gallinamide in the active site of cathepsin L. These data resulted in the identification of a pose characterized by high stability, a consistent hydrogen bond network, and the reactive Michael acceptor enamide of gallinamide A positioned near the active site cysteine of the protease, leading to a proposed mechanism of covalent inhibition. These data reveal and characterize the novel activity of gallinamide A as a potent inhibitor of human cathepsin L.

Protease inhibitors from Microcystis aeruginosa bloom material collected from the Dalton Reservoir, Israel

Nine new metabolites, aeruginosins DA495A (1), DA511 (2), DA642A (3), DA642B (4), DA688 (5), DA722 (6), and DA495B (7), microguanidine DA368 (8), and anabaenopeptin DA850 (9), were isolated along with the known micropeptins MZ924, MZ939A, and MZ1019, cyanopeptolins S and SS, microcin SF608, and aeruginazoles DA1497, DA1304, and DA1274 from bloom material of the cyanobacterium Microcystis aeruginosa collected from the Dalton reservoir, Israel, in October 2007. Their structures were elucidated by a combination of various spectroscopic techniques, primarily NMR and MS, while the absolute configurations of the asymmetric centers were determined by Marfey's and chiral-phase HPLC methods. Two of the new aeruginosins, DA511 (1) and DA495A (2), contain a new Choi isomer, (2S,3aS,6S,7aS)-Choi. The structure elucidation and biological activities of the new metabolites are described.

Using a Caesalpinia echinata Lam. protease inhibitor as a tool for studying the roles of neutrophil elastase, cathepsin G and proteinase 3 in pulmonary edema

Acute lung injury (ALI) is characterized by neutrophil infiltration and the release of proteases, mainly elastase (NE), cathepsin G (Cat G) and proteinase 3 (PR3), which can be controlled by specific endogenous inhibitors. However, inhibitors of these proteases have been isolated from different sources, including plants. For this study, CeEI, or Caesalpinia echinata elastase inhibitor, was purified from C. echinata (Brazil-wood) seeds after acetone fractionation, followed by ion exchange and reversed phase chromatographic steps. Characterization with SDS-PAGE, stability assays, amino acid sequencing and alignment with other protein sequences confirmed that CeEI is a member of the soybean Kunitz trypsin inhibitor family. Like other members of this family, CeEI is a 20 kDa monomeric protein; it is stable within a large pH and temperature range, with four cysteine residues forming two disulfide bridges, conserved amino acid residues and leucine-isoleucine residues in the reactive site. CeEI was able to inhibit NE and Cat G at a nanomolar range (with K(i)s of 1.9 and 3.6 nM, respectively) and inhibited PR3 within a micromolar range (K(i) 3.7 μM), leading to hydrolysis of specific synthetic substrates. In a lung edema model, CeEI reduced the lung weight and pulmonary artery pressure until 180 min after the injection of zymosan-activated polymorphonuclear neutrophils. In experiments performed in the presence of a Cat G and PR3, but not an NE inhibitor, lung edema was reduced only until 150 min and pulmonary artery pressure was similar to that of the control. These results confirm that NE action is crucial to edema establishment and progression. Additionally, CeEI appears to be a useful tool for studying the physiology of pulmonary edema and provides a template for molecular engineering and drug design for ALI therapy.

Assessing activity and inhibition of Middle East respiratory syndrome coronavirus papain-like and 3C-like proteases using luciferase-based biosensors

Middle East respiratory syndrome coronavirus (MERS-CoV) is associated with an outbreak of more than 90 cases of severe pneumonia with high mortality (greater than 50%). To date, there are no antiviral drugs or specific therapies to treat MERS-CoV. To rapidly identify potential inhibitors of MERS-CoV replication, we expressed the papain-like protease (PLpro) and the 3-chymotrypsin-like protease (3CLpro) from MERS-CoV and developed luciferase-based biosensors to monitor protease activity in cells. We show that the expressed MERS-CoV PLpro recognizes and processes the canonical CoV-PLpro cleavage site RLKGG in the biosensor. However, existing CoV PLpro inhibitors were unable to block MERS-CoV PLpro activity, likely due to the divergence of the amino acid sequence in the drug binding site. To investigate MERS-CoV 3CLpro activity, we expressed the protease in context with flanking nonstructural protein 4 (nsp4) and the amino-terminal portion of nsp6 and detected processing of the luciferase-based biosensors containing the canonical 3CLpro cleavage site VRLQS. Importantly, we found that a small-molecule inhibitor that blocks replication of severe acute respiratory syndrome (SARS) CoV and murine CoV also inhibits the activity of MERS-CoV 3CLpro. Overall, the protease expression and biosensor assays developed here allow for rapid evaluation of viral protease activity and the identification of protease inhibitors. These biosensor assays can now be used to screen for MERS-CoV-specific or broad-spectrum coronavirus PLpro and 3CLpro inhibitors.