Purification and biochemical characterisation of a novel protease streblin

Plant-derived rennet: research progress, novel strategies for their isolation, identification, mechanism, bioactive peptide generation, and application in cheese manufacturing

Rennet, an aspartate protease found in the stomach of unweaned calves, effectively cuts the peptide bond between Phe105-Met106 in κ-casein, hydrolyzing the casein micelles to coagulate the milk and is a crucial additive in cheese production. Rennet is one of the most used enzymes of animal origin in cheese making. However, using rennet al.one is insufficient to meet the increasing demand for cheese production worldwide. Numerous studies have shown that plant rennet can be an alternative to bovine rennet and exhibit a good renneting effect. Therefore, it is crucial and urgent to find a reliable plant rennet. Based on our team's research on rennet enzymes of plant origin, such as from Dregea sinensis Hemsl. and Moringa oleifer Lam., for more than ten years, this paper reviews the relevant literature on rennet sources, isolation, identification, rennet mechanism, functional active peptide screening, and application in cheese production. In addition, it proposes the various techniques for targeted isolation and identification of rennet and efficient screening of functionally active peptides, which show excellent prospects for development.

Plant Milk-Clotting Enzymes for Cheesemaking

The reduced availability and the increasing prices of calf rennet, coupled to the growing global demand of cheese has led, worldwide, to explore alternative clotting enzymes, capable to replace traditional rennet, during the cheesemaking. In addition, religious factors and others related to the vegetarianism of some consumers, have led to alternative rennet substitutes. Nowadays, several plant-derived milk-clotting enzymes are available for cheesemaking technology. Many efforts have also been made to compare their effects on rheological and sensory properties of cheese to those arising from animal rennet. However, vegetable clotting enzymes are still partially suitable for cheesemaking, due to excessive proteolytic activity, which contribute to bitter flavor development. This review provides a literature overview of the most used vegetable clotting enzymes in cheese technology, classified according to their protease class. Finally, clotting and proteolytic activities are discussed in relation to their application on the different cheesemaking products.

Potential Biological Activities of Peptides Generated during Casein Proteolysis by Curly Kale (Brassica oleracea L. var. sabellica L.) Leaf Extract: An In Silico Preliminary Study

This study is a brief report on the proteolytic activity of curly kale leaf extract against casein. Casein degradation products and an in silico analysis of the biological activity of the peptides obtained was performed. The efficiency of casein hydrolysis by curly kale extract was determined using SDS-PAGE and by peptide concentration determination. The pattern of the enzymatic activity was determined by MALDI-TOF MS analysis. The results showed that α- and β-casein were more resistant to curly kale extract hydrolysis, whereas κ-casein was absent in the protein profile after 8 h of proteolysis, and all casein fractions were completely hydrolyzed after 24 h of incubation. Based on sequence analysis, seven peptides were identified, with molecular mass in the range of 1151-3024 Da. All the peptides were products of β-casein hydrolysis. The identified amino acid sequences were analyzed in BIOPEP, MBPDB, and FeptideDB databases in order to detect the potential activities of the peptides. In silico analysis suggests that the β-casein-derived peptides possess sequences of peptides with ACE inhibitory, antioxidant, dipeptidyl peptidase IV inhibitory, antithrombotic, immunomodulatory, and antiamnesic bioactivity. Our study was first to evaluate the possibility of applying curly kale leaf extract to generate biopeptides through β-casein hydrolysis.

Advances in research on calf rennet substitutes and their effects on cheese quality

Milk coagulation is an important step in cheese production, and milk-clotting enzymes (MCEs) play a major role in this process. Calf rennet is the most widely used MCE in the cheese industry. The use of calf rennet substitutes is becoming necessary due to the limited availability of calf rennet and the increase in cheese consumption. The objective of this review is to summarize the latest findings on calf rennet substitutes (animal MCEs, plant-derived MCEs, recombinant MCEs and microbial MCEs) and their application in cheese production. Special emphasis has been placed on aspects of the effects of these substitutes on hydrolysis, functional peptides, cheese variety and cheese yield. The advantages and disadvantages of different calf rennet substitutes are discussed, in which microbial MCEs have the advantages of less expensive production, greater biochemical diversity, easier genetic modification, etc. In particular, some of these MCEs have suitable characteristics for cheese production and are considered to be the most potential calf rennet substitutes. Moreover, challenges and future perspectives are presented to provide inspiration for the development of excellent calf rennet substitutes.

Characterization of a recombinant sucrose isomerase and its application to enzymatic production of isomaltulose

OBJECTIVE

To characterize a recombinant isomerase that can catalyze the isomerization of sucrose into isomaltulose and investigate its application for the enzymatic production of isomaltulose.

RESULTS

A sucrose isomerase gene from Erwinia sp. Ejp617 was synthesized and expressed in Escherichia coli BL21(DE3). The enzymatic characterization revealed that the optimal pH and temperature of the purified sucrose isomerase were 6.0 and 40 °C, respectively. The enzyme activity was slightly activated by Mn²⁺and Mg²⁺, but partially inhibited by Ca²⁺, Ba²⁺, Cu²⁺, Zn²⁺ and EDTA. The kinetic parameters of K_m and V_max for sucrose were 69.28 mM and 118.87 U/mg, respectively. The time course showed that 240.9 g/L of isomaltulose was produced from 300 g/L of sucrose, and the yield reached 80.3% after bioreaction for 180 min.

CONCLUSIONS

This recombinant enzyme showed excellent capability for biotransforming sucrose to isomaltulose at the substrate concentration of 300 g/L. Further investigations should be carried out focusing on selection of suitable heterologous expression system with the aim to improve its expression level.

Structural and biochemical characterization of a novel thermophilic Coh01147 protease

Proteases play an essential role in living organisms and represent one of the largest groups of industrial enzymes. The aim of this work was recombinant production and characterization of a newly identified thermostable protease 1147 from thermophilum indigenous Cohnella sp. A01. Phylogenetic tree analysis showed that protease 1147 is closely related to the cysteine proteases from DJ-1/ThiJ/PfpI superfamily, with the conserved catalytic tetrad. Structural prediction using MODELLER 9v7 indicated that protease 1147 has an overall α/β sandwich tertiary structure. The gene of protease 1147 was cloned and expressed in Escherichia coli (E. coli) BL21. The recombinant protease 1147 appeared as a homogenous band of 18 kDa in SDS-PAGE, which was verified by western blot and zymography. The recombinant protein was purified with a yield of approximately 88% in a single step using Ni-NTA affinity chromatography. Furthermore, a rapid one-step thermal shock procedure was successfully implemented to purify the protein with a yield of 73%. Using casein as the substrate, K_m, and k_cat, k_cat/K_m values of 13.72 mM, 3.143 × 10⁻³ (s^-1), and 0.381 (M^-1 S^-1) were obtained, respectively. The maximum protease activity was detected at pH = 7 and 60°C with the inactivation rate constant (kin) of 2.10 × 10–3 (m^-1), and half-life (t_1/2) of 330.07 min. Protease 1147 exhibited excellent stability to organic solvent, metal ions, and 1% SDS. The protease activity was significantly enhanced by Tween 20 and Tween 80 and suppressed by cysteine protease specific inhibitors. Docking results and molecular dynamics (MD) simulation revealed that Tween 20 interacted with protease 1147 via hydrogen bonds and made the structure more stable. CD and fluorescence spectra indicated structural changes taking place at 100°C, very basic and acidic pH, and in the presence of Tween 20. These properties make this newly characterized protease a potential candidate for various biotechnological applications.

A contradictory action of procoagulant ficin by a fibrinolytic serine protease from Egyptian Ficus carica latex

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We purified a serine protease from Ficus carica latex.

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Serine protease had a high tendency to hydrolyze fibrinogin.

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Serine protease inhibited blood coagulation.

Ficus carica is one of the most popular and edible plants. Its trees emanate latex of high medical importance. The well-studied procoagulant effect of ficin is a hallmark of this latex which protrudes an interesting question of how can the plant control this effect? In the present work, we purified and characterized a serine protease (FPIII) with fibrinolytic activity from F. carica latex and study the anticoagulant character of the latex. FPIII was inhibited by PMSF and its molecular weight was 48 kDa. The optimum pH and temperature of FPIII were detected at 8.5 and 60 °C, respectively. The activation energy of FPIII was 7 kcal/mol and was thermal stable up to 60 °C. FPIII tended to hydrolyze different protein substrates and showed a good catalytic efficiency (K_cat/K_m). The anticoagulant effects and fibrinogenolytic activities of latex crude extract and FPIII were detected, which controls the procoagulant effect of ficin.

Clotting Properties of Onopordum tauricum (Willd.) Aqueous Extract in Milk of Different Species

Plant proteases used in cheesemaking are easily available and could increase the acceptability of cheeses, otherwise hindered by ethical issues (e.g., religions, dietary habits, aversion to genetically engineered food and food ingredients). The milk clotting potential of Onopordum tauricum (Willd.) aqueous extract as an alternative to animal rennet was assessed for the first time in milk of different species (ewe, goat, cow). Among the aerial anatomical parts, i.e., receptacle, leaves, stems, and flowers, only the latter ones showed clotting properties. A response surface methodology (RSM) was used to explore the effects of three independent variables (temperature, pH, volume of coagulant) on the milk clotting activity (MCA) of the flower extract. A second-order polynomial model adequately described the experimental data and predicted a temperature value of 55 °C, a pH value of 4.9–5.7, and a volume of coagulant of 300–500 μL (added to 5 mL of milk) as optimal conditions to maximize the MCA. At a 35 °C temperature and natural milk pH of 6.7–6.8, the estimated MCA of the O. tauricum extract was 72–87, 69–86, and 75–151, in goat’s, ewe’s, and cow’s milk, respectively. In comparison, the MCA of calf rennet was 5.4–4.9, 3.3–14.7, and 4.9–16.7 times higher than that of the plant extract in goat’s, ewe’s, and cow’s milk, respectively.

Three phase partitioning to concentrate milk clotting proteases from Wrightia tinctoria R. Br and its characterization

Wrightia tinctoria stem proteases were partially purified for the first time through a non-chromatographic technique, three phase partitioning (TPP), to concentrate the milk clotting proteases. Various parameters like salt and solvent concentration that affect the partitioning of the protease were examined. Maximum recovery and purification fold of the protease activity were found in the interfacial phase (IP) with 60% ammonium sulphate and 1:1 crude enzyme to t-butanol. Optimum pH and temperature of the enzyme fraction were found to be 7.5 and 50 °C respectively. Inhibition studies revealed its serine nature. Non-denaturing PAGE, Zymography and 2D PAGE of IP revealed presence of three different caseinolytic proteases of molecular weights 95.62 kDa, 91.11 kDa and 83.23 kDa with pI 3.89, 5.45 and 5.43 respectively. Both aqueous and lyophilized form of IP were remarkably stable retaining complete activity at 4 °C for 3 weeks. Electrophoretic analysis of casein hydrolysate by IP at different incubation time indicated a time dependent substrate subunit specificity with hydrolysis of κ-casein commencing after 10 min followed by α and β caseins. This pattern was found similar to that by commercial vegetable coagulant, Enzeco®. Study details the effectiveness of TPP concentrated W. tinctoria proteases as a vegetable coagulant alternative in cheese making.

High-level expression, purification, and enzymatic characterization of a recombinant Aspergillus sojae alkaline protease in Pichia pastoris

An alkaline protease (Ap) was cloned from Aspergillus sojae GIM3.33 via RT-PCR technique. A truncated Ap without the signal peptide was successfully expressed in the Pichia pastoris KM71 strain. The following describes the optimal process conditions for the recombinant engineering of a strain expressing a recombinant Ap (rAp) in a triangular flask: inoculum concentration OD₆₀₀ value 20.0 in 40 mL working volume (in 500 mL flasks), methanol addition (1.0%; volume ratio), 0.02% biotin solution (60 μL), and YNB primary concentration (13.0 g/L). Under these conditions, the protease activity of rAp in the fermentation broth reached 400.4 ± 40.5 U/mL after induction for three days. The rAp was isolated and purified, and its enzymatic characteristics were tested. Its optimal pH was 10.0, and it remained stable in a pH range of 7.0-10.0. Its optimal temperature was 45 °C and it retained >50% activity at 40 °C for 60 min. The rAp activity was significantly inhibited by PMSF, Zn²⁺ and Fe²⁺ and the rAp had a broad substrate specificity for natural proteins and synthetic peptide substrates, and preferred substrates at P1 position with large hydrophobic side-chain groups. Compared to Papain (8.7%) and Alcalase (12.2%), the degree of hydrolysis of rAp to soy protein isolate was 16.5%; therefore, rAp was a good candidate for the processing of food industry byproducts.

Three phase partitioning, a scalable method for the purification and recovery of cucumisin, a milk-clotting enzyme, from the juice of Cucumis melo var. reticulatus

Cucumisin [EC 3.4.21.25] was first purified from Cucumis melo var. reticulatus juice by three-phase partitioning (TPP). Optimum purification parameters of the TPP system were determined as 60% ammonium sulfate saturation with 1.0:1.25 ratio of crude extract: t-butanol at pH and temperature of 8.0 and 20°C, respectively. Cucumisin was purified with 4.61 purification fold and 156% activity recovery. The molecular weight of the recovered cucumisin was determined as 68.4kDa and its isoelectric point is 8.7. Optimum pH and temperature of cucumisin were pH 9.0 and 60-70°C, respectively. The protease was very stable at 20-70°C and a pH range of 2.0-12.0. Km and Vmax constants were 2.24±0.22mgmL^-1 and 1048±25μ Mmin^-1, respectively. The enzyme was stable against numerous metal ions and its activity was highly enhanced by Ca²⁺, Mg²⁺, and Mn⁺². Cucumisin activity was 2.35-folds increased in the presence of 5mM of CaCl₂. It was inactivated by Co²⁺, Cd²⁺, Zn²⁺ and Fe²⁺ and dramatically by PMSF. Cucumisin milk-clotting activity was highly stable when stored under freezing (-20°C) compared at 4°C and 25°C. Finally, TPP revealed to be a useful strategy to concentrate and purify cucumisin for its use as a milk-clotting enzyme for cheese-making.

Antibacterial serine protease from Wrightia tinctoria: Purification and characterization

A serine protease was purified from the leaves of Wrightia tinctoria by sequential flow through method comprising screening, optimization, ammonium sulfate precipitation, gel filtration and ion exchange column chromatography. The yield and purification fold obtained were 11.58% and 9.56 respectively. A single band of serine protease was visualized on SDS-PAGE and 2-D gel electrophoretic analyses were revealed with the molecular mass of 38.5 kDa. Serine protease had an optimum pH of 8.0 and was stable at 45°C with high relative protease activity. The addition of metal ions such as Mg2+ and Mn2+ exhibits a high relative activity. Serine protease had a potent antibacterial activity against both Gram-positive and Gram-negative bacteria. A 10 μg/ml of serine protease was tested against S. aureus, M. luteus, P. aeruginosa and K. pneumoniae which had 21, 20, 18 and 17 mm of zone of inhibition respectively. Serine protease from W. tinctoria degrades the peptidoglycan layer of bacteria which was visualized by transmission electron microscopic analysis.

Effect of extraction pH on techno-functional properties of crude extracts from wild cardoon (Cynara cardunculus L.) flowers

In the present paper, techno-functional properties of rennet derived from C. cardunculus, prepared at various pH (from 3 to 6), were investigated. It was found that the extract prepared at pH 3 had the best milk-clotting properties (MCA/PA ratio). It presented also the highest enzyme content, determined by densitometry analysis on 1D and 2D gels electrophoresis. Formation of milk gels produced by the extracts and chymosin was monitored using dynamic rheology and turbiscan. It can be assumed that by lowering rennet pH, milk pH decreases, causing a significant increase of curd firmness and both elastic (G') and viscous (G″) moduli. Results obtained by turbiscan showed similar ΔBS values of gels produced, after 2h, by chymosin and the crude extract at pH 3. In conclusion, C. cardunculus extract prepared at low pH has the potential to be employed as an efficient milk-clotting agent in the production of dairy products.

Partial Characterization of the Proteolytic Properties of an Enzymatic Extract From "Aguama" Bromelia pinguin L. Fruit Grown in Mexico

Plant proteases are capable of performing several functions in biological systems, and their use is attractive for biotechnological process due to their interesting catalytic properties. Bromelia pinguin (aguama) is a wild abundant natural resource in several regions of Central America and the Caribbean Islands but is underutilized. Their fruits are rich in proteases with properties that are still unknown, but they represent an attractive source of enzymes for biotechnological applications. Thus, the proteolytic activity in enzymatic crude extracts (CEs) from wild B. pinguin fruits was partially characterized. Enzymes in CEs showed high proteolytic activity at acid (pH 2.0-4.0) and neutral alkaline (pH 7.0-9.0) conditions, indicating that different types of active proteases are present. Proteolytic activity inhibition by the use of specific protease inhibitors indicated that aspartic, cysteine, and serine proteases are the main types of proteases present in CEs. Activity at pH 3.0 was stable in a broad range of temperatures (25-50 °C) and retained its activity in the presence of surfactants (SDS, Tween-80), reducing agents (DTT, 2-mercapoethanol), and organic solvents (methanol, ethanol, acetone, 2-propanol), which suggests that B. pinguin proteases are potential candidates for their application in brewing, detergent, and pharmaceutical industries.

Expression, purification, refolding and in vitro recovery of active full length recombinant human gelatinase MMP-9 in Escherichia coli

Human gelatinase (MMP-9) is a member of matrix metalloproteinases family (MMPs), which has been associated with malignant tumor progression and metastasis by matrix degradation. Herein, active full length recombinant human MMP-9 (amino acid residues 107-707) has been expressed in the form of inclusion bodies in Escherichia coli BL21, using pET21a vector. Solubilization of inclusion bodies was carried out in Tris-HCl buffer with 6 M urea, and refolding was performed using dilution and urea gradient methods. Tris-HCl buffer with 5 mM CaCl2 and 1 μM ZnCl2 at pH 7.8 was used as a refolding buffer. Analysis of the structure by fluorescence and far-UV circular dichroism showed a well-formed structure by urea gradient method. Kinetic parameters in refolding conditions of rhMMP-9 were also analyzed, depicting increase in the enzyme's activity without any aggregation.

Development of a label-free SPR sensor for detection of matrixmetalloproteinase-9 by antibody immobilization on carboxymethyldextran chip

Surface plasmon resonance (SPR) immunosensor has been widely utilized for monitoring antigen-antibody interactions. The sensor measures changes of refractive index upon binding of analyte molecules to specific ligand immobilized on the sensor chip. This effort reports development of SPR immunosensor for real-time and label-free detection of recombinant human matrix metalloproteinases-9 (MMP-9), which has been associated with malignant tumor progression and metastasis by matrix degradation. MMP-9 was expressed in Escherichia coli BL21 and purified by Ni-NTA agarose column. CMD 50 D was activated by EDC/NHS for immobilization of monoclonal anti-MMP-9. Atomic force microscopy images showed uniform distribution of anti-MMP-9 over the sensor chip. Equilibrium constant (KD), maximum binding capacity (Rmax) and ∆Gb values for interaction of MMP-9 and anti-MMP-9 were 0.4nM, 680 µRIU and -53.51kJ/mol, respectively. Concentration of MMP-9 in saliva samples was determined, with linearity in the range of 10-200ng/mL. The limit of detection was found to be 8pg/mL, being lower than most of the previously reported techniques.

Purification and characterization of alkaline-thermostable protease enzyme from Pitaya (Hylocereus polyrhizus) waste: a potential low cost of the enzyme

The thermoalkaline protease enzyme from pitaya (Hylocereus polyrhizus) waste was purified by a factor of 221.2 with 71.3% recovery using ammonium sulphate precipitation, gel filtration, and cation exchange chromatography. Gel filtration chromatography together with sodium dodecyl sulphate gel electrophoresis (SDS-PAGE) revealed that the enzyme is monomeric with a molecular weight of 26.7 kDa. The apparent K_m and V_max of the protease were 2.8 mg/mL and 31.20 u/min, respectively. The optimum pH and temperature were 8.0 and 70°C. The enzyme was highly active and stable over a wide pH range (from pH 3.0 to pH 11.0 with the optimum activity at pH 8.0). The protease has broad specificity toward azocasein, casein, hemoglobin, and gelatine. Activity of the enzyme was inhibited by Fe²⁺ and Zn²⁺, while protease activity was increased in the presence of Ca²⁺ and Mg²⁺ and Cu²⁺ by factors of 125%, 110%, and 105%, respectively. The alkaline protease showed extreme stability toward surfactants and oxidizing agent. The purified protease exhibited extreme stability in the presence of organic solvents and inhibitors. In addition, the enzyme was relativity stable toward organic solvents and chelating agents, such as ethylenediaminetetraacetic acid (EDTA). The enzyme, derived from pitaya peel, possesses unique characteristics and could be used in various industrial and biotechnological applications.

Identification of folding intermediates of streblin, the most stable serine protease: biophysical analysis

Streblin, a serine proteinase from plant Streblus asper, has been used to investigate the conformational changes induced by pH, temperature, and chaotropes. The near/far UV circular dichroism activities under fluorescence emission spectroscopy and 8-aniline-1-naphthalene sulfonate (ANS) binding have been carried out to understand the unfolding of the protein in the presence of denaturants. Spectroscopic studies reveal that streblin belongs to the α+β class of proteins and exhibits stability towards chemical denaturants, guanidine hydrochloride (GuHCl). The pH-induced transition of this protein is noncooperative for transition phases between pH 0.5 and 2.5 (midpoint, 1.5) and pH 2.5 and 10.0 (midpoint, 6.5). At pH 1.0 or lower, the protein unfolds to form acid-unfolded state, and for pH 7.5 and above, protein turns into an alkaline denatured state characterized by the absence of ANS binding. At pH 2.0 (1 M GuHCl), streblin exists in a partially unfolded state with characteristics of a molten globule state. The protein is found to exhibit strong and predominant ANS binding. In total, six different intermediate states has been identified to show protein folding pathways.

Anti-hepatitis B virus constituents from the stem bark of Streblus asper

Seven compounds, (7'S,8'S)-trans-streblusol A, (7'R,8'S)-erythro-streblusol B, (7'S,8'S)-threo-streblusol B, 8'R-streblusol C, streblusquinone, (8R,8'R)-streblusol D, and streblusol E, along with 15 known compounds (8-22) were isolated from the n-butanol-soluble part of the MeOH extract of stem bark of Streblus asper. Their structures were elucidated through application of extensive spectroscopic methods, including ESI-MS and 2D NMR spectroscopy (HMQC and HMBC). The stereochemistry at the chiral centers was determined using CD spectra, as well as analyses of coupling constants and optical rotation data. The isolated lignans and allylbenzene derivatives were evaluated for their anti-HBV activities in vitro using the HBV transfected Hep G2.2.15 cell line. The most active compounds, magnolol and 9-β-xylopyranosyl-isolariciresinol, exhibited significant anti-HBV activities with IC(50) values of 2.03 and 6.58μM for secretion of HBsAg, with no cytotoxicity, and of 3.76 and 24.86μM for secretion of HBeAg, with no cytotoxicity.

Water-soluble Constituents of the Heartwood of Streblus asper

A new lignan, (7′ R,8′ R)- threo-strebluslignanol-2- O-β-D-glucopyranoside, along with 8 known compounds (2–9) were isolated from the water-soluble part of the MeOH extract of the heartwood of Streblus asper. Their structures were elucidated through various spectroscopic methods, including 1D NMR (1H NMR, 13C NMR), 2D NMR (HMQC, HMBC, and NOESY), and HRMS. The stereochemistry at the chiral centers was determined using the CD spectrum, as well as analyses of coupling constants and optical rotation data. In the preliminary bioassay, the isolated compounds did not show anti-HBV activities in vitro using the HBV transfected HepG2.2.15 cell line.

Enzymatic production of 5'-inosinic acid by a newly synthesised acid phosphatase/phosphotransferase

5'-Nucleotides including 5'-inosinic acid have characteristic taste and important application in various foods as flavour potentiators. The selective nucleoside acid phosphatase/phosphotransferase (AP/PTase) can catalyse the synthesis of 5'-nucleotides by transfer of phosphate groups. In this study, a 747-bp gene encoding AP/PTase from Escherichia blattae was synthesised. After expression, the recombinant AP/PTase was purified using nickel-NTA. The optimal temperature and pH of this enzyme were 30°C and 5.0, respectively. The activity was partially inhibited by metal ions such as Hg(2+), Ag(+) and Cu(2+), but not by chelating reagents such as EDTA. The values of K(m) and V(max) for inosine were 40 mM and 3.5 U/mg, respectively. Using this purified enzyme, 16.83 mM of 5'-IMP was synthesised from 37 mM of inosine and the molar yield reached 45.5%. Homology modelling and docking simulation were discussed.

Anti-HBV activities of Streblus asper and constituents of its roots

The extracts from leaves, heartwood, barks and roots of the Streblus asper were investigated for anti-HBV activities, separately. The results suggested that the MeOH extracts of the heartwood, barks, and roots exhibited good anti-HBV activities. Further investigations displayed that ethyl acetate and n-butanol soluble parts of their MeOH extracts showed more significant anti-HBV activities. Moreover, a new lignan, together with 11 known compounds, was isolated from n-butanol-soluble part of MeOH extract of the roots of S. asper. The structures were elucidated by spectroscopic methods, including 1D NMR ((1)H NMR, (13)C NMR), 2D NMR (HMQC, HMBC) and HR-EI-MS experiments. Compounds 1-3 were evaluated for their anti-HBV activities. Honokiol showed significant anti-HBV activity with IC(50) values of 3.14μM and 4.74μM for HBsAg and HBeAg with no cytotoxicity respectively, while lamivudine (3TC, positive control) exhibited weak anti-HBV activity with IC(50) values of 11.81μM and 25.80μM for HBsAg and HBeAg respectively.

Neriifolin S, a dimeric serine protease from Euphorbia neriifolia Linn.: Purification and biochemical characterisation

A dimeric serine protease Neriifolin S of molecular mass 94kDa with milk clotting activity has been purified from the latex of Euphorbia neriifolia by anion exchange and size-exclusion chromatography. It hydrolyses peptidyl substrates l-Ala-pNA with highest affinity (K_m of 0.195mM) and physiological efficiency (K_cat/K_m of 144.5mMs). Enzyme belongs to the class of neutral proteases with pI value of 6.8, optimal proteolytic activity displayed at pH 9.5 and temperature 45°C. Its proteolytic activity is strongly stimulated in the presence of Ca⁺² ions and exclusively inhibited by serine protease inhibitors. Enzyme is fairly stable toward chemical denaturants, pH and temperature. The apparent T_m, was found to be 65°C. Thermal inactivation follow first order kinetics with activation energy (Ea), activation enthalpy (ΔH∗), free energy change (ΔG∗) and entropy (ΔS∗) of 27.54kJmol^-1, 24.89kJmol^-1, -82.34kJmol^-1 and 337.20Jmol^-1K^-1.