Improved Expression of a Thermostable GH18 Bacterial Chitinase in Two Different Escherichia coli Strains and Its Potential Use in Plant Protection and Biocontrol of Phytopathogenic Fungi

Chitinases are enzymes that can break down chitin, a major component of the exoskeleton of insects and fungi. This feature makes them potential biopesticides in agriculture since they are considered a safe and environmentally friendly alternative to synthetic pesticides. In this work, we performed a comparative study between two different bacterial expression strains to produce a recombinant chitinase with improved stability. Escherichia coli strains Origami B and BL21 (DE3) were selected for their distinct cytosolic environment to express BhChitA chitinase of Bacillus halodurans C-125 and to investigate the role of disulfide bond formation and proper folding on its stability and activity. Expression of the recombinant BhChitA in bacterial strain containing oxidative cytosol (Origami B) improved its activity and stability. Although both expression systems have comparable biochemical properties (temperature range 20-80 °C and pH spectrum 3-10), BhChitA expressed in Origami strain seems more stable than expressed in BL21. Furthermore, the optimal expression conditions of the recombinant BhChitA has been carried out at 30 °C during 6 h for the Origami strain, against 20 °C during 2 h for BL21. On the other hand, no significant differences were detected between the two enzymes when the effect of metal ions was tested. These findings correlate with the analysis of the overall structure of BhChitA. The model structure permitted to localize disulfide bond, which form a stable connection between the substrate-binding residues and the hydrophobic core. This link is required for efficient binding of the chitin insertion domain to the substrate. BhChitA exhibited in vitro antifungal effect against phytopathogenic fungi and suppressed necrosis of Botrytis cinerea on detached tomato leaves. In vitro assays showed the influence of BhChitA on growth suppression of Botrytis cinerea (53%) Aspergillus niger (65%), Fusarium graminearum (25%), and Fusarium oxysporum (34%). Our results highlight the importance of the bacterial expression system with oxidative cytosol in producing promising biopesticides that can be applied for post-harvest processing and crop protection.

Enhancement of Aeribacillus pallidus strain VP3 lipase catalytic activity through optimization of medium composition using Box-Behnken design and its application in detergent formulations

Lipases are hydrolytic enzymes owing much importance in industrial applications. These enzyme-based detergents are ecofriendly and produce a wastewater with low level of COD (chemical oxygen demand). In the present work, a novel halophilous, thermoalkaline, and detergent-tolerant lipase produced by a newly isolated Aeribacillus pallidus strain VP3 was studied. Considerable interest has been given to this lipase by the improvement of its catalytic activity through the optimization of the pH, the (C/N) ratio, and the inoculum size, using the response surface methodology based on the Box-Behnken design of experiments. A total of 16 experiments were conducted, and the optimized pH, (C/N) ratio, and inoculum size were 10, 1, and 0.3, respectively. The results of the analysis of variance (ANOVA) test indicated that the established model was significant (p value < 0.05). The optimization of the production conditions leads to 2.83-fold of increase in the catalytic activity calculated as the ratio of the activity obtained after optimization (68 U) and the initial activity before optimization (24 U). All in all, the lipase of Aeribacillus pallidus could be considered as a potential candidate to be incorporated in detergent formulations since it shows a good stability towards detergents and wash performance.

Purification, biochemical and molecular study of lipase producing from a newly thermoalkaliphilic Aeribacillus pallidus for oily wastewater treatment

Treatment of oily wastewater is constantly a challenge; biological wastewater treatment is an effective, cheap and eco-friendly technology. A newly thermostable, haloalkaline, solvent tolerant and non-induced lipase from Aeribacillus pallidus designated as GPL was purified and characterized of biochemical and molecular study for apply in wastewater treatment. The GPL showed a maximum activity at 65°C and pH 10 after 22 h of incubation, with preference to TC4 substrates. Pure enzyme was picked up after one chromatographic step. It displayed an important resistance at high temperature, pH, NaCl, at the presence of detergents and organic solvents. In fact, GPL exhibited a prominent stability in wide range of organic solvents at 50% (v/v) concentration for 2 h of incubation. The efficiency of the GPL in oil wastewater hydrolysis was established at 50°C for 1 h, the oil removal efficiency was established at 96, 11% and the oil biodegradation was confirmed through fourier transform infrared (FT-IR) spectroscopy. The gene that codes for this lipase was cloned and sequenced and its open reading frame encoded 236 amino acid residues. The deduced amino acids sequence of the GPL shows an important level of identity with Geobacillus lipases.

Antibacterial, antifungal and anticoagulant activities of chicken PLA2 group V expressed in Pichia pastoris

Secretory class V phospholipase A2 (PLA2-V) has been shown to be involved in inflammatory processes in cellular studies, but the biochemical and physical properties of this important enzyme have been unclear. As a first step towards understanding the structure, function and regulation of this PLA2, we report the expression and characterization of PLA2-V from chicken (ChPLA2-V). The ChPLA2-V cDNA was synthesized from chicken heart polyA mRNA by RT-PCR, and an expression construct containing the PLA2 was established. After expression in Pichia pastoris cells, the active enzyme was purified. The purified ChPLA2-V protein was biochemically and physiologically characterized. The recombinant ChPLA2-V has an absolute requirement for Ca²⁺ for enzymatic activity. The optimum pH for this enzyme is pH 8.5 in Tris-HCl buffer with phosphatidylcholine as substrate. ChPLA2-V was found to display potent Gram-positive and Gram-negative bactericidal activity and antifungal activity in vitro. The purified enzyme ChPLA2-V with much stronger anticoagulant activity compared with the intestinal and pancreatic chicken PLA2-V was approximately 10 times more active. Chicken group V PLA2, like mammal one, may be considered as a future therapeutic agents against fungal and bacterial infections and as an anticoagulant agent.

Preparation of the Full Set of Recombinant Mouse- and Human-Secreted Phospholipases A2

A family of 14-20kDa, disulfide-rich, calcium-dependent secreted phospholipases A₂ (sPLA₂s) that release fatty acids from the sn-2 position of glycerophospholipids can be found in mammals. They have a diverse array of tissue distribution and biological functions. In this chapter we provide detailed protocols for production of nearly all of the mouse and human sPLA₂s mainly by expression in bacteria and in vitro refolding or by expression in insect cells. High-resolution mass spectrometry and enzymatic assays were, respectively, used to show that all disulfides are formed and that the enzymes are active, strongly suggesting that each sPLA₂ was prepared in the structurally native form. The availability of these proteins has allowed kinetic studies to be carried out, to prepare highly selective antisera, to screen for selective inhibitors, to study receptor binding, and to study the action of each enzyme on mammalian cell membranes and their in vivo biological roles.

Efficient heterologous expression of Fusarium solani lipase, FSL2, in Pichia pastoris, functional characterization of the recombinant enzyme and molecular modeling

The gene coding for a lipase of Fusarium solani, designated as FSL2, shows an open reading frame of 906bp encoding a 301-amino acid polypeptide with a molecular mass of 30kDa. Based on sequence similarity with other fungal lipases, FSL2 contains a catalytic triad, consisting of Ser144, Asp198, and His256. FSL2 cDNA was subcloned into the pGAPZαA vector containing the Saccharomyces cerevisiae α-factor signal sequence and this construct was used to transform Pichia pastoris and achieve a high-level extracellular production of a FSL2 lipase. Maximum lipase activity was observed after 48h. The optimum activity of the purified recombinant enzyme was measured at pH 8.0-9.0 and 37°C. FSL2 is remarkably stable at alkaline pH values up to 12 and at temperatures below 40°C. It has high catalytic efficiency towards triglycerides with short to long chain fatty acids but with a marked preference for medium and long chain fatty acids. FSL2 activity is decreased at sodium taurodeoxycholate concentrations above the Critical Micelle Concentration (CMC) of this anionic detergent. However, lipase activity is enhanced by Ca²⁺ and inhibited by EDTA or Cu²⁺ and partially by Mg²⁺ or K⁺. In silico docking of medium chain triglycerides, monogalctolipids (MGDG), digalactolipids (DGDG) and long chain phospholipids in the active site of FSL2 reveals structural solutions.

Heterologous overexpression and biochemical characterization of the (galactophospho)lipase from Fusarium solani in Pichia pastoris that is expressed in planta

High-level extracellular production of Fusarium solani (galactophospho)lipase, named FSL, was achieved using a Pichia pastoris X33 expression system. The (galactophospho) lipase encoding gene was cloned into pGAPZαA with the Saccharomyces cerevisiae α-factor signal sequence by two different ways. The two constructs consist of an additional sequence of a (His)6-tag of the vector fused to the N-terminus of this enzyme (tFSL) while the other expression vector was constructed without any additional sequence (rFSL). Compared to the native enzyme (nFSL) (18.75 mg/L), a high level secretion of rFSL (310 mg/L) and tFSL (240 mg/L) was achieved providing an important improvement in enzyme production. Biochemical characterization showed that pure recombinant proteins (rFSL and tFSL) presented similar behaviour towards triglycerides, phospholipid and galactolipid. Like the nFSL, rFSL and tFSL are active at high concentration of bile salts (4mM) and calcium ions enhanced lipase activity. During plant infection, transcripts of this fungal lipase gene were detected 3, 7 and 10 days post infection.

Renaturation and one step purification of the chicken GIIA secreted phospholipase A2 from inclusion bodies

The cDNA coding for a mature protein of 123 amino acids, containing all of the structural features of catalytically active group II sPLA2, has been amplified. The gene has been cloned into the bacterial expression vector pET-21a(+), which allows protein over-expression as inclusion bodies and enables about 3 mg per litre of pure refolded fully active enzyme to be obtained. Recombinant expression of chPLA2-IIA in Escherichia coli shows that the enzyme is Ca(2+) dependent, maximally active at pH 8-9, and hydrolyses phosphatidylglycerol versus phosphatidylcholine with a 15-fold preference. The ability to express reasonably large amounts of the sPLA2 Group IIA, compared to that obtained with the classical purification will provide a basis for future site directed mutagenesis studies of this important enzyme.

Phospholipase A2 purification and characterization: a case study

We compared here the purification procedures, the pH, the calcium, the bile salts, and the temperature dependencies as well as the catalytic activities on phosphatidylcholine (PC) and phosphatidylethanolamine (PE) of two purified secreted PLA2 from chicken pancreatic (ChPLA2-IB) and chicken intestinal (ChPLA2-IIA) origins. Interestingly, ChPLA2-IB hydrolyzes efficiently both purified PC and PE, whereas ChPLA2-IIA hydrolyzes only PE and not PC, even after a long incubation period. These analytical results clearly indicate that the catalytic activity of ChPLA2-IIA, measured with the pH-stat and using egg yolk as substrate, is mainly due to the hydrolysis of the PE fraction present in egg yolk.

Phospholipases: an overview

Phospholipids are present in all living organisms. They are a major component of all biological membranes, along with glycolipids and cholesterol. Enzymes aimed at cleaving the various bonds in phospholipids, namely phospholipases, are consequently widespread in nature, playing very diverse roles from aggression in snake venom to signal transduction, lipid mediators production, and digestion in humans. Although all phospholipases target phospholipids as substrates, they vary in the site of action on the phospholipids molecules, physiological function, mode of action, and their regulation. Significant studies on phospholipases characterization, physiological role, and industrial potential have been conducted worldwide. Some of them have been directed for biotechnological advances, such as gene discovery and functional enhancement by protein engineering. Others reported phospholipases as virulence factors and major causes of pathophysiological effects. In this introductory chapter, we provide brief details of different phospholipases.

T-cell and antibody responses to phospholipase A2 from different species show distinct cross-reactivity patterns

BACKGROUND

Secreted phospholipases A2 (sPLA2) represent antigens to which humans may be rarely or frequently exposed. Thus, the investigation of humoral and cellular immune responses to sPLA2s from different species can provide a suitable model in the study of antibody and T-cell cross-reactivity.

METHODS

Specific IgE, IgG1, IgG4, and IgA antibodies were analyzed by ELISA against sPLA2s from pancreas of Bos taurus (BT), Apis mellifera (AM) bee venom, Daboia russellii (DR) and Naja mossambica (NM) snake venoms, and human group III (hGIII) sPLA2 using sera of nonallergic beekeepers, AM-allergic patients, and healthy controls. T-cell cross-reactivity was investigated in PBMC, and T-cell clones (TCC) are generated against AM sPLA2.

RESULTS

Hyperimmune and allergic individuals showed high levels of sPLA2-specific IgG4 and significant IgG4 cross-reactivity between BT, DR, and NM sPLA2s. Furthermore, IgE, IgA, and IgG1 cross-reactivities against BT, DR, and NM sPLA2s were also detectable in the range of 22.2-44.8%. Allergic patients showed significant T-cell proliferative response to NM sPLA2 together with increased IFN-γ and IL-13 production even though they had never been exposed to cobra venom. Although nonallergic healthy controls show no cross-reactivity at T-cell level, they did have low levels of IgG4 and IgA against BT, DR, and NM sPLA2s. Human TCC spanning three major T-cell epitopes of AM sPLA2 showed minor proliferative response to NM and hGIII sPLA2s.

CONCLUSIONS

This study shows that T cells and antibodies may show cross-reactivity between different species without being naturally exposed to sPLA2s.

Immunohistochemical localization of hepatopancreatic phospholipase in gastropods mollusc, Littorina littorea and Buccinum undatum digestive cells

BACKGROUND

Among the digestive enzymes, phospholipase A2 (PLA2) hydrolyzes the essential dietary phospholipids in marine fish and shellfish. However, we know little about the organs that produce PLA2, and the ontogeny of the PLA2-cells. Accordingly, accurate localization of PLA2 in marine snails might afford a better understanding permitting the control of the quality and composition of diets and the mode of digestion of lipid food.

RESULTS

We have previously producted an antiserum reacting specifically with mSDPLA2. It labeled zymogen granules of the hepatopancreatic acinar cells and the secretory materials of certain epithelial cells in the depths of epithelial crypts in the hepatopancreas of snail. To confirm this localization a laser capture microdissection was performed targeting stained cells of hepatopancreas tissue sections. A Western blot analysis revealed a strong signal at the expected size (30 kDa), probably corresponding to the PLA2.

CONCLUSIONS

The present results support the presence of two hepatopancreatic intracellular and extracellular PLA2 in the prosobranchs gastropods molluscs, Littorina littorea and Buccinum undatum and bring insights on their localizations.

Drastic changes in the tissue-specific expression of secreted phospholipases A2 in chicken pulmonary disease

Infectious bronchitis is one of the most important diseases in poultry and it causes major economic losses. Infectious bronchitis is an acute, highly contagious, viral disease of chickens, characterized by rales, coughing, and sneezing.

Because secreted phospholipases A2 (sPLA2) are involved in inflammatory processes, the gene expressions of sPLA2s were investigated in both healthy chickens and chickens with infectious bronchitis and lung inflammation. The draft chicken genome was first scanned using human sPLA2 sequences to identify chicken sPLA2s (ChPLA2), chicken total mRNA were isolated and RT-PCR experiments were performed to amplify and then sequence orthologous cDNAs. Full-length cDNA sequences of ChPLA2-IB, -IIA, -IIE, -V and -X were cloned. The high degree of sequence identity of 50–70% between the avian and mammalian (human and mouse) sPLA2 orthologs suggests a conservation of important enzymatic functions for these phospholipases.

Quantitation by qPCR of the transcript levels of ChPLA2-IB, -IIA, -IIE, -V and -X in several tissues from healthy chicken indicated that the expression patterns and mRNA levels diverged among the phospholipases tested. In chicken with infectious bronchitis, an over expression of ChPLA2-V was observed in lungs and spleen in comparison with healthy chicken. These findings suggest that ChPLA2-V could be a potential biomarker for lung inflammation. Conversely, a down regulation of ChPLA2-IB, -IIA and -X was observed in lungs and spleen in case of infectious bronchitis. A significant increase in the expression level of ChPLA2-X and ChPLA2-IB was also noticed in pancreas. No or minor changes have been detected in the expression of ChPLA2-IIE in lungs and small intestine, but it shows a significant increase in several infected tissues.

T-cell and antibody responses to phospholipase A2 from different species show distinct cross-reactivity patterns

BACKGROUND

Secreted phospholipases A2 (sPLA2) represent antigens to which humans may be rarely or frequently exposed. Thus, the investigation of humoral and cellular immune responses to sPLA2s from different species can provide a suitable model in the study of antibody and T-cell cross-reactivity.

METHODS

Specific IgE, IgG1, IgG4, and IgA antibodies were analyzed by ELISA against sPLA2s from pancreas of Bos taurus (BT), Apis mellifera (AM) bee venom, Daboia russellii (DR) and Naja mossambica (NM) snake venoms, and human group III (hGIII) sPLA2 using sera of nonallergic beekeepers, AM-allergic patients, and healthy controls. T-cell cross-reactivity was investigated in PBMC, and T-cell clones (TCC) are generated against AM sPLA2.

RESULTS

Hyperimmune and allergic individuals showed high levels of sPLA2-specific IgG4 and significant IgG4 cross-reactivity between BT, DR, and NM sPLA2s. Furthermore, IgE, IgA, and IgG1 cross-reactivities against BT, DR, and NM sPLA2s were also detectable in the range of 22.2-44.8%. Allergic patients showed significant T-cell proliferative response to NM sPLA2 together with increased IFN-γ and IL-13 production even though they had never been exposed to cobra venom. Although nonallergic healthy controls show no cross-reactivity at T-cell level, they did have low levels of IgG4 and IgA against BT, DR, and NM sPLA2s. Human TCC spanning three major T-cell epitopes of AM sPLA2 showed minor proliferative response to NM and hGIII sPLA2s.

CONCLUSIONS

This study shows that T cells and antibodies may show cross-reactivity between different species without being naturally exposed to sPLA2s.

Immunohistochemical localization of hepatopancreatic phospholipase A2 in Hexaplex trunculus digestive cells

Background

Mammalian sPLA₂-IB localization cell are well characterized. In contrast, much less is known about aquatic primitive ones. The aquatic world contains a wide variety of living species and, hence represents a great potential for discovering new lipolytic enzymes and the mode of digestion of lipid food.

Results

The marine snail digestive phospholipase A₂ (mSDPLA₂) has been previously purified from snail hepatopancreas. The specific polyclonal antibodies were prepared and used for immunohistochimical and immunofluorescence analysis in order to determine the cellular location of mSDPLA₂. Our results showed essentially that mSDPLA₂ was detected inside in specific vesicles tentatively named (mSDPLA₂+) granules of the digestive cells. No immunolabelling was observed in secretory zymogene-like cells. This immunocytolocalization indicates that lipid digestion in the snail might occur in specific granules inside the digestive cells.

Conclusion

The cellular location of mSDPLA₂ suggests that intracellular phospholipids digestion, like other food components digestion of snail diet, occurs in these digestive cells. The hepatopancreas of H. trunculus has been pointed out as the main region for digestion, absorption and storage of lipids.

The protective effect of Malva sylvestris on rat kidney damaged by vanadium

Background

The protective effect of the common mallow (Malva sylvestris) decoction on renal damages in rats induced by ammonium metavanadate poisoning was evaluated. On the one hand, vanadium toxicity is associated to the production of reactive oxygen species, causing a lipid peroxidation and an alteration in the enzymatic antioxidant defence. On the other hand, many medicinal plants are known to possess antioxidant and radical scavenging properties, thanks to the presence of flavonoids. These properties were confirmed in Malva sylvestris by two separate methods; namely, the Diphenyl-2-picrylhydrazyl assay and the Nitroblue Tetrazolium reduction assay.

Results

In 80 rats exposed to ammonium metavanadate (0.24 mmol/kg body weight in drinking water) for 90 days, lipid peroxidation levels and superoxide dismutase, catalase and glutathione peroxidase activities were measured in kidney. A significant increase in the formation of free radicals and antioxidant enzyme activities was noticed. In addition, a histological examination of kidney revealed a structural deterioration of the renal cortical capsules and a shrinking of the Bowman space. In animals intoxicated by metavanadate but also given a Malva sylvestris decoction (0.2 g dry mallow/kg body weight), no such pathologic features were observed: lipid peroxidation levels, antioxidant enzyme activities and histological features appeared normal as compared to control rats.

Conclusion

Malva sylvestris is proved to have a high antioxidative potential thanks to its richness in phenolic compounds.

In vitro study of the PLA2 inhibition and antioxidant activities of Aloe vera leaf skin extracts

Background

In the present work we determined the total phenolic content of Aloe vera leaf skin (AVLS) extracts by using various solvents (hexane, chloroform-ethanol (1/1), ethyl acetate, butanol and water). We have also evaluated the antioxidant and the anti-PLA2 properties of these extracts by measuring their inhibition potency on the human pro-inflammatory phospholipase A2 (group IIA).

Results

The water extract exhibits the highest inhibitory effect with an IC₅₀ = 0.22 mg/ml and interestingly no effect was observed on the digestive phospholipase A2 (group IB) even at a concentration of 5 mg/ml. Antioxidant activities were also analyzed and the most active extracts were observed when using chloroform ethanol (1/1) and ethyl acetate (IC₅₀ = 0.274 and 0.326 mg/ml, respectively). Analysis of the total phenolic content reveals that the water extract, with the best anti-PLA2 effect, was poor in phenolic molecules (2 mg GAE/g). This latter value has to be compared with the chloroform-ethanol and the ethyl acetate extracts (40 and 23.8 mg GAE/g, respectively), mostly responsible for the antioxidant activity.

Conclusion

A significant correlation was established between the total phenolic content and the antioxidant capacity but not with the anti PLA2 activity. Results from phytochemical screening suggest that the anti PLA2 molecules were probably catechin tannins compounds.

Purification and biochemical characterization of a secreted group IIA chicken intestinal phospholipase A₂

Background

Secretory phospholipase A2 group IIA (IIA PLA2) is a protein shown to be highly expressed in the intestine of mammals. However, no study was reported in birds.

Results

Chicken intestinal group IIA phospholipase A₂ (ChPLA₂-IIA) was obtained after an acidic treatment (pH.3.0), precipitation by ammonium sulphate, followed by sequential column chromatographies on Sephadex G-50 and mono-S ion exchanger. The enzyme was found to be a monomeric protein with a molecular mass of around 14 kDa. The purified enzyme showed a substrate preference for phosphatidylethanolamine and phosphatidylglycerol, and didn't hydrolyse phosphatidylcholine. Under optimal assay conditions, in the presence of 10 mM NaTDC and 10 mM CaCl_2, a specific activity of 160 U.mg^-1 for purified ChPLA₂-IIA was measured using egg yolk as substrate. The fifteen NH2-terminal amino acid residues of ChPLA₂-IIA were sequenced and showed a close homology with known intestinal secreted phospholipases A₂. The gene encoding the mature ChPLA₂-IIA was cloned and sequenced. To further investigate structure-activity relationship, a 3D model of ChPLA₂-IIA was built using the human intestinal phospholipase A₂ structure as template.

Conclusion

ChPLA2-IIA was purified to homogeneity using only two chromatographic colomns. Sequence analysis of the cloned cDNA indicates that the enzyme is highly basic with a pI of 9.0 and has a high degree of homology with mammalian intestinal PLA₂-IIA.

Antibacterial properties of chicken intestinal phospholipase A2

Background

The presence of chicken group-IIA PLA2 (ChPLA2-IIA) in the intestinal secretion suggests that this enzyme plays an important role in systemic bactericidal defence. We have analyzed the bactericidal activity of purified ChPLA2-IIA, on several gram-positive and gram-negative bacteria by using the diffusion well and dilution methods.

Results

ChPLA2-IIA displays potent bactericidal activity against gram-positive bacteria but lacks bactericidal activity against gram negative ones. We have also demonstrated a synergic action of ChPLA2-IIA with lysozyme when added to the bacteria culture prior to ChPLA2-IIA. The bactericidal efficiency of ChPLA2-IIA was shown to be dependent upon the presence of calcium ions and then a correlation could be made to its hydrolytic activity of membrane phospholipids. Interestingly ChPLA2-IIA displays a higher dependence to Ca2+ ions than to Mg2+ions.

Conclusion

We conclude that the main physiological role of ChPLA2-IIA could be the defence of the intestine against bacterial invasions.

Kinetic properties of dromedary pancreatic lipase: a comparative study on emulsified and monomolecular substrate

Using the classical emulsified system and the monomolecular film technique, we compared several interfacial properties of dromedary pancreatic lipase (DrPL) with those of a mammal (human) and an avian (turkey) model. Like turkey pancreatic lipase (TPL) and unlike human pancreatic lipase (HPL), in the absence of colipase and bile salts, using tributyrin emulsion or monomolecular films of dicaprin at low surface pressure, DrPL hydrolyses pure tributyrin emulsion, as well as dicaprin films maintained at low surface pressures. DrPL was also able to hydrolyse triolein emulsion in the absence of any additive and despite the accumulation of long-chain free fatty acids at the interface. The difference of behaviours between the two mammal pancreatic lipases (DrPL and HPL) can be explained by the penetration capacity of each enzyme. DrPL presents a critical surface pressure value (21 m Nm(-1)) that is more important than this of HPL. Subsequently, the dromedary pancreatic lipase interacts efficiently with interfaces and it is not denaturated at high interfacial energy. A kinetic study on the surface pressure dependency, stereospecificity and regioselectivity of DrPL was performed using optically pure stereoisomers of either three dicaprin isomers containing a single hydrolysable decanoyl ester bond that were spread as monomolecular films at the air/water interface. Interestingly, in comparison with all the previously studied mammal pancreatic lipases, DrPL presents the highest preference for adjacent ester groups of dicaprin isomers (1,2-sn-dicaprin and 2,3-sn-dicaprin) at high surface pressure. Furthermore, DrPL forms a pancreatic lipase subgroup in which the stereopreference switches from sn-3 position to the sn-1 position when increasing the surface pressure.

Ostrich pancreatic phospholipase A2: Purification and biochemical characterization

Ostrich pancreatic phospholipase A(2) (OPLA(2)) was purified from delipidated pancreases. Pure protein was obtained after heat treatment (70 degrees C), precipitation by ammonium sulphate and ethanol, respectively followed by sequential column chromatography on MonoQ Sepharose and size exclusion HPLC column. Purified OPLA(2), which is not a glycosylated protein, was found to be monomeric protein with a molecular mass of 13773.93 Da. A specific activity of 840U/mg for purified OPLA(2) was measured at optimal conditions (pH 8.2 and 37 degrees C) in the presence of 4 mM NaTDC and 10 mM CaCl(2) using PC as substrate. This enzyme was also found to be able to hydrolyze, at low surface pressure, 1,2-dilauroyl-sn-glycero-3 phosphocholine (di C(12)-PC) monolayers. Maximal activity was measured at 5-8 mNm(-1). The sequence of the first 22 amino-acid residues at the N-terminal extremity of purified bird PLA(2) was determined by automatic Edman degradation and showed a high sequence homology with known mammal pancreatic secreted phospholipases A(2).

Recombinant production and properties of binding of the full set of mouse secreted phospholipases A2 to the mouse M-type receptor

To date, 12 secreted phospholipases A2 (sPLA2s) have been identified in the mouse species and divided into three structural collections (I/II/V/X, III, and XII). On the basis of their different molecular properties and tissue distributions, each sPLA2 is likely to exert distinct functions by acting as an enzyme or ligand for specific soluble proteins or receptors, among which the M-type receptor is the best-characterized target. Here, we present the properties of binding of the full set of mouse sPLA2s to the mouse M-type receptor. All enzymes have been produced in Escherichia coli or insect cells, and their properties of binding to the cloned and native M-type receptor have been determined. sPLA2s IB, IIA, IIE, IIF, and X are high-affinity ligands (K0.5 = 0.3-3 nM); sPLA2s IIC and V are low-affinity ligands (K0.5 = 30-75 nM), and sPLA2s IID, III, XIIA, and XIIB bind only very weakly or do not bind to the M-type receptor (K0.5 > 100 nM). Three exogenous parvoviral group XIII PLA2s and two fungal group XIV sPLA2s do not bind to the receptor. Together, these results indicate that the mouse M-type receptor is selective for only a subset of mouse sPLA2s from the group I/II/V/X structural collection. Binding of mouse sPLA2s to a recombinant soluble mouse M-type receptor leads in all cases to inhibition of enzymatic activity, and the extent of deglycosylation of the receptor decreases yet does not abolish sPLA2 binding. The physiological meaning of binding of sPLA2 to the M-type receptor is discussed on the basis of our current knowledge of sPLA2 functions.

Inhibition of Secreted Phospholipase A2. 4-Glycerol Derivatives of 4,5-Dihydro-3-(4-tetradecyloxybenzyl)-1,2,4-4H-oxadiazol-5-one with Broad Activities

Secreted phospholipases A2 (sPLA2s) have been reported to play an important role in various inflammatory conditions and thus represent an attractive therapeutic target. Previous SAR studies from our laboratory have revealed certain important features of our recently discovered specific hGIIA sPLA2 inhibitors, and we report here the synthesis and biological activities of glycerol-containing derivatives of our lead compound III (Figure 1). Efficient and selective synthesis methods have been developed to make glycerol trisubstituted by different groups on desired positions. In terms of biological activities, the best compounds (A3, A6, and A15) are more active than III (Figure 1), as potent as Me-Indoxam, an sPLA2s inhibitor of reference, against hGIIA, hGV, and hGX sPLA2s and at least 10 times less active toward the GIB enzymes in two in vitro assay systems. By synthesis of enantiopure (S)-A6, we demonstrated that no important improvement of the inhibitory potency could be achieved by this approach. Furthermore, the results show that the global lipophilicity is likely responsible for the anti-PLA2 activity and two oxadiazolone moieties seem too big to be accommodated by the active site of the hGIIA enzyme.

InSilico-Guided Target Identification of a Scaffold-Focused Library: 1,3,5-Triazepan-2,6-diones as Novel Phospholipase A2 Inhibitors

A collection of 2150 druggable active sites from the Protein Data Bank was screened by high-throughput docking to identify putative targets for five representative molecules of a combinatorial library sharing a 1,3,5-triazepan-2,6-dione scaffold. Five targets were prioritized for experimental evaluation by computing enrichment in individual protein entries among the top 2% scoring targets. Out of the five proposed proteins, secreted phospholipase A2 (sPLA2) was shown to be a true target for a panel of 1,3,5-triazepan-2,6-diones which exhibited micromolar affinities toward two human sPLA2 members.

Secreted Phospholipase A2Inhibitors Are Also Potent Blockers of Binding to the M-Type Receptor†

Mammalian secreted phospholipases A(2) (sPLA(2)s) constitute a family of structurally related enzymes that are likely to play numerous biological roles because of their phospholipid hydrolyzing activity and binding to soluble and membrane-bound proteins, including the M-type receptor. Over the past decade, a number of competitive inhibitors have been developed against the inflammatory-type human group IIA (hGIIA) sPLA(2) with the aim of specifically blocking its catalytic activity and pathophysiological functions. The fact that many of these inhibitors, including the indole analogue Me-Indoxam, inhibit several other sPLA(2)s that bind to the M-type receptor prompted us to investigate the impact of Me-Indoxam and other inhibitors on the sPLA(2)-receptor interaction. By using a Ca(2+) loop mutant derived from a venom sPLA(2) which is insensitive to hGIIA inhibitors but still binds to the M-type receptor, we demonstrate that Me-Indoxam dramatically decreases the affinity of various sPLA(2)s for the receptor, yet an sPLA(2)-Me-Indoxam-receptor complex can form at very high sPLA(2) concentrations. Me-Indoxam inhibits the binding of iodinated mouse sPLA(2)s to the mouse M-type receptor expressed on live cells but also enhances binding of sPLA(2) to phospholipids. Because Me-Indoxam and other competitive inhibitors protrude out of the sPLA(2) catalytic groove, it is likely that the inhibitors interfere with the sPLA(2)-receptor interaction by steric hindrance and to different extents that depend on the type of sPLA(2) and inhibitor. Our finding suggests that the various anti-inflammatory therapeutic effects of sPLA(2) inhibitors may be due not only to inhibition of enzymatic activity but also to modulation of binding of sPLA(2) to the M-type receptor or other as yet unknown protein targets.

Purification and biochemical characterization of phospholipase A2 from dromedary pancreas

Dromedary pancreatic PLA2 (DrPLA2) was purified from delipidated pancreases. Pure protein was obtained after heat and acidic treatment (70 degrees C; pH 3.0), precipitation by ammonium sulphate and ethanol respectively, followed by sequential column chromatographies on Sephadex G-50, MonoS Sepharose, MonoQ Sepharose and C-8 reverse phase high pressure liquid chromatography. Purified DrPLA2, which is not glycosylated protein, was found to be monomeric protein with a molecular mass of 13748.55 Da. A specific activity of 600 U/mg for purified DrPLA2 was measured at optimal conditions (pH 8.0 and 37 degrees C) in the presence of 3 mM NaTDC and 7 mM CaCl(2) using PC as substrate. The sequence of the first fourteen amino-acid residues at the N-terminal extremity of DrPLA2 was determined by automatic Edman degradation. One single sequence was obtained and shows a close similarity with all other known pancreatic secreted phospholipases A2.

Expression, purification, and characterization of His-tagged Staphylococcus xylosus lipase wild-type and its mutant Asp 290 Ala

The gene encoding the extracellular lipase of Staphylococcus xylosus (SXL) was cloned using PCR technique. The sequence corresponding to the mature lipase was subcloned in the pET-14b expression vector, with a strong T7 promoter, to construct a recombinant lipase protein containing six histidine residues at the N-terminal. High level expression of the lipase by Escherichia coli BL21 (DE3) cells harbouring the lipase gene containing expression vector was observed upon induction with 0.4 mM IPTG at 37 degrees C. One-step purification of the recombinant lipase was achieved with Ni-NTA resin. The specific activity of the purified His-tagged SXL was 1500 or 850 U/mg using tributyrin or olive oil emulsion as substrate, respectively. It has been proposed that the region near the residue Asp290 could be involved in the selection of the substrate. Therefore, we also mutated the residue Asp 290 by Ala using site-directed mutagenesis. The mutant SXL-D290A was overexpressed in E. coli BL21 (DE3) and purified with the same nickel metal affinity column. The specific activity of the purified His-tagged SXL-D290A mutant was 1000 U/mg using either tributyrin or olive oil emulsion as substrate. A comparative study of the wild type (His(6)-SXL) and the mutant (His(6)-SXL-D290A) proteins was carried out. Our results confirmed that Asp290 is important for the chain length specificity and catalytic efficiency of the enzyme.

Activation of Cytokine Production by Secreted Phospholipase A2 in Human Lung Macrophages Expressing the M-Type Receptor

Secreted phospholipases A(2) (sPLA(2)) are enzymes released in plasma and extracellular fluids during inflammatory diseases. Because human group IB and X sPLA(2)s are expressed in the lung, we examined their effects on primary human lung macrophages (HLM). Both sPLA(2)s induced TNF-alpha and IL-6 release in a concentration-dependent manner by increasing their mRNA expression. This effect was independent of their enzymatic activity because 1) the capacity of sPLA(2)s to mobilize arachidonic acid from HLM was unrelated to their ability to induce cytokine production; and 2) two catalytically inactive isoforms of group IB sPLA(2) (bromophenacyl bromide-inactivated human sPLA(2) and the H48Q mutant of the porcine sPLA(2)) were as effective as the catalytically active sPLA(2)s in inducing cytokine production. HLM expressed the M-type receptor for sPLA(2)s at both mRNA and protein levels, as determined by RT-PCR, immunoblotting, immunoprecipitation, and flow cytometry. Me-indoxam, which decreases sPLA(2) activity as well as binding to the M-type receptor, suppressed sPLA(2)-induced cytokine production. Incubation of HLM with the sPLA(2)s was associated with phosphorylation of ERK1/2, and a specific inhibitor of this pathway, PD98059, significantly reduced the production of IL-6 elicited by sPLA(2)s. In conclusion, two distinct sPLA(2)s produced in the human lung stimulate cytokine production by HLM via a mechanism that is independent of their enzymatic activity and involves activation of the ERK1/2 pathway. HLM express the M-type receptor, but its involvement in eliciting cytokine production deserves further investigation.

Secretory phospholipase A2 induces dendritic cell maturation

High level of phospholipase A(2) (PLA(2)) activity is found in serum and biological fluids during the acute-phase response (APR). Extracellular PLA(2) in fluids of patients with inflammatory diseases such as sepsis, acute pancreatitis or rheumatoid arthritis is also associated with propagation of inflammation. PLA(2) activity is involved in the release of both pro- and anti-inflammatory lipid mediators from phospholipids of cellular membranes or circulating lipoproteins. PLA(2) may thus generate signals that influence immune responses. Here, group III secretory PLA(2) were tested for their ability to promote generation of functionally mature human dendritic cells (DC). PLA(2) treatment of differentiating monocytes in the presence of granulocyte/macrophage colony-stimulating factor and IL-4 yielded cells with phenotypical and functional characteristics of mature DC. This maturation was dependent on the dose of PLA(2), and PLA(2)-generated DC stimulated IFN-gamma secretion by allogeneic T cells. The effects of PLA(2) on DC maturation was mainly dependent on enzyme activity and correlated with the activation of NF-kappaB, AP-1 and NFAT. The data suggest that transient increase in PLA(2) activity generates signals that promote transition of innate to adaptive immunity during the APR.

Cellular arachidonate-releasing function of novel classes of secretory phospholipase A2s (groups III and XII)

Here we report cellular arachidonate (AA) release and prostaglandin (PG) production by novel classes of secretory phospholipase A(2)s (sPLA(2)s), groups III and XII. Human group III sPLA(2) promoted spontaneous AA release, which was augmented by interleukin-1, in HEK293 transfectants. The central sPLA(2) domain alone was sufficient for its in vitro enzymatic activity and for cellular AA release at the plasma membrane, whereas either the unique N- or C-terminal domain was required for heparanoid-dependent action on cells to augment AA release, cyclooxygenase-2 induction, and PG production. Group III sPLA(2) was constitutively expressed in two human cell lines, in which other sPLA(2)s exhibited different stimulus inducibility. Human group XII sPLA(2) had a weak enzymatic activity in vitro and minimally affects cellular AA release and PG production. Cells transfected with group XII sPLA(2) exhibited abnormal morphology, suggesting a unique functional aspect of this enzyme. Based on the present results as well as our current analyses on the group I/II/V/X sPLA(2)s, general properties of cellular actions of a full set of mammalian sPLA(2)s in regulating AA metabolism are discussed.

Interfacial kinetic and binding properties of the complete set of human and mouse groups I, II, V, X, and XII secreted phospholipases A2

Expression of the full set of human and mouse groups I, II, V, X, and XII secreted phospholipases A(2) (sPLA(2)s) in Escherichia coli and insect cells has provided pure recombinant enzymes for detailed comparative interfacial kinetic and binding studies. The set of mammalian sPLA(2)s display dramatically different sensitivity to dithiothreitol. The specific activity for the hydrolysis of vesicles of differing phospholipid composition by these enzymes varies by up to 4 orders of magnitude, and yet all enzymes display similar catalytic site specificity toward phospholipids with different polar head groups. Discrimination between sn-2 polyunsaturated versus saturated fatty acyl chains is <6-fold. These enzymes display apparent dissociation constants for activation by calcium in the 1-225 microm range, depending on the phospholipid substrate. Analysis of the inhibition by a set of 12 active site-directed, competitive inhibitors reveals a large variation in the potency among the mammalian sPLA(2)s, with Me-Indoxam being the most generally potent sPLA(2) inhibitor. A dramatic correlation exists between the ability of the sPLA(2)s to hydrolyze phosphatidylcholine-rich vesicles efficiently in vitro and the ability to release arachidonic acid when added exogenously to mammalian cells; the group V and X sPLA(2)s are uniquely efficient in this regard.

On the Binding Preference of Human Groups IIA and X Phospholipases A2 for Membranes with Anionic Phospholipids

Mammals contain 9-10 secreted phospholipases A(2) (sPLA(2)s) that display widely different affinities for membranes, depending on the phospholipid composition. The much higher enzymatic activity of human group X sPLA(2) (hGX) compared with human group IIA sPLA(2) (hGIIA) on phosphatidylcholine (PC)-rich vesicles is due in large part to the higher affinity of the former enzyme for such vesicles; this result also holds when vesicles contain cholesterol and sphingomyelin. The inclusion of anionic phosphatidylserine in PC vesicles dramatically enhances interfacial binding and catalysis of hGIIA but not of hGX. This is the result of the large number of lysine and arginine residues scattered over the entire surface of hGIIA, which cause the enzyme to form a supramolecular aggregate with multiple vesicles. Thus, high affinity binding of hGIIA to anionic vesicles is a complex process and cannot be attributed to a few basic residues on its interfacial binding surface, as is also evident from mutagenesis studies. The main reason hGIIA binds poorly to PC-rich vesicles is that it lacks a tryptophan residue on its interfacial binding surface, a residue that contributes to the high affinity binding of hGX to PC-rich vesicles. Results show that the lag in the onset of hydrolysis of PC vesicles by hGIIA is due in part to the poor affinity of this enzyme for these vesicles. Binding affinity of hGIIA, hGX, and their mutants to PC-rich vesicles is well correlated to the ability of these enzymes to act on the PC-rich outer plasma membrane of mammalian cells.

The beta 5' loop of the pancreatic lipase C2-like domain plays a critical role in the lipase-lipid interactions

The structural similarities between the C-terminal domain of human pancreatic lipase (C-HPL) and C2 domains suggested a similar function, the interaction with lipids. The catalytic N-terminal domain (N-HPL) and C-HPL were produced as individual proteins, and their partitioning between the water phase and the triglyceride-water interface was assessed using trioctanoin emulsions (TC8). N-HPL did not bind efficiently to TC8 and was inactive. C-HPL did bind to TC8 and to a phospholipid monolayer with a critical surface pressure of penetration similar to that of HPL (15 mN m(-1)). These experiments, performed in the absence of colipase and bile salts, support an absolute requirement of C-HPL for interfacial binding of HPL. To refine our analysis, we determined the contribution to lipid interactions of a hydrophobic loop (beta 5') in C-HPL by investigating a HPL mutant in which beta 5' loop hydrophobicity was increased by introducing the homologous lipoprotein lipase (LPL) beta 5' loop. This mutant (HPL-beta 5'LPL) penetrated into phospholipid monolayers at higher surface pressures than HPL, and its level of binding to TC8 was higher than that of HPL in the presence of serum albumin (BSA), an inhibitory protein that competes with HPL for interfacial adsorption. The beta 5' loop of LPL is therefore tailored for an optimal interaction with the surface of triglyceride-rich lipoproteins (VLDL and chylomicrons) containing phospholipids and apoproteins. These observations support a major contribution of the beta 5' loop in the interaction of LPL and HPL with their respective substrates.

Exogenously added human group X secreted phospholipase A(2) but not the group IB, IIA, and V enzymes efficiently release arachidonic acid from adherent mammalian cells

Mammalian secreted phospholipases A(2) (sPLA2s) comprise a group of at least eight enzymes, including the recently identified group X sPLA2. A bacterial expression system was developed to produce human group X sPLA2 (hGX). Inhibition studies show that the sPLA2 inhibitor LY311727 binds modestly more tightly to human group IIA sPLA2 than to hGX and that a pyrazole-based inhibitor of group IIA sPLA2 is much less active against hGX. The phospholipid head group preference of vesicle-bound hGX was determined. hGX binds tightly to phosphatidylcholine vesicles, which is thought to be required to act efficiently on cells. Tryptophan 67 hGX makes a significant contribution to interfacial binding to zwitterionic vesicles. As little as 10 ng/ml hGX releases arachidonic acid for cyclooxygenase-2- dependent prostaglandin E(2) generation when added exogenously to adherent mammalian cells. In contrast, human group IIA, rat group V, and mouse group IB sPLA2s are virtually inactive at releasing arachidonate when added exogenously to adherent cells. Dislodging cells from the growth surface enhances the ability of all the sPLA2s to release fatty acids. Studies with CHO-K1 cell mutants show that binding of sPLA2s to glycosaminoglycans is not the basis for poor plasma membrane hydrolysis by group IB, IIA, and V sPLA2s.

Colipase: structure and interaction with pancreatic lipase

Colipase is a small protein cofactor needed by pancreatic lipase for the efficient dietary lipid hydrolysis. It binds to the C-terminal, non-catalytic domain of lipase, thereby stabilising an active conformation and considerably increasing the overall hydrophobic binding site. Structural studies of the complex and of colipase alone have clearly revealed the functionality of its architecture. Interestingly, a structural analogy has recently been discovered between colipase and a domain in a developmental protein (Dickkopf), based on sequence analogy and homology modeling. Whether this structural analogy implies a common function (lipid interaction) remains to be clarified. Structural analogies have also been recognised between the pancreatic lipase C-terminal domain, the N-terminal domains of lipoxygenases and the C-terminal domain of alpha-toxin. These non-catalytic domains in the latter enzymes are important for interaction with membranes. It has not been established if these domains are also involved in eventual protein cofactor binding as is the case for pancreatic lipase.

Human pancreatic lipase: colipase dependence and interfacial binding of lid domain mutants

Five key amino acid residues from human pancreatic lipase (HPL) are mutated in some pancreatic lipase-related proteins 2 (PLRP2) that are not reactivated by colipase in the presence of bile salts. One of these residues (Y403) is involved in a direct interaction between the HPL C-terminal domain and colipase. The other four residues (R256, D257, Y267, and K268) are involved in the interactions stabilizing the open conformation of the lid domain, which also interacts with colipase. Here we produced and characterized three HPL mutants: HPL Y403N, an HPL four-site mutant (R256G, D257G, Y267F, and K268E), and an HPL five-site mutant (R256G, D257G, Y267F, K268E, and Y403N), in which the HPL amino acids were replaced by those present in human PLRP2. Colipase reactivated both the HPL Y403N mutant and HPL, and Y403 is therefore not essential for lipase-colipase interactions. Both the HPL four-site and five-site mutants showed low activity on trioctanoin, were inhibited by bile salts (sodium taurodeoxycholate, NaTDC) and were not reactivated by colipase. The interfacial binding of the HPL four-site mutant to a trioctanoin emulsion was suppressed in the presence of 4 mM NaTDC and was not restored by addition of colipase. Protein blotting/protein overlay immunoassay revealed that the HPL four-site mutant-colipase interactions are not abolished, and therefore, the absence of reactivation of the HPL four-site mutant is probably due to a lid domain conformation that prevents the interfacial binding of the lipase-colipase complex. The effects of colipase were also studied with HPL(-lid), an HPL mutant showing an 18-residue deletion within the lid domain, which therefore has only one colipase interaction site. HPL(-lid) showed a low activity on trioctanoin, was inhibited by bile salts, and recovered its lipase activity in the presence of colipase. Reactivation of HPL(-lid) by colipase was associated with a strong interfacial binding of the mutant to a trioctanoin emulsion. The lid domain is therefore not essential for either the interfacial binding of HPL or the lipase-colipase interactions.

Reactivation of the totally inactive pancreatic lipase RP1 by structure-predicted point mutations

Both classical pancreatic lipase (DPL) and pancreatic lipase-related protein 1 (DPLRP1) have been found to be secreted by dog exocrine pancreas. These two proteins were purified to homogeneity from canine pancreatic juice and no significant catalytic activity was observed with dog PLRP1 on any of the substrates tested: di- and tri-glycerides, phospholipids, etc. DPLRP1 was crystallized and its structure solved by molecular replacement and refined at a resolution of 2.10 A. Its structure is similar to that of the classical PL structures in the absence of any inhibitors or micelles. The lid domain that controls the access to the active site was found to have a closed conformation. An amino-acid substitution (Ala 178 Val) in the DPLRP1 may result in a steric clash with one of the acyl chains observed in the structures of a C11 alkyl phosphonate inhibitor, a transition state analogue, bound to the classical PL. This substitution was suspected of being responsible for the absence of DPLRP1 activity. The presence of Val and Ala residues in positions 178 and 180, respectively, are characteristic of all the known PLRP1, whereas Ala and Pro residues are always present in the same positions in all the other members of the PL gene family. Introducing the double mutation Val 178 Ala and Ala 180 Pro into the human pancreatic RP1 (HPLRP1) gene yielded a well expressed and folded enzyme in insect cells. This enzyme is kinetically active on triglycerides. Our findings on DPLRP1 and HPLRP1 are therefore likely to apply to all the RP1 lipases.