Molecular characterization of murine pancreatic phospholipase A(2)

The pancreatic secretory phospholipase A(2) (sPLA(2)IB) is considered to be a digestive enzyme, although it has several important receptor-mediated functions. In this study, using the newly isolated murine sPLA(2)IB cDNA clone as a probe, we demonstrate that in addition to the pancreas, the sPLA(2)IB mRNA was expressed in extrapancreatic organs such as the liver, spleen, duodenum, colon, and lungs. We also demonstrate that sPLA(2)IB mRNA expression was detectable from the 17(th) day of gestation in the developing mouse fetus, coinciding with the time of completion of differentiation of the pancreas. Furthermore, the mRNA expression pattern of sPLA(2)IB was distinct from those of sPLA(2)IIA and cPLA(2) in various tissues examined. The murine sPLA(2)IB gene structure is well conserved, consistent with findings in other mammalian species, and this gene mapped to the region of mouse chromosome 5F1-G1.1. Taken together, our results suggest that sPLA(2)IB plays important roles both in the pancreas and in extrapancreatic tissues and that in the mouse, its expression is developmentally regulated.     

Ostrich (Struthio camelus) carboxypeptidase A: Purification,kinetic properties and characterization of the pancreatic enzyme

• 1.1. Carboxypeptidase A and carboxypeptidase A,-type from the pancreas of the ostrich were purified by water extraction of acetone powder, aminobenzylsuccinic acid affinity and hydroxylapatite chromatography.
• 2.2. The final preparations were homogeneous when subjected to SDS-PAGE and PAGE. The M, values obtained from SDS-PAGE for CPAp and CPA,-type were 34,600 and 34,400, respectively.
• 3.3. The effects of inhibitors (1,10 phenanthroline and indole-3-acetic acid), pH and temperature on CPA activity were examined. K_i-values for CPI, PPA, D-phe, D-trp and aminobenzylsuccinic acid were determined.
• 4.4. K_m, k_cat and k_cat/K_m values were determined for hipp-phe, cbz-gly-phe, cbz-(gly)₂-phe, cbz-gly-leu, cbz-(gly)₂-leu and cbz-(gly)₂-val.
• 5.5. N-terminal sequencing and amino acid analysis were performed for CPA_β and CPA_τ-type.

     

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.     

Drug-phospholipid conjugates as potential prodrugs: synthesis, characterization, and degradation by pancreatic phospholipase A(2)

The aim of the present study was the synthesis of phospholipids containing a drug molecule instead of a fatty acid. Valproic acid and ibuprofen served as model compounds. The target molecules were synthesized either starting from sn-glycero-3-phosphocholine (1) or using (S)-2-O-benzyl-1-O-tritylglycerol (11) and (R)-2-O-benzyl-1-O-tert-butyldiphenylsilylglycerol (12), respectively, as key intermediates. With respect to the surface properties and the aggregation behavior, the drug-phospholipid conjugates resembled natural phosopholipids. Upon incubation with porcine pancreatic phospholipase A(2), only compounds with a fatty acid in the sn-2 position of the glycerol backbone were degraded. Derivatives with either ibuprofen in the sn-2 position or displaying the unnatural S-configuration were resistant to enzymatic in vitro hydrolysis.     

Bacterial expression and characterization of starfish phospholipase A(2)

Phospholipase A(2) (PLA(2)) from the pyloric ceca of the starfish Asterina pectinifera showed high specific activity and characteristic substrate specificity, compared with commercially available PLA(2) from porcine pancreas. To investigate enzymatic properties of the starfish PLA(2) in further detail, we constructed a bacterial expression system for the enzyme. The starfish PLA(2) cDNA isolated previously (Kishimura et al., 2000b. cDNA cloning and sequencing of phospholipase A(2) from the pyloric ceca of the starfish Asterina pectinifera. Comp. Biochem. Physiol. 126B, 579-586) was inserted into the expression plasmid pET-16b and the PLA(2) protein was expressed in Escherichia coli BL21 (DE3) by induction with isopropyl-beta-D(-)-thiogalactopyranoside. The recombinant PLA(2) produced as inclusion bodies was dissociated with 8 M urea and 10 mM 2-mercaptoethanol and renatured by dialyzing against 10 mM Tris--HCl buffer (pH 8.0). Renatured PLA(2) was purified by subsequent column chromatographies on DEAE--cellulose (DE-52) and Sephadex G-50. Although an N-terminal Ser in the native starfish PLA(2) was replaced by an Ala in the recombinant PLA(2), the recombinant enzyme showed essentially the same properties as did the native PLA(2) with respect to specific activity, substrate specificity, optimum pH and temperature, and Ca(2+) requirement.     

The expanding superfamily of phospholipase A(2) enzymes: classification and characterization

The phospholipase A(2) (PLA(2)) superfamily consists of a broad range of enzymes defined by their ability to catalyze the hydrolysis of the middle (sn-2) ester bond of substrate phospholipids. The hydrolysis products of this reaction, free fatty acid and lysophospholipid, have many important downstream roles, and are derived from the activity of a diverse and growing superfamily of PLA(2) enzymes. This review updates the classification of the various PLA(2)'s now described in the literature. Four criteria have been employed to classify these proteins into one of the 11 Groups (I-XI) of PLA(2)'s. First, the enzyme must catalyze the hydrolysis of the sn-2 ester bond of a natural phospholipid substrate, such as long fatty acid chain phospholipids, platelet activating factor, or short fatty acid chain oxidized phospholipids. Second, the complete amino acid sequence of the mature protein must be known. Third, each PLA(2) Group should include all of those enzymes that have readily identifiable sequence homology. If more than one homologous PLA(2) gene exists within a species, then each paralog should be assigned a Subgroup letter, as in the case of Groups IVA, IVB, and IVC PLA(2). Homologs from different species should be classified within the same Subgroup wherever such assignments are possible as is the case with zebra fish and human Group IVA PLA(2) orthologs. The current classification scheme does allow for historical exceptions of the highly homologous Groups I, II, V, and X PLA(2)'s. Fourth, catalytically active splice variants of the same gene are classified as the same Group and Subgroup, but distinguished using Arabic numbers, such as for Group VIA-1 PLA(2) and VIA-2 PLA(2)'s. These four criteria have led to the expansion or realignment of Groups VI, VII and VIII, as well as the addition of Group XI PLA(2) from plants.     

Partial purification and characterization of phosphatidic acid-specific phospholipase A(1) in porcine platelet membranes

We have shown previously that the phospholipase A (PLA) activity specific for phosphatidic acid (PA) in porcine platelet membranes is of the A(1) type (PA-PLA(1)) [J. Biol. Chem. 259 (1984) 5083]. In the present study, the PA-PLA(1) was solubilized in Triton X-100 from membranes pre-treated with 1 M NaCl, and purified 280-fold from platelet homogenates by sequential chromatography on blue-Toyopearl, red-Toyopearl, DEAE-Toyopearl, green-agarose, brown-agarose, polylysine-agarose, palmitoyl-CoA-agarose and blue-5PW columns. In the presence of 0.1% Triton X-100 in the assay mixture, the partially purified enzyme hydrolyzed the acyl group from the sn-1 position of PA independently of Ca(2+) and was highly specific for PA; phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), and phosphatidylinositol (PI) were poor substrates. The enzyme exhibited lysophospholipase activity for l-acyl-lysoPA at 7% of the activity for PA hydrolysis but no lipase activity was observed for triacylglycerol (TG) and diacylglycerol (DG). At 0.025% Triton X-100, the enzyme exhibited the highest activity, and PA was the best substrate, but PE was also hydrolyzed substantially. The partially purified PA-PLA(1) in porcine platelet membranes was shown to be different from previously purified and cloned phospholipases and lipases by comparing the sensitivities to a reducing agent, a serine-esterase inhibitor, a PLA(2) inhibitor, a Ca(2+)-independent phospholipase A(2) inhibitor, and a DG lipase inhibitor.     

Partial purification and kinetic characterization of the microsomal phospholipase A2 from thermally acclimated rainbow trout (Salmo garidneri)

Summary Phospholipase A₂ (PLA₂) was extracted from liver microsomal membranes of both 5 and 20°C-acclimated rainbow trout (Salmo gairdneri), using the non-ionic detergent, Triton X-100. Further purification was achieved by precipitation with 35–65% ammonium sulfate followed by gel filtration chromatography in the presence of 0.1% Triton X-100 on Sephadex G-200. These procedures resulted in a 30-fold purification and the removal of all traces of phospholipid from the enzyme of both warm-and cold-acclimated trout. Column elution profiles were similar for both acclimation groups, yielding a molecular weight estimate for the trout liver enzyme of 73,000. Comparisons of activity levels and kinetic parameters of PLA₂ from warm-and cold-acclimated fish, indicated that compensation for temperature at nonsaturating substrate concentrations was an attribute of both the particulate (microsomal) enzyme and the lipid-free protein. Cold acclimation resulted in higher activity belowV _max due primarily to decreased apparentK _m values. These adaptations to temperature could not be attributed to the interaction of the enzyme with the membrane lipids, but were due to qualitative changes in the enzyme that resulted from acclimation. Other adaptive qualities of PLA₂, such as reducedK _m in response to acute decreases in temperature in warm-acclimated fish, were only apparent in particulate preparations, and thus were a function of the protein-lipid complex. These data suggest that an acclimation-induced increase in the activity of PLA₂ may result in the activation of a deacylation-reacylation cycle at cold temperatures.Abbreviations PAGE polyacrylamide gel electrophoresis - PC phosphatidylcholine - PLA ₂ phospholipase A₂ - SDS sodium dodecylsulfate     

Identification and functional characterization of adipose-specific phospholipase A2 (AdPLA)

Phospholipases A(2) (PLA(2)s) catalyze hydrolysis of fatty acids from the sn-2 position of phospholipids. Here we report the identification and characterization of a membrane-associated intracellular calcium-dependent, adipose-specific PLA(2) that we named AdPLA (adipose-specific phospholipase A(2)). We found that AdPLA was highly expressed specifically in white adipose tissue and was induced during preadipocyte differentiation into adipocytes. Clearance of AdPLA by immunoprecipitation significantly decreased PLA activity in white adipose tissue lysates but had no effect on liver lysates, where expression was hardly detectable. In characterizing AdPLA, we employed radiochemical assays with TLC analysis of the enzyme activity of lysates from COS-7 cells overexpressing AdPLA. For kinetic studies, we produced purified recombinant AdPLA for use in a lipoxidase-coupled spectrophotometric assay. AdPLA generated free fatty acid and lysophospholipid from phosphatidylcholine with a preference for hydrolysis at the sn-2 position. Although we found low but detectable lysophospholipase activity, AdPLA showed no significant activity against a variety of other lipid substrates. Calcium was found to activate AdPLA but was not essential for activity. Studies with known phospholipase inhibitors, including bromoenolactone, methyl arachidonyl fluorophosphate, AACOCF(3), 7,7-dimethyl-5,8-eicosadienoic acid, and thioetheramide, supported that AdPLA is a phospholipase. Mutational studies showed that His-23 and Cys-113 are critical for activity of AdPLA and suggested that AdPLA is likely a His/Cys PLA(2). Overall, although AdPLA is similar to other histidine phospholipases in pH and calcium dependence, AdPLA showed different characteristics in many regards, including predicted catalytic mechanism. AdPLA may therefore represent the first member of a new group of PLA(2)s, group XVI.     

A novel inositol-phospholipid-specific phospholipase C. Rapid purification and characterization

A novel bovine brain inositol-phospholipid-specific phospholipase C has been identified on the basis of chromatographic behaviour and purified to apparent homogeneity by a rapid three-step procedure. The purified enzyme has a molecular mass of 85 kDa on SDS/polyacrylamide gel electrophoresis and a specific activity of 24 mumol.min-1.mg-1. The enzyme is dependent on Ca2+ and shows a marked preference for inositol phospholipid substrates. The unique nature of this polypeptide was confirmed through partial protein sequence analysis.     

Cytosolic phospholipase A2: biochemical properties and physiological roles

Phosphatidylcholine (PC) is a major constituent of biological membranes and a component of serum lipoproteins and pulmonary surfactants. The PC and other glycerophospholipid compositions of membranes change dynamically through stimulus-dependent and independent pathways, principally by the action of two different types of enzymes; phospholipase A2 [EC 3.1.1.4] and acyl-CoA:lysophospholipid acyltransferase [EC 2.3.1.23]. Phospholipase A2 is a key enzyme that catalyzes deacylation of the sn-2 position of glycerophospholipids. This enzyme is critical in the remodeling of membrane lipids and formation of two subclasses of lipid mediators, fatty acid derivatives and lysophospholipids. Among many different subtypes of phospholipase A2 enzymes, we found that cytosolic phospholipase A2alpha (cPLA2alpha) is important in various pathological and physiological responses. Here, we summarize the phenotypes resulting from genetic ablation of cPLA2alpha, and the properties of newly discovered enzymes in the cPLA2 family. Comprehensive analysis of lipid mediators using liquid chromatography-tandem mass spectrometry (LC-MS/MS) is useful for understanding the roles of individual mediators in physiological and pathological processes.     

Adsorption of pancreatic (pro)phospholipase A2 to various physiological substrates

The adsorption of pancreatic phospholipase was studied in vitro in the presence of egg yolk lipoprotein emulsion, Intralipid emulsion, and milk fat globules. When the emulsions are incubated with bile salts, the latter dissociate a considerable fraction of the phospholipids initially associated with the emulsions, leading to the coexistence of an emulsified phase and a phase of mixed micelles. After the addition of pancreatic phospholipase A2, gel filtration shows that the enzyme was more than 90% bound to mixed micelles, regardless of the type of emulsion used. Comparable results were obtained by replacing the bile salts with human gallbladder bile. In parallel, pancreatic zymogen was never found to be bound to any of the lipid structures present (emulsion or mixed micelles). When the catalytic site of pancreatic phospholipase A2 was blocked with 4-bromophenacylbromide, there was no fixation on mixed micelles. Fixation was restored by the presence of lysolecithins and fatty acids in the incubation mixtures. The partial transformation of all emulsified substrates to mixed micelles by bile salts in vivo would thus lead to optimum activity of pancreatic phospholipase A2.     

Glucose kinase of Streptomyces coelicolor A3(2): large-scale purification and biochemical analysis

Glucose kinase of Streptomyces coelicolor A3(2) is essential for glucose utilisation and is required for carbon catabolite repression (CCR) exerted through glucose and other carbon sources. The protein belongs to the ROK-family, which comprises bacterial sugar kinases and regulators. To better understand glucose kinase function, we have monitored the cellular activity and demonstrated that the choice of carbon sources did not significantly change the synthesis and activity of the enzyme. The DNA sequence of the Streptomyces lividans glucose kinase gene glkA was determined. The predicted gene product of 317 amino acids was found to be identical to S. coelicolor glucose kinase, suggesting a similar role for this protein in both organisms. A procedure was developed to produce pure histidine-tagged glucose kinase with a yield of approximately 10 mg/l culture. The protein was stable for several weeks and was used to raise polyclonal antibodies. Purified glucose kinase was used to explore protein-protein interaction by surface plasmon resonance. The experiments revealed the existence of a binding activity present in S. coelicolor cell extracts. This indicated that glucose kinase may interact with (an)other factor(s), most likely of protein nature. A possible cross-talk with proteins of the phosphotransferase system, which are involved in carbon catabolite repression in other bacteria, was investigated.     

Recombinant human glucagon: Large-scale purification and biochemical characterization

Recombinant glucagon was expressed inEscherichia coli as a fusion protein including the glucagon sequence therein as previously reported [Ishizakiet al. (1992).Appl. Microbiol. Biotechnol.36, 483–486]. We developed a large-scale method for the isolation and purification of recombinant glucagon. After cell disruption, the resultant pellets were solubilized with 2 M guanidine-HCl, to whichStaphylococcus aureus V8 protease had been added, and were digested into intermediates composed of 53- and 60-residue peptides containing the glucagon moiety. After the digestion came to an end, the solution was desalted, and the remaining V8 protease was allowed to resume digestion of the intermediates into glucagon, followed by partial purification by S-Sepharose and Sephacryl S-100 chromatographies. The glucagon obtained was found to be not less than 99.5% pure by analytical HPLC. One liter of culture produced about 180 mg of pure glucagon. The amino acid composition and the sequence agreed well with the theoretical values. Radioreceptor assay gave an affinity constant similar to that of pancreatic glucagon, and similar activities in cAMP production and glycogenolysis were also observed. Thus, the recombinant glucagon was confirmed to be biochemically identical with pancreatic glucagon.     

Purification of turkey pancreatic phospholipase A2

Turkey pancreatic phospholipase (TPP) has been purified from delipidated pancreases. The purification included ammonium sulfate fractionation, acidic (pH 5) treatment, followed by sequencial column chromatographies on DEAE-cellulose, Sephadex G-75, and reverse phase high pressure liquid chromatography. The purified enzyme was found to be a monomeric protein with molecular mass of 14 kDa. The optimal activity was measured at pH 8 and 37 degrees C using egg yolk emulsion as substrate. Our results show that the enzyme (TPP) was not stable for 1 h at 60 degrees C, and that bile salt and Ca2+ were required for the expression of the purified enzyme. The sequence of the N-terminal amino acids of the purified enzyme shows a very close similarity between TPP and all other known pancreatic phospholipases.     

Calcium-independent phospholipase A(2): structure and function

The classical Ca(2+)-independent phospholipase A(2) enzyme, now known as Group VIA PLA(2), was initially purified and characterized from the P388D(1) macrophage-like cell line. The corresponding cDNA was subsequently cloned from a variety of sources, and it is now known that multiple splice variants of the enzyme are expressed, some of which may act as negative regulators of the active enzyme. Group VIA PLA(2) has a consensus lipase motif (GTSTG) containing the catalytic serine, is 85-88 kDa, and exists in an aggregated form. The enzyme contains multiple ankyrin repeats, which may play a role in oligomerization. The Group VIA enzyme exhibits lysophospholipase activity as well as phospholipase A(2) activity, and it is capable of hydrolyzing a wide variety of phospholipid substrates. A major function of Group VIA PLA(2) is to mediate phospholipid remodeling, but the enzyme may play other roles as well. Other Ca(2+)-independent PLA(2) enzymes have more recently been identified, and it may be possible to discriminate between the various Ca(2+)-independent PLA(2) enzymes based on sequence or inhibitor-sensitivity. However, the physiological functions of the newly identified enzymes have yet to be elucidated.