Biochemical properties of cloned lipases from the Pseudomonas family

Structure elucidation of Staphylococcus capitis lipase. Molecular dynamics simulations to investigate the effects of calcium and zinc ions on the structural stability

Cold-adapted and organic solvent tolerant lipases have significant potential in a wide range of synthetic reactions in industry. But there are no sufficient studies on how these enzymes interacts with their substrates. Herein, the predicted structure and function of the Staphylococcus capitis lipase (SCL) are studied. Given the high amino acid sequence homology with the Staphylococcus simulans lipase (SSL), 3D structure models of closed and open forms of the S. capitis lipase were built using the structure of SSL as template. The models suggested the presence of a main lid and a second lid that may act with the former as a double door to control the access to the active site. The SCL models also allowed us to identify key residues involved in binding substrates, calcium or zinc ions. By following this model and utilizing molecular dynamics (MD) simulations, the stability of the S. capitis lipase at low temperatures could be explained in the presence and in the absence of calcium and zinc. Due to its thermolability, the SCL is extremely valuable for different biotechnological applications in a wide variety of industries from molecular biology to detergency to food and beverage preparation.Communicated by Ramaswamy H. Sarma.

Purification and characterization of a phospholipid-hydrolyzing phosphoesterase produced by Pediococcus acidilactici isolated from Gouda cheese

Lipolysis occurs during ripening of dairy products as a result of esterase or lipase activity. Lactic acid bacteria (LAB) are considered to be weakly lipolytic bacteria compared with other species. In cheeses with extended ripening periods, lipolytic LAB may have several advantages. Pediococcus acidilactici is a LAB frequently found in fermented dairy products, but no previous reports exist on their production of esterases or lipases. Our interest in the relationship of LAB and enzymatic characterization is due to the multiple reports of the benefits of LAB in the gut microbiome, particularly at the intestinal membrane. Pediococci have been characterized as probiotic and especially active in membrane interactions. The aim of this project was to purify, characterize, and identify the phosphoesterase produced by P. acidilactici originally isolated from Gouda cheese and determine its phospholipid (PL) hydrolysis profile, with a focus on increased absorption of these compounds in the human gut. Native zymograms were performed to identify a protein with lipolytic activity in the intracellular fraction of P. acidilactici. The enzyme was purified via size-exclusion HPLC, concentrated via ultrafiltration, and identified using sequence analysis in liquid chromatography (LC)-MS/MS. The purified fraction was subjected to biochemical characterization as a function of pH, temperature, ion concentration, hydrolysis of different substrates, and PL. A single protein with a molecular weight of 86 kDa and esterase activity was detected by zymography. Analysis of the LC-MS/MS results identified a putative metallophosphoesterase with a calculated molecular weight of 45.5 kDa, suggesting that this protein is active as a homodimer. The pure protein showed an optimal activity between pH 8.0 to 9.0. The optimal temperature for activity was 37°C, and the enzyme lost 15% of activity after incubation at 90°C for 1 h. This enzyme showed activity on short-chain fatty acids and exhibited high hydrolysis of phosphatidylinositol. It also hydrolyzed phosphatidylserine, phosphatidylcholine, and sphingomyelin. Phosphatidylethanolamine was hydrolyzed but with less efficiency. The characteristics and lipolytic actions exerted by this protein obtained from LAB hold promise for a potential strain of esterase or lipase that may exert human health benefits through increased digestibility and absorption of nutrients found in dairy products.

Extracellular lipase from Pseudomonas aeruginosa JCM5962(T): Isolation, identification, and characterization

The study was done to isolate, identify, and characterize a good lipolytic strain from soil. Lipolytic strain isolation was done using tributyrin agar medium. The biochemical testing and 16S rRNA gene sequencing analysis was done for identification. The enzyme was purified using ammonium sulfate precipitation and column chromatography. Results have shown a novel high lipolytic strain of P. aeruginosa JCM5962(T), isolated from soil of sugarcane field. The 16S rRNA sequence analysis confirmed the strain as P. aeruginosa JCM5962(T); further, the sequence was submitted to Genbank (KX946966.1). The isolate produced an extracellular lipase which was purified as single band of 31 kDa. Maximum lipase activity was observed at 50 °C and pH 8.0. Activity was enhanced in the presence of cobalt and benzene solvent, whereas mercury, sodium dodecyl sulfate, and chloroform inhibited it. The enzyme's marked stability and activity at high temperature, alkaline pH and organic solvents suggest that this can be effectively used in a variety of applications in industries and as biotechnological tools.

Classification of lipolytic enzymes and their biotechnological applications in the pulping industry

In the pulp and paper industry, during the manufacturing process, the agglomeration of pitch particles (composed of triglycerides, fatty acids, and esters) leads to the formation of black pitch deposits in the pulp and on machinery, which impacts on the process and pulp quality. Traditional methods of pitch prevention and treatment are no longer feasible due to environmental impact and cost. Consequently, there is a need for more efficient and environmentally friendly approaches. The application of lipolytic enzymes, such as lipases and esterases, could be the sustainable solution to this problem. Therefore, an understanding of their structure, mechanism, and sources are essential. In this report, we review the microbial sources for the different groups of lipolytic enzymes, the differences between lipases and esterases, and their potential applications in the pulping industry.

Fungal genomes mining to discover novel sterol esterases and lipases as catalysts

BACKGROUND

Sterol esterases and lipases are enzymes able to efficiently catalyze synthesis and hydrolysis reactions of both sterol esters and triglycerides and due to their versatility could be widely used in different industrial applications. Lipases with this ability have been reported in the yeast Candida rugosa that secretes several extracellular enzymes with a high level of sequence identity, although different substrate specificity. This versatility has also been found in the sterol esterases from the ascomycetes Ophiostoma piceae and Melanocarpus albomyces.

RESULTS

In this work we present an in silico search of new sterol esterase and lipase sequences from the genomes of environmental fungi. The strategy followed included identification and search of conserved domains from these versatile enzymes, phylogenetic studies, sequence analysis and 3D modeling of the selected candidates.

CONCLUSIONS

Six potential putative enzymes were selected and their kinetic properties and substrate selectivity are discussed on the basis of their similarity with previously characterized sterol esterases/lipases with known structures.

Structure of the alkalohyperthermophilic Archaeoglobus fulgidus lipase contains a unique C-terminal domain essential for long-chain substrate binding

Several crystal structures of AFL, a novel lipase from the archaeon Archaeoglobus fulgidus, complexed with various ligands, have been determined at about 1.8 A resolution. This enzyme has optimal activity in the temperature range of 70-90 degrees C and pH 10-11. AFL consists of an N-terminal alpha/beta-hydrolase fold domain, a small lid domain, and a C-terminal beta-barrel domain. The N-terminal catalytic domain consists of a 6-stranded beta-sheet flanked by seven alpha-helices, four on one side and three on the other side. The C-terminal lipid binding domain consists of a beta-sheet of 14 strands and a substrate covering motif on top of the highly hydrophobic substrate binding site. The catalytic triad residues (Ser136, Asp163, and His210) and the residues forming the oxyanion hole (Leu31 and Met137) are in positions similar to those of other lipases. Long-chain lipid is located across the two domains in the AFL-substrate complex. Structural comparison of the catalytic domain of AFL with a homologous lipase from Bacillus subtilis reveals an opposite substrate binding orientation in the two enzymes. AFL has a higher preference toward long-chain substrates whose binding site is provided by a hydrophobic tunnel in the C-terminal domain. The unusually large interacting surface area between the two domains may contribute to thermostability of the enzyme. Two amino acids, Asp61 and Lys101, are identified as hinge residues regulating movement of the lid domain. The hydrogen-bonding pattern associated with these two residues is pH dependent, which may account for the optimal enzyme activity at high pH. Further engineering of this novel lipase with high temperature and alkaline stability will find its use in industrial applications.

Purification and characterization of an alkaline lipase from Pseudomonas aeruginosa isolated from putrid mineral cutting oil as component of metalworking fluid

Extracellular lipase was isolated and purified from the culture broth of Pseudomonas aeruginosa, an extremophile which naturally grows in water-soluble mineral cutting oil (pH 10) used as metalworking fluid (MWF) for cooling and lubrication in industrial metalworking processes. The molecular mass of the purified lipase was estimated by SDS-PAGE to be 54 kDa. The optimum pH and temperature were 11 and 70 degrees C, respectively. The enzyme is stabile over a broad pH range (pH 4-11.5). The lipase preferably acted on triacylglycerols with medium-chain fatty acids. The lipase was inhibited strongly by Zn(2+), Hg(2+), Cu(2+) and slightly by Ca(2+) and Mg(2+). Non-ionic detergents and sodiumdeoxycholate enhanced lipase activity. Alkaline lipase from P. aeruginosa, capable of growing in a water-restricted medium has excellent properties and good potential for biotechnological applications in the metal industry. Its marked stability and activity in organic solvents suggest that this lipase is highly suitable as a biotechnological tool in a water-restricted medium with a variety of applications including organosynthetic reactions and the control and prevention of MWF putrification in the metal industry.

Novel family of cholesterol esterases produced by actinomycetes bacteria

Although cholesterol esterase (CHE; EC 3.1.1.13) is widespread in nature, CHEs from Streptomyces lavendulae and Streptomyces sp. X9 are the only known CHEs produced by actinomycetes. We purified CHEs from S. avermitilis JCM5070, and S. griseus IFO13350 and identified four new CHEs from actinomycetes. The enzymic properties of the CHEs from Streptomyces sp. X9, S. avermitilis, and S. griseus including substrate specificity, sensitivity to inhibitors and optimal conditions for catalysis were similar. We identified genes for the CHEs from Streptomyces sp. X9 and S. avermitilis and the encoded predicted sequences comprised 217 and 214 amino acid residues, respectively, with 64% similarity. The CHEs from Streptomyces sp. X9 and S. avermitilis were also 54 and 57% similar, respectively, to S. lavendulae CHE, indicating that these CHEs are orthologs. Phylogenetic analysis showed that they are distantly related to the conventional lipase/esterase type CHEs from mammals, yeasts and other bacteria. The actinomycetes CHEs did not have the Gly-Xaa-Ser-Xaa-Gly sequence that is conserved in the lipase/esterase family. A database search showed that orthologs of this type of CHE were restricted to actinomycetes. These findings imply that the actinomycetes CHEs constitute a novel family of cholesterol esterases.

Characterization of Melanocarpus albomyces steryl esterase produced in Trichoderma reesei and modification of fibre products with the enzyme

Melanocarpus albomyces steryl esterase STE1 is considered to be an interesting tool for several industrial applications due to its broad substrate specificity. STE1 was produced in the filamentous fungus Trichoderma reesei in a laboratory bioreactor at an estimated production level of 280 mg l(-l). The properties of the purified recombinant enzyme (rSTE1), such as substrate specificity, molecular mass, pH optimum and stability and thermostability, were characterized and compared to the corresponding properties of the native enzyme. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed one band with a molecular weight of 60 kDa for rSTE1, whereas analytical gel filtration showed a dimeric structure with a molecular weight of 120 kDa. The rSTE1 was somewhat less stable under different conditions and had slightly lower activities on various substrates than the native STE1. The effects of rSTE1 on the properties of paper sheets and polyethylene terephthalate (PET) fabric were preliminarily evaluated. Due to the hydrolysis of triglycerides and steryl esters by the rSTE1 treatment, the tensile strength and hydrophilicity of the paper were increased. The rSTE1 treatment increased significantly the polarity of PET by hydrolysing the ester bonds in the polyester backbone. Dyeing of PET with methylene blue was also slightly improved after rSTE1 treatment.

Purification, characterization, and molecular cloning of organic-solvent-tolerant cholesterol esterase from cyclohexane-tolerant Burkholderia cepacia strain ST-200

Extracellular cholesterol esterase of Burkholderia cepacia strain ST-200 was purified from the culture supernatant. Its molecular mass was 37 kDa. The enzyme was stable at pH 5.5-12 and active at pH 5.5-6, showing optimal activity at pH 7.0 at 45 degrees C. Relative to the commercially available cholesterol esterases, the purified enzyme was highly stable in the presence of various water-miscible organic solvents. The enzyme preferentially hydrolyzed long-chain fatty acid esters of cholesterol, except for that of cholesteryl palmitate. The enzyme exhibited lipolytic activity toward various p-nitrophenyl esters. The hydrolysis rate of p-nitrophenyl caprylate was enhanced 3.5- to 7.2-fold in the presence of 5-20% (vol/vol) water-miscible organic solvents relative to that in the absence of organic solvents. The structural gene encoding the cholesterol esterase was cloned and sequenced. The primary translation product was predicted to be 365 amino acid residues. The mature product is composed of 325 amino acid residues. The amino acid sequence of the product showed the highest similarity to the lipase LipA (87%) from B. cepacia DSM3959.

Novel cholesterol esterase secreted by Streptomyces persists during aqueous long-term storage

We isolated a moderate thermophilic actinomycete, Streptomyces sp. X9, from soil and purified cholesterol esterase (CHE) from the culture medium to homogeneity. The molecular masses of the purified CHE estimated by sodium dodecyl sulfate polyacrylamide gel electrophoresis and gel filtration chromatography were 23.6 and 163 kDa, respectively, indicating that the enzyme assumes an oligomeric form. Heavy metals such as Hg2+ and Ag+ similarly inhibited the activity of the CHE in the same manner as those of other bacterial CHEs. The activity of Streptomyces sp. X9 CHE was susceptible to dithiothreitol, beta-mercaptoethanol and p-chloromercuribenzoate, but resistant to phenylmethylsulfonyl fluoride, unlike those of other bacterial CHEs. The purified CHE could utilize both cholesteryl and p-nitrophenyl (pNP) esters of fatty acids as substrates. Steady-state kinetics revealed respective Km values for cholesteryl myristate and pNP-myristate of 0.34 and 1.1 mM, indicating that the cholesteryl residue is important for catalysis. We also found that the Km for the pNP esters are dependent on the chain length of the substrate fatty acid residues. These results indicate that the novel CHE specifically hydrolyzes substrates by recognizing both cholesteryl and fatty acid moieties. The enzyme was stable during long-term aqueous storage at room temperature, indicating its potential application as a diagnostic reagent.

Continuous monitoring of cholesterol oleate hydrolysis by hormone-sensitive lipase and other cholesterol esterases

Hormone-sensitive lipase (HSL) contributes importantly to the hydrolysis of cholesteryl ester in steroidogenic tissues, releasing the cholesterol required for adrenal steroidogenesis. HSL has broad substrate specificity, because it hydrolyzes triacylglycerols (TAGs), diacylglycerols, monoacylglycerols, and cholesteryl esters. In this study, we developed a specific cholesterol esterase assay using cholesterol oleate (CO) dispersed in phosphatidylcholine and gum arabic by sonication. To continuously monitor the hydrolysis of CO by HSL, we used the pH-stat technique. For the sake of comparison, the hydrolysis of CO dispersion was also tested using other cholesteryl ester-hydrolyzing enzymes. The specific activities measured on CO were found to be 18, 100, 27, and 3 micromol/min/mg for HSL, cholesterol esterase from Pseudomonas species, Candida rugosa lipase-3, and cholesterol esterase from bovine pancreas, respectively. The activity of HSL on CO is approximately 4- to 5-fold higher than on long-chain TAGs. In contrast, with all other enzymes tested, the rates of TAG hydrolysis were higher than those of CO hydrolysis. The relatively higher turnover of HSL on CO observed in vitro adds further molecular insight on the physiological importance of HSL in cholesteryl ester catabolism in vivo. Thus, HSL could be considered more as a cholesteryl ester hydrolase than as a TAG lipase.

Acinetobacter lipases: molecular biology, biochemical properties and biotechnological potential

Lipases (EC 3.1.1.3) have received increased attention recently, evidenced by the increasing amount of information about lipases in the current literature. The renewed interest in this enzyme class is due primarily to investigations of their role in pathogenesis and their increasing use in biotechnological applications. Also, many microbial lipases are available as commercial products, the majority of which are used in detergents, cosmetic production, food flavoring, and organic synthesis. Lipases are valued biocatalysts because they act under mild conditions, are highly stable in organic solvents, show broad substrate specificity, and usually show high regio- and/or stereo-selectivity in catalysis. A number of lipolytic strains of Acinetobacter have been isolated from a variety of sources and their lipases possess many biochemical properties similar to those that have been developed for biotechnological applications. This review discusses the biology of lipase expression in Acinetobacter, with emphasis on those aspects relevant to potential biotechnology applications.

Outbreak of Burkholderia cepacia bacteremia traced to contaminated hospital water used for dilution of an alcohol skin antiseptic

OBJECTIVE

To identify the source of an epidemic of Burkholderia cepacia bloodstream infections during 7 years (411 episodes in 361 patients).

DESIGN

Outbreak investigation.

SETTING

A 250-bed university hospital in Beirut, Lebanon.

METHODS

Matched case-control and retrospective cohort studies, and microbiological surveillance and polymerase chain reaction-restriction fragment length ascertainment were employed. Special media and filtration techniques were used to isolate organisms from water and diluted alcohol solutions.

RESULTS

In a group of 50 randomly selected case-matched patients from 1999, the positive blood cultures were concomitant with fever in 98%, intravenous phlebitis in 44%, and recurrent bacteremia in 20%. Fever disappeared approximately 6 hours after intravenous catheter removal. Polymerase chain reaction-restriction fragment length polymorphism revealed strain homogeneity in patient, water, and alcohol isolates. Contaminated tap water had been used to dilute alcohol for skin antisepsis and for decontamination of the caps of heparin vials. Only sporadic cases directly attributable to breach of protocol were reported after single-use alcohol swabs were substituted.

CONCLUSION

This is potentially the largest single-source nosocomial bloodstream infection outbreak ever reported, and the first report of an alcohol skin antiseptic contaminated by tap water as a source for nosocomial bacteremia.

Purification and characterization of an alkaline lipase from a newly isolated Pseudomonas mendocina PK-12CS and chemoselective hydrolysis of fatty acid ester

Lipase isolated from a soil isolate, Pseudomonas mendocina (PK-12CS) chemoselectively hydrolyzed the fatty ester group in presence of arbamate of compound 5-amino-2,4-dihydro-3H-1,2,4-triazole-3 ones, a class of compounds which are attractive starting materials for the synthesis of triazole annealed heterocycles. The enzymatic method provides an easy access to the synthesis of N-substituted glycine. Under optimized fermentation conditions the culture produced 3510 Lipolytic Units/mL of cell free fermentation broth in 20 h of fermentation. The purified lipase exhibited molecular mass of 80 kDa on SDS polyacrylamide gel electrophoresis. The enzyme was stable at room temperature for more than a month and expressed maximum activity at 37 degrees C and pH 8.

A new type of thermoalkalophilic hydrolase of Paucimonas lemoignei with high specificity for amorphous polyesters of short chain-length hydroxyalkanoic acids

A novel type of hydrolase was purified from culture fluid of Paucimonas (formerly Pseudomonas) lemoignei. Biochemical characterization revealed an unusual substrate specificity of the purified enzyme for amorphous poly((R)-3-hydroxyalkanoates) (PHA) such as native granules of natural poly((R)-3-hydroxybutyrate) (PHB) or poly((R)-3-hydroxyvalerate) (PHV), artificial cholate-coated granules of natural PHB or PHV, atactic poly((R,S)-3-hydroxybutyrate), and oligomers of (R)-3-hydroxybutyrate (3HB) with six or more 3HB units. The enzyme has the unique property to recognize the physical state of the polymeric substrate by discrimination between amorphous PHA (good substrate) and denatured, partially crystalline PHA (no substrate). The pentamers of 3HB or 3HV were identified as the main products of enzymatic hydrolysis of native PHB or PHV, respectively. No activity was found with any denatured PHA, oligomers of (R)-3HB with five or less 3HB units, poly(6-hydroxyhexanoate), substrates of lipases such as tributyrin or triolein, substrates for amidases/nitrilases, DNA, RNA, casein, N-alpha-benzoyl-l-arginine-4-nitranilide, or starch. The purified enzyme (M(r) 36,209) was remarkably stable and active at high temperature (60 degrees C), high pH (up to 12.0), low ionic strength (distilled water), and in solvents (e.g. n-propyl alcohol). The depolymerase contained no essential SH groups or essential disulfide bridges and was insensitive to high concentrations of ionic (SDS) and nonionic (Triton and Tween) detergents. Characterization of the cloned structural gene (phaZ7) and the DNA-deduced amino acid sequence revealed no homologies to any PHB depolymerase or any other sequence of data banks except for a short sequence related to the active site serine of serine hydrolases. A classification of the enzyme into a new family (family 9) of carboxyesterases (Arpigny, J. L., and Jaeger, K.-E. (1999) Biochem. J. 343, 177-183) is suggested.

Screening and characterization of trehalose-oleate hydrolyzing lipase

Various soil samples were collected to screen the presence of microorganisms which have ability to degrade TOE. One strain (AKU-883) with good TOE degrading activity was isolated and identified as Burkholderia cepacia and the extracellular enzyme was purified to homogeneity. The purification was achieved by ultrafiltration, Super Q anion-exchange chromatography and Superdex 200HR gel-filtration in the presence of Triton X. The enzyme was purified to 85-fold, and specific activity of 4.910 kU mg protein(-1). The peak preparation on gel filtration showed a single band of 34 kDa on SDS-PAGE and native PAGE which indicate the monomeric nature of the enzyme. The pI of the enzyme was 6.3. The enzyme showed the maximum activity at pH 9 and 65 degrees C, and was stable in the range of pH 5--10 and up to 60 degrees C. Almost all the activity (92%) was kept after incubation for more than 1 week at 50 degrees C (pH 7.3). High activities remained even in water-miscible solvents such as ethanol, dimethyl formamide, diisopropyl ether, and dioxane. The N-terminal 16 amino acid residues were determined as A-N-G-Y-A-A-T-R-Y-P-I-I-L-V-G-G, which showed a consensus sequence for lipases from Burkholderia species. Thus the enzyme was concluded to be a kind of lipase.

Crystal structure of pseudomonas aeruginosa lipase in the open conformation. The prototype for family I.1 of bacterial lipases

The x-ray structure of the lipase from Pseudomonas aeruginosa PAO1 has been determined at 2.54 A resolution. It is the first structure of a member of homology family I.1 of bacterial lipases. The structure shows a variant of the alpha/beta hydrolase fold, with Ser(82), Asp(229), and His(251) as the catalytic triad residues. Compared with the "canonical" alpha/beta hydrolase fold, the first two beta-strands and one alpha-helix (alphaE) are not present. The absence of helix alphaE allows the formation of a stabilizing intramolecular disulfide bridge. The loop containing His(251) is stabilized by an octahedrally coordinated calcium ion. On top of the active site a lid subdomain is in an open conformation, making the catalytic cleft accessible from the solvent region. A triacylglycerol analogue is covalently bound to Ser(82) in the active site, demonstrating the position of the oxyanion hole and of the three pockets that accommodate the sn-1, sn-2, and sn-3 fatty acid chains. The inhibited enzyme can be thought to mimic the structure of the tetrahedral intermediate that occurs during the acylation step of the reaction. Analysis of the binding mode of the inhibitor suggests that the size of the acyl pocket and the size and interactions of the sn-2 binding pocket are the predominant determinants of the regio- and enantio-preference of the enzyme.

Kinetics and mechanisms of reactions catalyzed by immobilized lipases*

This review focuses on the kinetics of several modes of immobilization of lipases, on the mechanisms of reactions of activation of immobilized lipases, and on the kinetics and mechanisms of reactions catalyzed by immobilized lipases. A comprehensive overview of the state of the art pertaining to structural features of lipases is provided as an aid to understand immobilization, interfacial activation, and catalytic performance. General rate expressions are duly derived; more frequent simplifying assumptions are stated and the results thereof listed. Physicochemical and statistical significance of parameters in rate expressions fitted to experimental data are also discussed whenever possible.

In vitro analysis of roles of a disulfide bridge and a calcium binding site in activation of Pseudomonas sp. strain KWI-56 lipase

The expression of lipase from Pseudomonas sp. strain KWI-56 (recently reclassified as Burkholderia cepacia) had been found to be dependent on an activator gene (act) downstream of its structural gene (lip). In this work, the mature lipase was synthesized in an enzymatically active form with a cell-free Escherichia coli S30 coupled transcription-translation system by expressing a recombinant lipase gene (rlip) encoding the mature lipase in the presence of its purified activator or by coexpression of rlip and act. The in vitro expression systems were used for studying the folding process of the lipase. The addition of dithiothreitol in the expression systems decreased the activity dramatically without affecting the synthesis level of the lipase, whereas the in vitro-synthesized active lipase was relatively stable even in the presence of dithiothreitol. This phenomenon was further investigated by constructing mutant lipase genes only in vitro by PCR without gene cloning. Replacements of cysteine residues (Cys190 and Cys270) forming a sole putative disulfide bond to serine residues decreased the lipase activity greatly, suggesting that the disulfide bond was essential for the proper folding of the lipase. In addition, replacing Asp242 and Asp288, which were deduced to be part of a Ca(2+) binding site, also greatly decreased the activities of the in vitro-synthesized lipases. The role of the Ca(2+) binding site in the activation of the lipase is also discussed.

Bacterial biocatalysts: molecular biology, three-dimensional structures, and biotechnological applications of lipases

Bacteria produce and secrete lipases, which can catalyze both the hydrolysis and the synthesis of long-chain acylglycerols. These reactions usually proceed with high regioselectivity and enantioselectivity, and, therefore, lipases have become very important stereoselective biocatalysts used in organic chemistry. High-level production of these biocatalysts requires the understanding of the mechanisms underlying gene expression, folding, and secretion. Transcription of lipase genes may be regulated by quorum sensing and two-component systems; secretion can proceed either via the Sec-dependent general secretory pathway or via ABC transporters. In addition, some lipases need folding catalysts such as the lipase-specific foldases and disulfide-bond-forming proteins to achieve a secretion-competent conformation. Three-dimensional structures of bacterial lipases were solved to understand the catalytic mechanism of lipase reactions. Structural characteristics include an alpha/beta hydrolase fold, a catalytic triad consisting of a nucleophilic serine located in a highly conserved Gly-X-Ser-X-Gly pentapeptide, and an aspartate or glutamate residue that is hydrogen bonded to a histidine. Four substrate binding pockets were identified for triglycerides: an oxyanion hole and three pockets accommodating the fatty acids bound at position sn-1, sn-2, and sn-3. The differences in size and the hydrophilicity/hydrophobicity of these pockets determine the enantiopreference of a lipase. The understanding of structure-function relationships will enable researchers to tailor new lipases for biotechnological applications. At the same time, directed evolution in combination with appropriate screening systems will be used extensively as a novel approach to develop lipases with high stability and enantioselectivity.

Recombinant microbial lipases for biotechnological applications

Lipases, mainly of microbial origin, represent the most widely used class of enzymes in biotechnological applications and organic chemistry. Modern methods of genetic engineering combined with an increasing knowledge of structure and function will allow further adaptation to industrial needs and exploration of novel applications. Production of such tailored lipases requires their functional overexpression in a suitable host. Hence, this article describes the functional heterologous production of commercially important microbial lipases. Based on the knowledge of different lipases' substrate binding sites, the most suitable lipase for a particular application may be selected.

Cloning and sequence analysis of the lipase and lipase chaperone-encoding genes from Acinetobacter calcoaceticus RAG-1, and redefinition of a proteobacterial lipase family and an analogous lipase chaperone family

The genes encoding the lipase (LipA) and lipase chaperone (LipB) from Acinetobacter calcoaceticus RAG-1 were cloned and sequenced. The genes were isolated from a genomic DNA library by complementation of a lipase-deficient transposon mutant of the same strain. Transposon insertion in this mutant and three others was mapped to a single site in the chaperone gene. The deduced amino acid (aa) sequences for the lipase and its chaperone were found to encode mature proteins of 313 aa (32.5kDa) and 347 aa (38.6kDa), respectively. The lipase contained a putative leader sequence, as well as the conserved Ser, His, and Asp residues which are known to function as the catalytic triad in other lipases. A possible trans-membrane hydrophobic helix was identified in the N-terminal region of the chaperone. Phylogenetic comparisons showed that LipA, together with the lipases of A. calcoaceticus BD413, Vibrio cholerae El Tor, and Proteus vulgaris K80, were members of a previously described family of Pseudomonas and Burkholderia lipases. This new family, which we redefine as the Group I Proteobacterial lipases, was subdivided into four subfamilies on the basis of overall sequence homology and conservation of residues which are unique to the subfamilies. LipB, moreover, was found to be a member of an analogous family of lipase chaperones. We propose that the lipases produced by P. fluorescens and Serratia marcescens, which comprise a second sequence family, be referred to as the Group II Proteobacterial lipases. Evidence is provided to support the hypothesis that both the Group I and Group II families have evolved from a combination of common descent and lateral gene transfer.

Biochemical properties of staphylococcal (phospho)lipases

Various staphylococci secrete lipases which require calcium ions for activity, and have profound preferences for substrates with different chain lengths. The lipase from Staphylococcus hyicus is exceptional since it has higher phospholipase than lipase activity. This paper gives an overview of the biochemical properties of these enzymes. It appears that chain length selectivity of these enzymes resides in the acylation step. Interfaces mainly influence the acylation step. Calcium ions do not influence the rate of acylation or deacylation although stabilise the enzyme against denaturation. Molecular modelling based on the X-ray structure of Pseudomonas glumae lipase was used to construct a model of the staphylococcal lipases. With this model the position of serveral residues involved in stubstrate selectivity was predicted. Moreover, a sequence element could be assigned that may function as the so-called lid domain in staphylococcal lipases. Sequence alignment of four staphylococcal lipases, and lipases from P. glumae and Bacillus thermocatenulatus identified several potential calcium ligands, one of which was verified by site directed mutagensesis. It is concluded that stabilisation of lipases by calcium ions might be a more general phenomenon than recognized so far.

A cold-adapted lipase of an Alaskan psychrotroph, Pseudomonas sp. strain B11-1: gene cloning and enzyme purification and characterization

A psychrotrophic bacterium producing a cold-adapted lipase upon growth at low temperatures was isolated from Alaskan soil and identified as a Pseudomonas strain. The lipase gene (lipP) was cloned from the strain and sequenced. The amino acid sequence deduced from the nucleotide sequence of the gene (924 bp) corresponded to a protein of 308 amino acid residues with a molecular weight of 33,714. LipP also has consensus motifs conserved in other cold-adapted lipases, i.e., Lipase 2 from Antarctic Moraxella TA144 (G. Feller, M. Thirty, J. L. Arpigny, and C. Gerday, DNA Cell Biol. 10:381-388, 1991) and the mammalian hormone-sensitive lipase (D. Langin, H. Laurell, L. S. Holst, P. Belfrage, and C. Holm, Proc. Natl. Acad. Sci. USA 90:4897-4901, 1993): a pentapeptide, GDSAG, containing the putative active-site serine and an HG dipeptide. LipP was purified from an extract of recombinant Escherichia coli C600 cells harboring a plasmid coding for the lipP gene. The enzyme showed a 1,3-positional specificity toward triolein. p-Nitrophenyl esters of fatty acids with short to medium chains (C4 and C6) served as good substrates. The enzyme was stable between pH 6 and 9, and the optimal pH for the enzymatic hydrolysis of tributyrin was around 8. The activation energies for the hydrolysis of p-nitrophenyl butyrate and p-nitrophenyl laurate were determined to be 11.2 and 7.7 kcal/mol, respectively, in the temperature range 5 to 35 degrees C. The enzyme was unstable at temperatures higher than 45 degrees C. The Km of the enzyme for p-nitrophenyl butyrate increased with increases in the assay temperature. The enzyme was strongly inhibited by Zn2+, Cu2+, Fe3+, and Hg2+ but was not affected by phenylmethylsulfonyl fluoride and bisnitrophenyl phosphate. Various water-miscible organic solvents, such as methanol and dimethyl sulfoxide, at concentrations of 0 to 30% (vol/vol) activated the enzyme.