The folding and activity of the extracellular lipase of Rhizopus oryzae are modulated by a prosequence

The fungus Rhizopus oryzae synthesizes an extracellular lipase precursor bearing N-terminal pre- and pro-sequences. Our studies in Escherichia coli and using recombinant lipase in vitro indicate that the prosequence of 97 amino acids has at least two functions. First, it modulates the enzyme activity of the lipase so that this enzyme can initially be synthesized in a non-destructive form. Direct synthesis of the mature form of the lipase in the cell has toxic consequences, at least partly because of phospholipase activity that is suppressed in the proprotein. Secondly, it supports folding of the lipase via a pathway influenced by a single cysteine residue at position - 68. Mutational analysis of the prosequence demonstrates not only the key role of this cysteine residue but also the importance of the neighbouring amino acids. In particular, Arg-69 probably enhances the leaving group character of Cys-68. We propose a model in which Cys-68 acts as an intramolecular thiodisulphide reagent, playing a catalytic role in the folding of the enzyme. The prosequence is capable of performing the described functions both in cis and in trans.

Crystal structure of a bacterial lipase from Chromobacterium viscosum ATCC 6918 refined at 1.6 angstroms resolution

The crystal structure of a lipase from the bacterium Chromobacterium viscosum ATCC 6918 (CVL) has been determined by isomorphous replacement and refined at 1.6 angstroms resolution to an R-factor of 17.8%. The lipase has the overall topology of an alpha/beta type protein, which was also found for previously determined lipase structures. The catalytic triad of the active center consists of the residues Ser87, Asp263 and His285. These residues are not exposed to the solvent, but a narrow channel connects them with the molecular surface. This conformation is very similar to the previously reported closed conformation of Pseudomonas glumae lipase (PGL), but superposition of the two lipase structures reveals several conformational differences. r.m.s. deviations greater than 2 angstroms are found for the C alpha-atoms of the polypeptide chains from His15 to Asp28, from Leu49 to Ser54 and from Lys128 to Gln158. Compared to the PGL structure in the CVL structure, three alpha-helical fragments are shorter, one beta-strand is longer and an additional antiparallel beta-sheet is found. In contrast to PGL, CVL displays an oxyanion hole, which is stabilized by the amide nitrogen atoms of Leu17 and Gln88, and a cis-peptide bond between Gln291 and Leu292. CVL contains a Ca2+, like the PGL, which is coordinated by four oxygen atoms from the protein and two water molecules.

Development and evaluation of a dipstick immunoassay format for the determination of atrazine residues on-site

On the basis of a semi-quantitative dipstick immunoassay (IA) for atrazine with visual detection (Giersch, T., J. Agric. Food Chem., 1993, 41, 1006), a quantitative format suitable as a field assay for the analysis of pesticide residues in water and liquid food samples on-site is described. For antibody immobilization, different membranes and immobilization techniques were investigated. The measuring range for atrazine was 0.3-10 micrograms l-1 using reflectance detection. The total assay time was about 25 min with dipsticks previously coated with antibody. Atrazine-spiked water and liquid food samples were selected for assay evaluation. The samples could be measured directly without the need for any prior enrichment or clean-up steps. A satisfactory agreement was found between the results of the dipstick IA and HPLC or GC measurements of both the original and spiked samples.

Purification and some properties of a novel microbial lactate oxidase

Geotrichum candidum was found to produce a lactate oxidase. The enzyme was purified by gel filtration and ion-exchange chromatography. The purified lactate oxidase showed a molecular mass of 50 kDa under denaturing and about 400 kDa under non-denaturing conditions. Transmission electron microscopy analysis confirmed an octameric structure. FMN was found to be a cofactor for this enzyme. Polarographic studies confirmed an oxygen uptake by the lactate oxidase. The enzyme showed specificity towards the L isomer of lactate and did not oxidise pyruvate, fumarate, succinate, maleate and ascorbate. It was stable at alkaline pH and also for 15 min at 45 degrees C. The addition of glycerol and dextran 500,000 to the enzyme sample enhanced storage stability.

Analysis of the catalytic mechanism of a fungal lipase using computer-aided design and structural mutants

Both an active enzyme conformation and stabilization of tetrahedral transition states are essential for the catalysis of ester bond hydrolysis by lipases. X-ray structural data and results from site-directed mutagenesis experiments with proteases have been used as a basis for predictions of amino acid residues likely to have key functions in lipases. The gene encoding a lipase from Rhizopus oryzae was cloned and expressed in Escherichia coli. Site-directed mutagenesis of this gene was used to test the validity of computer-aided predictions of the functional roles of specific amino acids in this enzyme. Examination of the kinetic constants of the Rhizopus oryzae lipase variants allowed us to identify amino acid residues which are directly involved in the catalytic reaction or which stabilize the active geometry of the enzyme. The combination of these results with molecular mechanics simulations, based on a homology-derived structural model, provided new information about structure-function relationships. The interpretation of the data is consistent with results obtained with other hydrolases, such as proteases.

Alpha-branched 1,2-diacyl phosphatidylcholines as effectors of activity of cytochrome P450SCC (CYP11A1). Modeling the structure of the fatty acyl chain region of cardiolipin

Cardiolipin has been shown to be the most effective activator of cholesterol side chain cleavage activity of cytochrome P450SCC, and evidence has been provided for a lipid effector site on the enzyme. Results suggested the headgroup of cardiolipin as major determinant of lipid interaction with P450SCC (Lambeth, J. D. (1981) J. Biol. Chem. 256, 4757-4762). The role of unsaturation is contradictory and open to question (Igarashi, Y. and Kimura, T. (1986) Biochemistry 25, 6461-6466). We synthesized phosphatidylcholines with fully saturated branched fatty acyl chains substituted in the 2-positions of the main chains and studied the influence of these lipids on the activity and other properties of P450SCC in vesicle-reconstituted systems. These saturated branched lipids, with regard to the fatty acyl moiety in molecular shape similar to cardiolipin but with the headgroup of phosphatidylcholines retained, showed a stimulatory efficiency higher than any other phospholipid and at least comparable to cardiolipin. Activation is sensitive to the acyl chain structure and composition. Results suggest that the shape of the molecule at least partially plays an important role in the process of stimulation of the activity of P450SCC. Because binding of cholesterol was increased by the branched lipids monitored optically by the fraction of P450SCC in the high spin form, it was concluded that these lipids, like cardiolipin and other lipids, exert their effects by regulating the binding of cholesterol to P450SCC. These data suggest that polymorphic lipids such as branched phosphatidylcholines and cardiolipin might influence P450SCC function by maintenance of the membrane curvature at a value optimal for activity.

Thermoalkalophilic lipase of Bacillus thermocatenulatus. I. molecular cloning, nucleotide sequence, purification and some properties

An expression library was generated by partial Sau3A digestion of genomic DNA from the thermophile Bacillus thermocatenulatus and cloning of DNA fragments in pUC18 in Escherichia coli DH5alpha. Screening for lipase activity identified a 4.5 kb insert in pUC18 which directed the production of lipase in E. coli DH5alpha. A subclone with a 2.2 kb insert was sequenced. The lipase gene codes for a mature lipase of 388 amino acid residues, corresponding to a molecular weight of 43 kDa. As in other Bacillus lipases, an Ala replaces the first Gly in the conserved pentapeptide Gly-X-Ser-X-Gly found in most lipases. The region upstream of the lipase gene contains a Bacillus promoter which directs the expression of lipase in E. coli DH5alpha. The expressed lipase was isolated and purified 312-fold to homogeneity. N-terminal sequencing of the purified lipase revealed a correct cleavage of the preprotein in E. coli DH5alpha. Maximum activity was found at pH 8.0-9.0 with tributyrin and olive oil as substrates and at 60-70 degrees C with p-NPP and olive oil as substrates. The lipase showed high stability at pH 9.0-11.0 and towards various detergents and organic solvents.

Crystal structure of NADH oxidase from Thermus thermophilus

The crystal structures of the flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) containing isoforms of NADH oxidase from Thermus thermophilus have been determined by isomorphous and molecular replacement and refined to 2.3 A and 1.6 A resolution with R-values of 18.5% and 18.6% respectively. The structure of the homodimeric enzyme consists of a central 4-stranded antiparallel beta-sheet covered by helices, a more flexible domain formed by two helices, and a C-terminal excursion connecting the subunits. The active sites are located in a deep cleft between the subunits. The binding site of the flavin cofactor lacks the common nucleotide binding fold and is different from the FMN binding site found in flavodoxins.

The design of enzyme sensors based on the enzyme structure

The size of some of the reported electron mediators for glucose oxidase compared with the available space to penetrate the active site, implies that electrons have to move along the protein structure. Theoretical and experimental evidence predicts that it is possible to have electron transfer at the required rate used in biosensors (200 to 1840 electrons s-1) for the distances in glucose oxidase (20 to 25 A). Use of the program "Pathways" (together with the knowledge of the enzyme structure) allowed us to find an electron pathway within the enzyme. This pathway has a maximum electron coupling between the active site and the surface of the enzyme. The pathway reaches the surface near functional groups that can be used for oriented immobilization of the enzyme. Experimental confirmation of this particular pathway has been attempted but it is still elusive.

On-line monitoring of glucose, glutamate and glutamine during mammalian cell cultivations

Amperometric biosensors (based on rhodinised carbon electrodes) for glucose, glutamine and glutamate were constructed. The sensors were incorporated into a three cell parallel FIA system and used to monitor the three analytes on-line during two mammalian cell perfusion cultures. All measurements were made simultaneously from undiluted media sample. Use of the FIA system enabled easy and rapid exchange of the sensors, during cultivation. The inclusion of a calibration step, regularly for all sensors, helped to maintain the accuracy of all measurements. Comparison with off-line measurements indicated that all three biosensors operated successfully, providing accurate information.

Interactions between aldehyde derivatives and the aldehyde binding site of bacterial luciferase

The interaction of triazine aldehydes with the aldehyde binding site of bacterial luciferases was investigated using a series of triazine aldehydes with different aldehyde chain length, and substituents on the s-triazine ring. Substrate activity was determined using luciferase from Photobacterium fischeri and Vibrio harveyi in a dithionite-based luciferases assay. The chain length optimum was determined for two triazine aldehyde classes to be C-10 and C-11, respectively. Only the substrate activity of 10-(4-chloro-6-methylthio-s-triazine-2-yl)aminodecanal (5) was as high as n-decanal, the reference aldehyde. All other triazine derivatives reduced light emission, probably by hindered binding of the substrates. The degree of activity reduction correlated with the volume of the triazine ring moiety. The triazine moiety volume of compound 5 was estimated to be 200 x 10(-30) m3. Triazine aldehydes which showed reduced light emission had an estimated volume of 228 x 10(-30) m3 or greater. All triazine aldehydes showed approximately 10-fold lower activities for Vibrio harveyi than for Photobacterium fischeri luciferase. Substrate specificity was the same for both luciferases. A schematic superposition of quinone aldehydes and triazine aldehydes which showed substrate activities equivalent to n-decanal, indicated potential interaction sites of aldehyde substrates with the aldehyde binding site of bacterial luciferases. The in vivo relevance of the results is discussed.

Improved properties of bovine erythrocyte acetylcholinesterase, isolated by papain cleavage

A simple and rapid procedure involving papain cleavage of the membrane anchor was used to isolate membrane-bound acetylcholinesterase from bovine erythrocytes. The solubilized enzyme was purified 930-fold by ion exchange chromatography and gel filtration. The properties of the papain-cleaved acetylcholinesterase were compared with those of a commercial acetylcholinesterase, solubilized from the erythrocyte membranes by detergents. Cleavage of the membrane anchor eliminated dimer aggregation, caused a pH shift in thermal stability and resulted in increased stability in organic solvents. Bovine serum albumin, used as stabilizer of the commercial enzyme preparation, increased the thermal stability but concomitantly decreased the activity of acetylcholinesterase at pH 6-8. The improved stability of the cleaved acetylcholinesterase, especially in organic solvents, may enhance the biosensor performance of the enzyme.

Screening, purification and properties of a thermophilic lipase from Bacillus thermocatenulatus

By screening of 15 thermophilic Bacillus strains, five strains exhibiting lipase activity were found. Among these the strain Bacillus thermocatenulatus (DSM 730) produced the highest lipase activity. The lipase proved to be inducible and extracellular and was purified 67-fold to homogenous state by hexane extraction, methanol precipitation and ion-exchange chromatography on Q-Sepharose. The molecular weight of the lipase determined by SDS-PAGE is 16 kDa. However, the lipase forms very large aggregates (> 750 kDa) as observed after native PAGE, which makes handling of the lipase very difficult. The lipase binds almost irreversibly on different chromatography matrices, e.g., Amberlite and Serolite, and is very stable in the immobilised form. The N-terminal sequence consists of 53% apolar amino acids and shows no significant homology towards other known lipase sequences. Maximum activity was found at pH 7.5-8.0 and 60-70 degrees C with pNPP and olive oil as substrates.

Properties of unusual phospholipids, II: Synthesis, NMR studies and monolayer investigations of diacylglycerophosphocholines containing alpha-branched acyl chains

Diacylglycerophosphocholines, containing various alpha-branched fatty acids, were synthesized and purified to homogeneity. The influence of the alpha-branched acyl chains on the monolayer packing properties of these phospholipids was studied by the Langmuir-Blodgett film balance technique. NMR investigations were used for conformational studies, including the determination of rotamer populations about the dihedral angles (theta 2, theta 4 and alpha 1) in the glycerol region of the diacylglycerophosphocholines.

Properties of unusual phospholipids: I. Synthesis, monolayer investigations and calorimetry of diacylglycerophosphocholines containing monoacetylenic acyl chains

Isomeric diacylglycerophosphocholines containing various octadecynoic acids (4-, 6-, 9-, 12-, 14- and 17-octadecynoic acid) were synthesized and purified to homogeneity. Their behaviour in monolayers, when studied by the Langmuir-Blodgett film balance technique, revealed systematic relationships between structure and packing properties. The thermotropic phase behaviour of these novel phospholipids, as measured by differential scanning calorimetry, depended in a systematic fashion on the position of the triple bond: the gel-to-liquid-crystalline phase transition temperature (Tm) passed through a minimum of -3.4 degrees C for a triple bond in position 9.

Crystallization and preliminary X-ray analysis of a lipase from Chromobacterium viscosum

Lipase from Chromobacterium viscosum has been purified to homogeneity and crystallized in a form suitable for X-ray diffraction analysis from 10-14% polyethylene glycol 4000 and 10-14% 2-methyl-2,4-pentane diol at pH 6.4 in the presence of 0.25%(w/v) n-octyl-beta-D-glucopyranoside. These crystals belong to space group P2(1)2(1)2 with refined lattice constants a = 41.1 A, b= 156.8, c = 43.6 A, indicating a cell content of one monomer per asymmetric unit of the crystal. The crystals diffract to a resolution of 2.2 A.

On-line monitoring of monoclonal antibody production with regenerable flow-injection immuno systems

In this paper two systems for the observation of the production of mouse-IgG during the cultivation of hybridoma cells in a perfusion reactor are presented. The direct immunosystem is based on the detection of changes in capacitance of a dielectric layer (tantalum oxide) on a metal surface (tantalum) when antibodies bind to immobilized anti-antibodies. The sensor consisted of a 25 nm tantalum oxide layer, electrochemically grown onto a laser patternized 1 micron thick tantalum layer. The indirect system is based on an automated fluorimetric sandwich ELISA system with beta-galactosidase conjugated secondary antibodies. Two cultivations of mouse hybridoma cells in a 2-1 perfusion reactor were performed. The first cultivation was monitored with the capacitance system, the second cultivation was monitored with the fluorimetric system.

A structural model of mono- and diacylglycerol lipase from Penicillium camembertii

The amino acid sequence of lipase from Penicillium camembertii was aligned with Rhizomucor miehei lipase without permitting any deletion or insertion in the structurally conserved regions. This lipase was classified into the R. miehei lipase family, because 33% of the residues were identical and 18% of the exchanges were conserved. A graphic molecular model for P. camembertii lipase was built using information from the sequence and X-ray structure of R. miehei lipase. The primary specificity pocket in the model of P. camembertii lipase predicted a substrate preference for monoacylglycerols and diacylglycerols. The close region to reactive His259 in P. camembertii lipase, which located in the opposite shore to the helical lid that was predictable to move in the activated state, contributed to the decision of the unique substrate specificity.

Comparison of different biosensor systems suitable for bioprocess monitoring

To achieve effective bioprocess monitoring, sensing systems are required which are suitable for an on-line determination of substrates, inhibitors, nutrients or products. Such devices may utilise biochemical principles, i.e. the specific interaction of biochemical receptors with their surroundings. They can be constructed either as in situ sensors or as flow-through sensors connected to the process via sampling devices. Hence, characteristic features of an in situ glucose electrode are described, e.g. analytical range, sensitivity and stability. The sensor was based on mediated electron transfer from the enzyme glucose oxidase to the graphite electrode, the mediators being tetrathiafulvalene (TTF) or dimethylferrocene (DMF). Additionally, various flow injection analysis (FIA) systems based on oxidases, which were immobilised either on controlled pore glass or in a membrane, were characterised with respect to analytical ranges and sensitivities and applied to glucose, lactate and glutamate determinations in off-line samples taken from an animal cell cultivation.

Enhancement of immunoassay sensitivity by molecular modification of competitors

The potential of weak competitors to enhance the sensitivity of competitive immunoassays is described. Several triazine derivatives have been analyzed for their use as competitors. Their binding properties were determined using an enzyme-linked immunosorbent assay (ELISA) with a monoclonal antibody specific to triazines. Selected derivatives were immobilized onto the surface of a fibre optic sensor and atrazine was determined in a competitive manner using a fluorescein-labelled antibody. Using the weak binding competitor 11-(4-ethylamino-6-methylthio-s-triazine-2-yl)undecanoic acid (TE11S) the detection limit for atrazine could be lowered 100-fold in comparison to 2-aminohexylamino-4-ethylamino-6-isopropylamino-s-triazine (AHA), the previously used competitor.

Purification and properties of a lipase from Penicillium expansum

Penicillum expansum DSM 1994 produces a new, inducible extracellular lipase when grown in medium containing 0.1% olive oil. Maximum activity was obtained after 4 days of incubation at 20 degrees C. The enzyme was purified 219-fold by cross-flow filtration, ammonium sulfate precipitation and hydrophobic interaction chromatography to a final specific activity of 558 U/mg. The molecular weight of the homogeneous lipase was (25 kDa) determined by gel filtration and SDS-PAGE, however, it forms active dimers and higher aggregates as observed after native PAGE. The enzyme was identified as a glycoprotein with a pI of 5.5. The N-terminal sequence shows a homology to sequences of other lipase just behind their consensus sequence. Enzyme stability was enhanced by the addition of Tween 20 and Lubrol PX. The enzyme showed a maximum activity at pH 9 at 45 degrees C and was stable at a broad pH range of 6-10. Lipase of P. expansum showed a preference for triacylglycerols, but no positional specificity.

Matrix-assisted ultraviolet laser desorption/ionization mass spectrometry applied to multiple forms of lipases

Matrix-assisted ultraviolet laser desorption/ionization mass spectrometry was used to investigate heterogeneous patterns and molecular masses of microbial lipases from Penicillium camembertii, Geotrichum candidum, and Pseudomonas sp. Mass spectral peaks of the native, glycosylated lipases from P. camembertii and G. candidum were broader than those of the corresponding deglycosylated enzymes, indicative of heterogeneous glycosylations. The broader peaks in the mass spectra were caused by an overlapping of unresolved peaks, derived from single glycoprotein species. Molecular masses determined for the deglycosylated proteins were in excellent agreement with those deduced from amino acid composition and sequence data, whereas with conventional biochemical methods (gelfiltration, sodium dodecyl sulfate-polyacrylamide gel electrophoresis) only very rough estimations of molecular masses were possible. By mass spectrometric analysis of the four fractions of chromatographically separated P. camembertii lipase molecular masses of 29,990, 34,030, 31,990, and 32,140 Da were found before and 29,960, 29,980, 29,990 and 30,010 Da, respectively, after deglycosylation. Thus from the four native fractions of P. camembertii lipase three were glycoproteins. G. candidum lipase showed an average molecular mass of 63,500 Da for the heterogeneously deglycosylated native form and a molecular mass of 59,650 Da for the deglycosylated enzyme. For the Pseudomonas lipase, which could only be isolated with lipids firmly attached, a molecular mass of 32,890 Da was determined, in close agreement with that derived from the cDNA sequence.