Molecular weight and substrate characteristics of human serum arylesterase following purification by immuno-affinity chromatography

Human serum arylesterase (EC 3.1.1.2) was purified over 400-fold with a recovery of 61-78% by single-step immuno-affinity chromatography using a monoclonal antibody, 12-1H8, as the adsorbent. The resultant preparation behaved as one component on SDS-PAGE with an apparent M(r) of 46,000, indicating its high homogeneity. Molecular weight was determined as 380,000 Da by HPLC on TSK-gel G-3000SW. The arylesterase molecule would thus appear to be comprised of octameric subunits. The purified protein hydrolyzed paraoxon. The present study suggests that a separate classification of EC 3.1.8.1 for its paraoxon hydrolyzing activity may not be appropriate to differentiate from arylesterase activity. In addition, the substrate for arylesterase is discussed in terms of its chemical structure.

Ferulic acid esterase from Aspergillus niger: purification and partial characterization of two forms from a commercial source of pectinase

Two forms of ferulic acid esterase from Aspergillus niger have been isolated from a commercial source of pectinase. One, designated I, has a M(r) of 132,000, is probably dimeric, and has a pI of 3.0. The second, designated II, was partially purified and is monomeric (M(r) 29,000), with a pI of 3.6. Both enzymes were free of pectinase and xylanase activity and released ferulic acid from methyl ferulate. In association with a xylanase, they also released ferulic acid from destarched wheat bran. Ferulic acid esterase II released a small amount of ferulic acid (0.09 unit/mg of protein) in the absence of xylanase. The enzymes had different specificities for a range of methyl ester derivatives of cinnamoyl and benzoyl acids, acetylated xylan and p-nitrophenyl acetate.

Dienelactone hydrolase from Pseudomonas cepacia

Dienelactone hydrolases have previously been shown to play a crucial role in chlorocatechol degradation via the modified ortho cleavage pathway. Recently, the enzymes induced in 4-fluorobenzoate-utilizing bacteria have been classified into three groups on the basis of their specificity towards cis- and trans-dienelactone. The dienelactone hydrolase and the 3-oxoadipate enol-lactone hydrolase from Pseudomonas cepacia have now been purified to apparent homogeneity and characterized with respect to molecular mass and amino acid composition. The dienelactone hydrolase has a distinct preference for cis-dienelactone and did not convert the trans isomer or muconolactone, 3-oxoadipate enol-lactone, or 4-fluoromuconolactone to a significant extent. In properties like amino acid composition, pH optimum of activity, and lack of inhibition by p-chloromercuribenzoate, the P. cepacia dienelactone hydrolase differed substantially from 3-oxoadipate enol-lactone hydrolases and other dienelactone hydrolases.

Crystallization and preliminary X-ray crystallographic analysis of carboxylesterase from pseudomonas fluorescens

Large crystals of carboxylesterase from Pseudomonas fluorescens have been grown in the presence of dioxane using ammonium sulfate and lithium sulfate as precipitant. They belong to the tetragonal space group P4(1)2(1)2 (or P4(3)2(1)2), with unit cell dimensions of a = 82.01 (+/-0.06) A and c = 145.44 (+/- 0.08) A. The presence of one carboxylesterase dimer in the asymmetric unit gives the crystal volume per protein mass (VM) of 2.56 A3/Da and solvent fraction of 52.0% by volume. The crystals diffract to at least 2.3 A Bragg spacing when exposed to CuK alpha X rays from a rotating anode generator. X-ray data (nearly complete to 2.6 A Bragg spacing) have been collected from a native crystal.

Catalysis by dienelactone hydrolase: a variation on the protease mechanism

Dienelactone hydrolase (DLH), an enzyme from the beta-ketoadipate pathway, catalyzes the hydrolysis of dienelactone to maleylacetate. Our inhibitor binding studies suggest that its substrate, dienelactone, is held in the active site by hydrophobic interactions around the lactone ring and by the ion pairs between its carboxylate and Arg-81 and Arg-206. Like the cysteine/serine proteases, DLH has a catalytic triad (Cys-123, His-202, Asp-171) and its mechanism probably involves the formation of covalently bound acyl intermediate via a tetrahedral intermediate. Unlike the proteases, DLH seems to protonate the incipient leaving group only after the collapse of the first tetrahedral intermediate, rendering DLH incapable of hydrolyzing amide analogues of its ester substrate. In addition, the triad His probably does not protonate the leaving group (enolate) or deprotonate the water for deacylation; rather, the enolate anion abstracts a proton from water and, in doing so, supplies the hydroxyl for deacylation.

Degradation of poly(3-hydroxyoctanoic acid) [P(3HO)] by bacteria: purification and properties of a P(3HO) depolymerase from Pseudomonas fluorescens GK13

Twenty-five gram-negative bacteria and one gram-positive bacterium capable of growing on poly(3-hydroxyoctanoic acid) [P(3HO)] as the sole source of carbon and energy were isolated from various soils, lake water, and activated sludge. Most of the isolates degraded only P(3HO) and copolymers of medium-chain-length (MCL) hydroxyalkanoic acids (HA). Except for the gram-positive strain, which was able to hydrolyze P(3HO) and poly(3-hydroxybutyric acid) [P(3HB)], no isolate was able to degrade polymers of short-chain-length HA, such as P(3HB) or poly(3-hydroxyvalerate) [P(3HV)]. All strains utilized a large variety of monomeric substrates for growth. All gram-negative strains, but not the gram-positive strain, accumulated poly(hydroxyalkanoic acids) (PHA), consisting of MCL HA, if they were cultivated under accumulation conditions. One strain, which was identified as Pseudomonas fluorescens GK13 (biovar V), was selected and the extracellular P(3HO) depolymerase of this strain was purified from the culture medium of P(3HO)-grown cells by chromatography with Octyl-Sepharose CL4B and by gel filtration with Superose 12. The relative molecular weights of the native and sodium dodecyl sulfate-treated enzymes were 48,000 and 25,000, respectively. The purified enzyme hydrolyzed P(3HO), copolymers of MCL HA, and para-nitrophenyl esters of fatty acids. P(3HB), P(3HV), and characteristic substrates for lipases, such as Tween 80 or triolein, were not hydrolyzed. The P(3HO) depolymerase of P. fluorescens GK13 was insensitive to phenylmethylsulfonyl fluoride and dithioerythritol, unlike other PHA depolymerases. The dimeric ester of 3-hydroxyoctanoic acid was identified as the main product of enzymatic hydrolysis of P(3HO).(ABSTRACT TRUNCATED AT 250 WORDS)

Preliminary X-ray study of naproxen esterase from Bacillus subtilis

Single crystals of naproxen esterase from Bacillus subtilis have been obtained from PEG6000 solutions at pH 8.0 by liquid-liquid diffusion while applying a temperature gradient from 4 degrees C to room temperature over a period of four weeks. The crystals belong to the trigonal space group P3(1)21 or P3(2)21 with a = b = 47.59 A and c = 212.91 A. The asymmetric part of the unit cell contains one protein molecule with M(r) = 33,771. The crystals diffract to at least 3.0 A resolution and are suitable for an X-ray structure analysis.

Isolation and characterization of an extracellular glycosylated protein complex from Clostridium thermosaccharolyticum with pectin methylesterase and polygalacturonate hydrolase activity

An extracellular protein complex was isolated from the supernatant of a pectin-limited continuous culture of Clostridium thermosaccharolyticum Haren. The complex possessed both pectin methylesterase (EC 3.1.1.11) and exo-poly-alpha-galacturonate hydrolase (EC 3.2.1.82) activity and produced digalacturonate from the nonreducing end of the pectin chain. The protein consisted of 230- and 25-kDa subunits. The large subunit contained 10% (wt/wt) sugars (N-acetylgalactosamine and galactose). Under physiological conditions both activities acted in a coordinated manner: the ratio between methanol and digalacturonate released during degradation was constant and equal to the degree of esterification of the pectin used. Prolonged incubation of the enzyme with pectin led to a nondialyzable fraction that was enriched in neutral sugars, such as arabinose, rhamnose, and galactose; the high rhamnose/galacturonic acid ratio was indicative of hairy region-like structures. The smallest substrate utilized by the hydrolase was a tetragalacturonate. Vmax with oligogalacturonates increased with increasing chain length. The Km and Vmax for the polygalacturonate hydrolase with citrus pectate as a substrate were 0.8 g liter-1 and 180 mumol min-1 mg of protein-1, respectively. The Km and Vmax for the esterase with citrus pectin as a substrate were 1.2 g liter-1 and 440 mumol min-1 mg of protein-1, respectively. The temperature optima for the hydrolase and esterase were 70 and 60 degrees C, respectively. Both enzyme activities were stable for more than 1 h at 70 degrees C. The exo-polygalacturonate hydrolase of Clostridium thermosulfurogenes was partially purified while the methylesterase was also copurified.

Characterization of rat plasma esterase ES-1A concerning its molecular and catalytic properties

To characterize esterase ES-1A from rat plasma with regard to its molecular and catalytic properties, the enzyme was purified. The degree of purification, as measured by a densitometric gel scanning assay for ES-1 activity, was about 142-fold with a recovery of 9%. The ES-1A preparation was free of other plasma esterases but not of other plasma proteins. The enzyme shows microheterogeneity after staining for esterase activity in gradient polyacrylamide gel electrophoresis and isoelectric focusing. The native ES-1A protein is a carboxylesterase (EC 3.1.1.1) with a molecular mass of about 59 kDa as determined by gel filtration and gradient polyacrylamide gel electrophoresis. ES-1A exhibits a pI of 4.73 and optimum pH of 8.6 for p-nitrophenylbutyrate hydrolysis. With various p-nitrophenyl esters as substrate for ES-1A, it was found that the Michaelis constant decreased with increasing number of C atoms of the unbranched fatty acid moiety, whereas the maximum reaction velocity peaked with p-nitrophenylvalerate. The high degree of similarity of the properties of rat ES-1A with those reported earlier for mouse ES-2B, rabbit EST-2F, and human ESB2 suggests that these four esterases have a common evolutionary origin.

Characterization of two major isoforms of juvenile hormone esterase from Trichoplusia ni (Lepidoptera)

The two major isoforms of juvenile hormone (JH) esterase isolated from Trichoplusia ni were fragmented by cyanogen bromide and trypsin digestion. The resulting CNBr or CNBr/trypsin fragments were characterized and compared biochemically by SDS-PAGE, isoelectric focusing, two-dimensional electrophoresis and HPLC. Similar and unique fragments were examined for sequence, antigenic determinants and carbohydrate moieties. The studies identified small regions of the proteins which possess either potentially different sequences or different post-translational modifications. The location of a glycosylated asparagine residue was determined, as well as a region containing an epitope probably composed of a linear sequence of residues. An N-terminal region was identified that contained charge variation between the two isoforms and the sequence was obtained for the only unique CNBr/trypsin fragment detected from that region. These are the first data on mapping of regions of charge variation, epitope location and glycosylation sites for this enzyme from any insect species.

Crystallization and preliminary X-ray crystallographic analysis of arylesterase from Pseudomonas fluorescens

Large crystals of arylesterase from Pseudomonas fluorescens have been grown at room temperature using ammonium sulfate as a precipitant. They grow to dimensions of 0.7 x 0.7 x 0.6 mm3 within a month. The crystals belong to the trigonal space group P3(1) (or P3(2)), with unit cell dimensions of a = 147.12 A and c = 131.08 A. The asymmetric unit seems to contain six molecules of dimeric arylesterase, with corresponding crystal volume per protein mass (VM) of 2.53 A3/Da and solvent fraction of 51.5% by volume. The crystals diffract to at least 2.2 A Bragg spacing when exposed to X-rays from a rotating-anode source. X-ray data have been collected to 2.9 A Bragg spacing from native crystals.

The roles of enteric bacterial sialidase, sialate O-acetyl esterase and glycosulfatase in the degradation of human colonic mucin

Sialidase activity in normal faecal extracts showed a preference for mucin-related glycoprotein and oligosaccharide substrates, but the presence of two or more O-acetyl esters at positions C7-C9 on the sialic acids retarded the rate of hydrolysis. A specific sialate O-acetyl esterase was detected with a lower total activity relative to sialidase with mucin substrates and having a pH optimum of 7.8 and a KM of approximately 1 mM sialate O-acetyl ester. A specific glycosulfatase activity was found in faecal extracts using the substrate lactit-[3H]ol 6-O-sulfate with a pH optimum of pH 5.0 and a KM of approximately 1 mM. Faecal extracts from ulcerative colitis (UC) patients had higher sialate O-acetyl esterase and glycosulfatase activity, while mucin sialidase activity was unchanged. Metabolically labelled mucin isolated from UC patients contained less sulfate and had lower sialic acid O-acetylation compared with normal mucin. Colonic mucin was degraded more efficiently by faecal extracts from UC patients compared with normal extracts. The UC mucin was degraded more rapidly than the normal mucin by faecal enzyme extracts from both normal and UC subjects.

Engineering cysteine mutants to obtain crystallographic phases with a cutinase from Fusarium solani pisi

Cutinases are extracellular enzymes involved in the disruption of cutine, an insoluble polyester which covers the surface of plants. They belong to a class of serine esterases that are able to hydrolyse fatty acid esters and emulsified triglycerides as efficiently as lipases, but without displaying interfacial activation. Classical crystallographic methods for obtaining heavy-atom derivatives failed, so the cutinase structure has been solved exclusively by the multiple isomorphous replacement method using four Hg derivatives obtained from mutants S4C, S92C, S120C and S129C. Two of these derivatives behaved as expected: (i) the cys mutant of the catalytic Ser S120C, located at the surface of the active site pocket, leads to a good derivative; and (ii) the Hg atom of the derivative obtained with the S92C mutant is completely accessible to the solvent and occupies two alternative positions--consequently a poor derivative results. In contrast, two mutants show an unexpected behaviour: (i) the Hg atom in the S129C mutant was completely buried 10 A below the protein surface and yielded the best derivative; and (ii) a poor quality derivative was obtained with the S4C mutant. Cys 4 belongs to the disordered propeptide 1-16. The Cys 4 bound Hg atom is located in front of the Asp58 side chain, but neither Cys4 nor parts of the propeptide are clearly visible in the electron density maps of the derivative structure.

An isozyme of microsomal carboxyesterases, carboxyesterase Sec, is secreted from rat liver into the blood

It is generally believed that liver carboxyesterases are localized exclusively in the endoplasmic reticulum (ER), mostly in the lumen, loosely bound to the inner side of the membrane. A cDNA clone, clone (8-1/2-1) supposed to code for one of the isozymes, carboxyesterase E1, was isolated by Takagi et al. [J. Biochem. 104, 801-806 (1988)]. However, the protein coded by clone (8-1/2-1) had no consensus ER retention signal at its carboxy terminus, and the mechanism of its retention by ER lumen was unclear. When clone (8-1/2-1) was expressed in COS cells in this study, the plasmid-coded protein was secreted into the medium. When the carboxy terminal portion of the clone (8-1/2-1)-coded protein was replaced with the corresponding region of another carboxyesterase, pI 6.1 esterase, which had the HVEL sequence at the carboxy terminus, the chimeric protein was retained in the COS cells. We searched for a secretory form carboxyesterase in rat blood immunochemically using polyclonal antibodies to carboxyesterase E1, and detected a cross-reacting protein with a molecular weight of 68 kDa. The molecular weight was decreased by endoglycosidase F treatment but not by endoglycosidase H treatment, indicating that the protein carries complex type sugar chains. In addition, the cross-reacting protein was labeled with [3H] diisopropylfluorophosphate (DFP), suggesting that the protein has an esterase-type active center serine.(ABSTRACT TRUNCATED AT 250 WORDS)

Methionine as translation start signal: a review of the enzymes of the pathway in Escherichia coli

Methionine is the universal translation start but the first methionine is removed from most mature proteins. This review focuses on our present knowledge of the five enzymes sustaining the methionine pathway in translation initiation in Escherichia coli: methionyl-tRNA synthetase, methionyl-tRNA(fMet) formyltransferase, peptidyl-tRNA hydrolase, peptide deformylase and methionine aminopeptidase. The possible significance of retaining methionine as initiation signal is discussed.

Purification and characterization of a novel lactonohydrolase, catalyzing the hydrolysis of aldonate lactones and aromatic lactones, from Fusarium oxysporum

A novel lactonohydrolase, an enzyme that catalyzes the hydrolysis of aldonate lactones to the corresponding aldonic acids, was purified 10-fold to apparent homogeneity, with a 61% overall recovery, from Fusarium oxysporum AKU 3702, through a purification procedure comprising DEAE-Sephacel, octyl-Sepharose CL-4B and hydroxyapatite chromatographies and crystallization. The molecular mass of the native enzyme, as estimated by high-performance gel-permeation chromatography, is 125 kDa, and the subunit molecular mass is 60 kDa. The enzyme contains 15.4% (by mass) glucose equivalent of carbohydrate, and about 1 mol calcium/subunit. The enzyme hydrolyzes aldonate lactones, such as D-galactono-gamma-lactone and L-mannono-gamma-lactone, stereospecifically. Furthermore, it can catalyze the asymmetric hydrolysis of D-pantoyl lactone, which is a promising chiral building block for the chemical synthesis of D-pantothenate. These reactions are reversible, and the reaction equilibrium at pH 6.0 has a molar ratio of nearly 1:1 with D-pantoyl lactone and D-pantoic acid. The Km and Vmax for D-galactono-gamma-lactone are 3.6 mM and 1440 U/mg, respectively, and those for D-galactonate are 52.6 mM and 216 U/mg, respectively. The enzyme also irreversibly hydrolyzes several aromatic lactones, such as dihydrocoumarin and homogentisic-acid lactone.

Purification and properties of an Arthrobacter oxydans P52 carbamate hydrolase specific for the herbicide phenmedipham and nucleotide sequence of the corresponding gene

Arthrobacter oxydans P52 isolated from soil samples was found to degrade the phenylcarbamate herbicides phenmedipham and desmedipham cometabolically by hydrolyzing their central carbamate linkages. The phenylcarbamate hydrolase (phenmedipham hydrolase) responsible for the degradative reaction was purified to homogeneity. The enzyme was shown to be a monomer with a molecular weight of 55,000. A 41-kb wild-type plasmid (pHP52) was identified in A. oxydans P52, but not in a derivative of this strain that had spontaneously lost the ability to hydrolyze phenylcarbamates, indicating that the gene for phenylcarbamate degradation (pcd) is plasmid encoded. Determination of two partial amino acid sequences allowed the localization of the coding sequence of the pcd gene on a 3.3-kb PstI restriction fragment within pHP52 DNA by hybridization with synthetic oligonucleotides. The phenylcarbamate hydrolase was functionally expressed in Escherichia coli under control of the lacZ promoter after the 3.3-kb PstI fragment was subcloned into the vector pUC19. A stretch of 1,864 bases within the cloned Pst fragment was sequenced. Sequence analysis revealed an open reading frame of 1,479 bases containing the amino acid partial sequences determined for the purified enzyme. Sequence comparisons revealed significant homology between the pcd gene product and the amino acid sequences of esterases of eukaryotic origin. Subsequently, it was demonstrated that the esterase substrate p-nitrophenylbutyrate is hydrolyzed by phenmedipham hydrolase.

Cloning and molecular analysis of the poly(3-hydroxyalkanoic acid) gene locus of Pseudomonas aeruginosa PAO1

From genomic libraries, the polyhydroxyalkanoate gene locus of Pseudomonas aeruginosa PAO1 was cloned and characterised at the molecular level. Two genes coding for polyhydroxyalkanoate synthases, phaC1Pa and phaC2Pa, a polyhydroxyalkanoate depolymerase gene, phaDPa, and four adjacent open reading frames (ORF1, ORF2, ORF3 and ORF4) were identified from the nucleotide sequence. Two transcriptional start sites, which were preceded by sequences resembling the Escherichia coli consensus sequences for sigma 54 and sigma 70 promoters, were identified experimentally upstream of phaC1Pa, which was shown by Northern blot analysis to constitute an operon together with phaDPa. A third putative promoter resembling the E. coli consensus sequence for sigma 70-dependent promoters was proposed upstream of phaC2Pa, which is in a bicistronic operon with ORF3. Investigations of rpoN-negative mutants of related strains revealed that polyhydroxyalkanoate accumulation from gluconate required an intact rpoN locus in P. aeruginosa. Complementation experiments revealed multiple evidence that either polyhydroxyalkanoate synthase is involved in polyhydroylkanoate accumulation from gluconate as well as from octanoate. The P. aeruginosa PAO1 polyhydroxyalkanoate gene locus was expressed in the polyhydroxyalkanoate-negative mutant Alcaligenes eutrophus PHB-4 and in the poly(3-hydroxybutyrate)-accumulating strain P. oleovorans DSM1045. It conferred on the latter the ability to synthesize and accumulate polyhydroxyalkanoates consisting of medium-chain-length 3-hydroxyalkanoic acids from unrelated substrates in addition to poly(3-hydroxybutyrate). The sequence of the putative translational product of ORF1 was similar to those of the leukotoxin repressor of Pasteurella haemolytica and to the ORF9 product of Azotobacter vinelandii, and that of ORF4 was similar to the algP product of P. aeruginosa and to eukaryotic histone H1 proteins. The proteins of ORF2 and ORF3 appear to be previously unidentified.

Disulfide bridges in tomato pectinesterase: variations from pectinesterases of other species; conservation of possible active site segments

Analysis of tomato pectinesterase by carboxymethylation, with and without reduction, shows that the enzyme has two intrachain disulfide bridges. Analysis of fragments obtained from the native enzyme after digestion with pepsin identified bridges connecting Cys-98 with Cys-125, and Cys-166 with Cys-200. The locations of disulfide bridges in tomato pectinesterase are not identical to those in three distantly related pectinesterases (18-33% residue identities) from microorganisms. However, one half-Cys (i.e., Cys-166) position is conserved in all four enzymes. Sequence comparisons of the overall structures suggest a special importance for three short segments of the entire protein. One segment is at the N-terminal part of the tomato pectinesterase, another in the C-terminal portion near the distal end of the second disulfide loop, and the third segment is located in the central part between the two disulfide bridges. The latter segment, encompassing only 40 residues of the entire protein, appears to high-light a functional site in a midchain segment.

The carboxylesterase family exhibits C-terminal sequence diversity reflecting the presence or absence of endoplasmic-reticulum-retention sequences

Resident proteins of the endoplasmic reticulum lumen are continuously retrieved from an early Golgi compartment by a receptor-mediated mechanism. The sorting or retention sequence on the endoplasmic reticulum proteins is located at the C-terminus and was initially shown to be the tetrapeptide KDEL in mammalian cells and HDEL in Saccharomyces cerevisiae. The carboxylesterases are a large family of enzymes primarily localized to the lumen of the endoplasmic reticulum. Retention sequences in these proteins have been difficult to identify due to atypical and heterogeneous C-terminal sequences. Utilizing the polymerase chain reaction with degenerate primers, we have identified and characterized the C-termini of four members of the carboxylesterase family from rat liver. Three of the carboxylesterases sequences contained C-terminal sequences (HVEL, HNEL or HTEL) resembling the yeast sorting signal which were reported to be non-functional in mammalian cells. A fourth carboxylesterase contained a distinct C-terminal sequence, TEHT. A full-length esterase cDNA clone, terminating in the sequence HVEL, was isolated and was used to assess the retention capabilities of the various esterase C-terminal sequences. This esterase was retained in COS-1 cells, but was secreted when its C-terminal tetrapeptide, HVEL, was deleted. Addition of C-terminal sequences containing HNEL and HTEL resulted in efficient retention. However, the C-terminal sequence containing TEHT was not a functional retention signal. Both HDEL, the authentic yeast retention signal, and KDEL were efficient retention sequences for the esterase. These studies show that some members of the rat liver carboxylesterase family contain novel C-terminal retention sequences that resemble the yeast signal. At least one member of the family does not contain a C-terminal retention signal and probably represents a secretory form.

Isolation and characterization of arginine ester hydrolase from Heloderma horridum (beaded lizard) venom

1. An arginine ester hydrolase was isolated from Heloderma horridum (beaded lizard) venom by Sephadex G-75, DEAE-Sephacel and Q-Sepharose column chromatography, resulting in 5.4 mg of purified enzyme from 320.0 mg of crude venom. 2. The enzyme was shown to be homogeneous by both SDS and non-SDS disc electrophoresis on polyacrylamide gel at pH 8.3. 3. The enzyme possesses arginine ester hydrolase and transglutaminase-like activities, but did not exhibit clotting activity. 4. Molecular weight was determined to be ca 29 kDa, with an isoelectric point of 4.4. 5. The enzyme was stable to heat treatment (95 degrees C, 10 min) and to pH changes over the range 2-11. 6. The arginine ester hydrolase was inactivated by diisopropylfluorophosphate (DFP), beta-mercaptoethanol and N-bromosuccinimide, suggesting that serine, disulfide bonds and tryptophan are involved in enzymatic activity. 7. Amino terminal sequences were determined and appear to be similar to porcine pancreatic kallikrein.

Fusarium solani cutinase is a lipolytic enzyme with a catalytic serine accessible to solvent

Lipases belong to a class of esterases whose activity on triglycerides is greatly enhanced at lipid-water interfaces. This phenomenon, called interfacial activation, has a structural explanation: a hydrophobic lid, which at rest covers the catalytic site, is displaced on substrate or inhibitor binding and probably interacts with the lipid matrix. Fusarium solani pisi cutinase belongs to a group of homologous enzymes of relative molecular mass 22-25K (ref. 7) capable of degrading cutin, the insoluble lipid-polyester matrix covering the surface of plants, and hydrolysing triglycerides. Cutinases differ from classical lipases in that they do not exhibit interfacial activation; they are active on soluble as well as on emulsified triglycerides. Cutinases therefore establish a bridge between esterases and lipases. We report here the three-dimensional structure of a recombinant cutinase from F. solani pisi, expressed in Escherichia coli. Cutinase is an alpha-beta protein; the active site is composed of the triad Ser 120, His 188 and Asp 175. Unlike other lipases, the catalytic serine is not buried under surface loops, but is accessible to solvent. This could explain why cutinase does not display interfacial activation.

The alpha/beta hydrolase fold

We have identified a new protein fold--the alpha/beta hydrolase fold--that is common to several hydrolytic enzymes of widely differing phylogenetic origin and catalytic function. The core of each enzyme is similar: an alpha/beta sheet, not barrel, of eight beta-sheets connected by alpha-helices. These enzymes have diverged from a common ancestor so as to preserve the arrangement of the catalytic residues, not the binding site. They all have a catalytic triad, the elements of which are borne on loops which are the best-conserved structural features in the fold. Only the histidine in the nucleophile-histidine-acid catalytic triad is completely conserved, with the nucleophile and acid loops accommodating more than one type of amino acid. The unique topological and sequence arrangement of the triad residues produces a catalytic triad which is, in a sense, a mirror-image of the serine protease catalytic triad. There are now four groups of enzymes which contain catalytic triads and which are related by convergent evolution towards a stable, useful active site: the eukaryotic serine proteases, the cysteine proteases, subtilisins and the alpha/beta hydrolase fold enzymes.

Evidence that the methylesterase of bacterial chemotaxis may be a serine hydrolase

CheB, the methylesterase of chemotactic bacteria, catalyzes the hydrolysis of glutamyl-methyl esters in bacterial chemoreceptor proteins. The two cysteines predicted by the amino acid sequence of CheB were replaced by alanine residues. The resulting mutants, Cys207-Ala, Cys309-Ala and a double cysteine mutant Cys207-Ala/Cys309-Ala, retained methylesterase activity, indicating that sulfhydryls are not crucial for CheB mediated catalysis. A homology search revealed a conserved serine active-site region between residues 162 and 166 which is homologous to the active-site region of acetylcholine esterases, suggesting that Ser164 of CheB is the active-site nucleophile. Oligonucleotide-directed mutagenesis was used to change the serine to a cysteine. This Ser164-Cys mutant had less than 2% of the wild-type activity. Unlike the serine proteinases which utilize a 'catalytic triad' mechanism, CheB does not have the conserved histidine and aspartic acid residues located in positions N-terminal to the active-site serine. In addition, CheB is not labeled with di-isopropylfluorophosphate, a potent inhibitor of other serine hydrolases. A novel mechanism is proposed for CheB involving substrate-assisted catalysis to account for these apparent anomalies.

The use of three ferguson-plot-based calculation methods to determine the molecular mass of proteins as illustrated by molecular mass assessment of rat-plasma carboxylesterases ES-1, ES-2, and ES-14

The molecular masses of three rat-plasma carboxylesterases (ES-1, ES-2, and ES-14) were estimated by transverse-gradient polyacrylamide gel electrophoresis and subsequent application of Ferguson-plot-based calculation methods. Two electrophoretic buffer systems were used and the data subjected to either weighted or unweighted regression analysis. The Tris-boric acid buffer system produced significantly higher retardation coefficients than the Tris-glycine system. Molecular mass estimates were significantly higher with the Tris-glycine buffer system. Unweighted instead of weighted analysis produced significantly higher molecular mass estimates. Molecular mass estimates also depended on the calculation method, that is, the choice of calibration relationship with molecular size as a function of retardation coefficient. Three commonly used calibration relationships were compared. On the basis of their accuracy, both the weighted log[retardation coefficient] versus log[molecular mass] plot and the square root of retardation coefficient versus molecular radius were found suitable, provided that the Tris-boric acid buffer was used for electrophoresis. Using the former calibration relationship, the molecular masses of rat-plasma ES-1, ES-2, and ES-14 were 55.5, 61.1, and 65.3 kDa, respectively.

Detection and separation of some arginine amidases including tissue kallikrein from human seminal plasma

A plasminogen/plasmin like substance (AHSAA-1), with affinity to lysine column was separated from DEAE-cellulose adsorbed human seminal plasma. Two forms of acidic arginine amidase with different affinities to LBTI (AHSAA-2) and aprotinin columns (AHSAA-3) were separated from the DEAE-cellulose adsorbed preparation and AHSAA-3 was identified as tissue kallikrein. Two basic arginine amidase preparations having affinity to LBTI (BHSAA-1) and aprotinin column were also separated from the CM-cellulose adsorbed human seminal plasma. Three basic arginine amidases with different molecular mass (BHSAA-2 to 4) were separated by Cellulofine GCL-2000 gel filtration from aprotinin adsorbed material and some of their properties were examined.

Characterization and functional expression of a cDNA encoding egasyn (esterase-22): the endoplasmic reticulum-targeting protein of beta-glucuronidase

Egasyn (esterase-22), a member of the nonspecific carboxylesterase multigene family (E.C. 3.1.1.1), is the endoplasmic reticulum (ER)-targeting protein of beta-glucuronidase. We utilized the polymerase chain reaction (PCR) in the eventual isolation of murine egasyn cDNAs. PCR primers were based upon: (1) partial amino acid sequences derived from egasyn peptides and (2) a conserved active site region shared by carboxylesterases. The amino acid sequence deduced from the PCR product matched that obtained from egasyn protein. This product was utilized as a probe to screen a cDNA library. Two cDNAs whose composite sequence encoded an open reading frame of 562 amino acids were isolated. A message size of 1700-2000 bp was revealed by RNA blot hybridization analysis. S1 nuclease protection analyses detected mRNA in liver, kidney, lung, and submandibular gland, but not in spleen, brain, and testes. Genetic mapping confirmed the location of an egasyn cDNA fragment in cluster 1 of the esterase region on chromosome 8. Transfection of COS cells with the 2022-bp cDNA resulted in the expression of esterase activity, which comigrated on native gels with liver esterase-22. The features of the deduced amino acid sequence of the egasyn cDNA are compared with previously characterized carboxylesterases and with other lumenal ER proteins.

Basic arginine esterase from human seminal plasma: purification and some properties

Basic arginine esterase (amidase) with a specific activity of 3.2 mumol N-alpha-tosyl-L-arginine methyl ester (Tos-Arg-Me) esterolysis per A280 was purified about 230-fold from a CM-cellulose absorbed preparation of human seminal plasma. The purified enzyme was a single band with an apparent molecular weight of 3.4-4.1 x 10(4). The amidolytic activity of this enzyme was suppressed by aprotinin, soybean trypsin inhibitor (SBTI), leupeptin, and antipain, while alpha 1-antitrypsin, ovomucoid trypsin inhibitor (OTI), EDTA, and chymostatin had no or weak effect. This enzyme hydrolyzed synthetic basic amino acid derivatives and N-alpha-tosyl-glycyl-L-prolyl-arginine-p-nitroanilide (Tos-Gly-Pro-Arg-pNA) and N-alpha-tert-butyloxycarbonyl-L-leucyl-L-prolyl-L-arginine-p-nitroanilid e (Boc-Leu-Pro-Arg-pNA) were the best substrates. The enzymatic characteristics of present enzyme were clearly different from tissue kallikrein, acrosin, and seminin in human semen.

Extracellular poly(3-hydroxybutyrate) depolymerase from Penicillium funiculosum: general characteristics and active site studies

An extracellular poly(3-hydroxybutyrate) (PHB) depolymerase has been isolated from Penicillium funiculosum cultural medium by a single hydrophobic column chromatography. The enzyme is a glycoprotein composed of a single polypeptide chain with a molecular mass of about 37,000 Da as analyzed by denatured sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by native gel filtration on Sephadex G-100. Its optimum activity occurs at pH 6.0. It has an isoelectric point of 5.8 and has a Km for PHB (average molecular weight = 45,000 Da) of 0.17 mg/ml. Various nonionic detergents competitively inhibit the enzyme with Ki values of 0.56 and 0.014% for Tween 80 and Triton X-100, respectively. The enzyme is extremely sensitive to diisopropyl fluorophosphate, mercuric ion, and dithiothreitol (DTT). However, sulfhydryl reagents have little or no effect on its activity. The inactivation by mercuric ion and DTT is reversible by mercaptoethanol and hydrogen peroxide, respectively. These data suggest that the enzyme may be a serine esterase and may contain an important disulfide bond. The enzyme is also inactivated by diazoacetyl and epoxide compounds at low pH, which can be prevented by PHB, indicating the presence of a critical carboxyl group at the active site. These characteristics of the enzyme are compared to other extracellular polymerases isolated from bacterial culture media.

Isolation and characterization of p-coumaroyl esterase from the anaerobic fungus Neocallimastix strain MC-2

An extracellular p-coumaroyl esterase produced by the anaerobic fungus Neocallimastix strain MC-2 released p-coumaroyl groups from 0-[5-0-((E)-p-coumaroyl)-alpha-L-arabinofuranosyl]-(1----3)-0-beta -D-xylopyranosyl-(1----4)-D-xylopyranose (PAXX). The esterase was purified 121-fold from culture medium in successive steps involving ultrafiltration column chromatography on S-sepharose and hydroxylapatite, isoelectric focusing, and gel filtration. The native enzyme had an apparent mass of 11 kDa under nondenaturing conditions and a mass of 5.8 kDa under denaturing conditions, suggesting that the enzyme may exist as a dimer. The isoelectric point was 4.7, and the pH optimum was 7.2. The purified esterase had 100 times more activity towards PAXX than towards the analogous feruloyl ester (FAXX). The apparent Km and Vmax of the purified p-coumaroyl esterase for PAXX at pH 7.2 and 40 degrees C were 19.4 microM and 5.1 microM min(-1), respectively. p-Coumaroyl tetrasaccharides isolated from plant cell walls were hydrolyzed at rates similar to that for PAXX, whereas a dimer of PAXX was hydrolyzed at a rate 20-fold lower, yielding 4,4'-dihydroxy-alpha-truxillic acid as an end product. Ethyl and methyl p-coumarates were hydrolyzed at very slow rates, if at all. The purified esterase released p-coumaroyl groups from finely, but not coarsely, ground plant cell walls, and this activity was enhanced by the addition of xylanase and other cell wall-degrading enzymes.

Association of carboxylesterase B electrophoretic pattern with presence and expression of urovirulence factor determinants and antimicrobial resistance among strains of Escherichia coli that cause urosepsis

We determined the carboxylesterase B electrophoretic profiles of 74 blood isolates of Escherichia coli from patients with urosepsis. Most strains (64%) exhibited the B2 electrophoretic pattern. P fimbrial and hemolysin genetic determinants were present and expressed significantly more often among strains with the B2 than with the B1 electrophoretic pattern. In contrast, aerobactin determinants were significantly more prevalent and more commonly expressed among the B1 strains; this difference was attributable to the presence of plasmid-encoded aerobactin in one-third of the B1 strains (P = 0.02, B1 versus B2). The prevalence and extent of antimicrobial resistance was significantly greater among the B1 strains, and the B1 electrophoretic pattern was more often found in isolates from patients with urinary tract abnormalities. We conclude that the carboxylesterase B electrophoretic pattern differentiates two groups of E. coli isolates from patients with urosepsis: strains with the B1 electrophoretic pattern are associated with urologically impaired hosts, characteristically lack P fimbrial and hemolysin determinants, and often carry a plasmid-encoded aerobactin system (possibly on multiple antimicrobial resistance plasmids), whereas B2 strains more commonly invade noncompromised hosts, express P fimbriae and hemolysin, carry chromosomal aerobactin determinants, and lack antimicrobial resistance.

Specificity of the sex-influenced esterase (ES-SI) isozyme in rat liver

A carboxylesterase which shares common antigenicity with sex-influenced esterase (ES-SI) was found in both the male and the female liver of the rat but not in the following tissues: erythrocyte, heart, kidney, lung, spleen, small intestine, testis, thymus, and lymph node. Subcellular fractionation showed the esterase localizes in the microsome-rich fraction. The strain distribution of the presence or absence of the esterase in inbred rats was identical to that of ES-SI, although in adult males a considerable amount of the esterase exists, unlike ES-SI. The esterase had a higher isoelectric point than ES-SI but after neuraminidase treatment the difference disappeared, suggesting that the esterase has a sialic acid moiety. Because this esterase has different properties from those previously reported, it is proposed that it is designated liver-ES-SI. The common antigenicity and similar strain distribution between ES-SI and liver-ES-SI suggest that liver-ES-SI is a precursor molecule of ES-SI and therefore the two esterases are products of a single gene.

CPT-11 converting enzyme from rat serum: purification and some properties

A rat serum enzyme that catalyzes the conversion of a pro-drug, 7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin (CPT-11), to an anticancer drug, 7-ethyl-10-hydroxycamptothecin (SN-38), was purified and its properties were characterized. The enzyme was purified by column chromatography on diethylaminoethyl Toyopearl 650M, QAE-Sephadex, Sephadex G-150, Con A-Sepharose and high performance liquid chromatography with an ion-exchanger column. It was most active at pH 7.5 and was stable at pH 4-9 for 1 h at 30 degrees C. The molecular weight was estimated to be 60 and 57 kDa by gel filtration and sodium dodecylsulfate-polyacrylamide gel electrophoresis methods, respectively, and the isoelectric point was 4.6, as determined by isoelectric focusing. The Km value for CPT-11 was 0.28 microM. This enzyme was inhibited by diisopropyl phosphorofluoridate (DFP) and phenylmethanesulfonyl fluoride (PMSF) but insensitive to eserine, p-chloromercuribenzoate (PCMB) and ethylenediaminetetraacetate (EDTA). The enzyme also hydrolyzed p-nitrophenylacetate (p-NPA), a commonly used substrate for esterases, but was not active toward acetylcholine, suggesting that the enzyme is a carboxylesterase[EC 3.1.1.1]. During the hydrolyses of CPT-11 and p-NPA, an initial burst phenomenon similar to that found in the alpha-chymotrypsin-catalyzed hydrolysis of p-NPA was observed. Kinetic analysis revealed that the deacylation of the enzyme is the rate-limiting step in substrate hydrolysis. This enzyme was found to also split other ester derivatives of SN-38 besides CPT-11.

Thiol protease-like active site found in the enzyme dienelactone hydrolase: localization using biochemical, genetic, and structural tools

The active site of dienelactone hydrolase (DLH), a microbial enzyme of the beta-ketoadipate pathway, has been conclusively located using a combination of crystallographic, biochemical, and genetic techniques. DLH hydrolyzes a dienelactone to maleylacetate and has esterase activity on p-nitrophenyl acetate and trans-cinnamoyl imidazole. The identification of Cys-123 as containing the essential thiol confirms the localization of the active site as suggested by the crystal structure of DLH, and disproves an earlier hypothesis regarding its location. Two mutant proteins have been engineered in which Cys-123 has been converted to a serine (C123S DLH) and an alanine (C123A DLH), respectively. C123S DLH (Km = 9900 +/- 2300 microM; Vmax = 4.4 +/- 0.8 mumol/min-mg) displays burst kinetics with p-nitrophenyl acetate and is 10% as active as DLH (Km = 170 +/- 7 microM; Vmax = 21.1 +/- 0.4 mumol/min-mg). C123A DLH is inactive. The structures of DLH, C123S DLH, and C123A DLH have been refined at 1.8, 2.2, and 2.0 A, respectively. Comparison of the structures of these proteins demonstrates that the only differences between them are centered at residue 123. The structures of the active sites of DLH, papain, and subtilisin are similar and are suggestive of the three enzymes having evolved convergently to similar active sites with similar enzymic mechanisms.

Cytochemical and immunocytochemical characterization of Yoshida ascites sarcoma cells

Some cytochemical and immunocytochemical investigations were carried out on actively growing Yoshida ascites sarcoma cells. These cells displayed an intense granular alpha-naphthylacetate esterase (ANAE) staining while the alpha-naphthylbutyrate esterase (ANBE) reaction was in part fluoride-sensitive and marked particularly in the large-size malignant cells. Acid phosphatase as well as peroxidase activities were not detected. The lack of immunoreactive lysozyme and alpha 1-antitrypsin suggested a poor differentiation of the above-mentioned tumor cells, but fibronectin and S-100 protein where highly expressed, as in tumors arising from the mononuclear phagocyte system.

Molecular cloning and sequencing of a pectinesterase gene from Pseudomonas solanacearum

Two pectinesterase-positive Escherichia coli clones, differing in expression levels, were isolated from a genomic library of Pseudomonas solanacearum. Both clones contained a common DNA fragment which included the pectinesterase-encoding region. The different expression levels found with the two clones could be ascribed to different positioning of the pectinesterase gene with respect to a vector promoter. Restriction analysis, subcloning, and further exonuclease deletion mapping revealed that the genetic information for pectinesterase was located within a 1.3 kb fragment. A protein of 41 to 42 kDa was expressed from this fragment. Nucleotide sequence analysis of the respective region disclosed an open reading frame of 1188 bp. The deduced polypeptide had a calculated molecular mass of 41,004 Da, which is consistent with the determined size of the pectinesterase protein. The predicted amino acid sequence showed significant homology to pectinesterases from Erwinia chrysanthemi and tomato. In cultures of E. coli clones up to 30% of total pectinesterase activity was transported into the medium. However, no significant pectinesterase activity could be detected in the periplasm.

Characterization of affinity-purified juvenile hormone esterase from the plasma of the tobacco hornworm, Manduca sexta

Juvenile hormone (JH) esterase found primarily in the hemolymph and tissues of insects is a low abundance protein involved in the ester hydrolysis of insect juvenile hormones, JHs. The enzyme was purified from the larval plasma of wild-type Manduca sexta using an affinity column prepared by binding the ligand, 3-[(4'-mercapto)butylthio]-1,1,1-trifluoropropan-2-one (MBTFP), to epoxy-activated Sepharose. The purification was greater than 700-fold with a 72% recovery, and the purified enzyme appeared as a single protein on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoelectrophoresis, reverse phase high performance liquid chromatography, and amino acid sequence analysis. The molecular weight was 66,000. The plasma JH esterase in wild-type, black, and white strains of M. sexta was similar when analyzed by immunotitration, wide range (pH 3.5-9.0) isoelectric focusing, and inhibition with MBTFP and 3-octylthio-1,1,1-trifluoropropan-2-one (OTFP). Inhibition studies revealed a sensitive and insensitive form (I50 = 10(-9) and 10(-6) M, respectively) in these three biotypes. Narrow range isoelectric focusing (pH 4.0-7.0) indicated the presence of two major isoelectric forms with pI values of 6.0 and 5.5, but their inhibition kinetics with OTFP and O,O-diisopropyl phosphorofluoridate were identical.

Tomato and Aspergillus niger pectinesterases. Correlation of differences in existing reports: large species variations

Existing reports on the enzyme tomato pectinesterase differ in alignments of two internal segments and in many single-residue replacements. The alignment from cDNA data, with a 317-residue mature protein, is correct, but protein analyses also show at least 18 single-residue replacements, suggesting the presence of many native or (less likely) cloning-derived microheterogeneities. Purification of Aspergillus niger pectinesterase and N-terminal sequence analysis of this enzyme reveal a different structure and indicate an extensive protein divergence.

Human monocyte carboxylesterase. Purification and kinetics

Human peripheral blood monocytes were isolated by density gradient centrifugation and purified by counterflow centrifugation elutriation. Membrane-localized carboxylesterase (CBE) was extracted with nonionic detergent (Triton X-100) and purified by ion exchange (DEAE-cellulose), gel filtration (Sephacryl S-300), hydroxylapatite column, and high performance liquid chromatography. The purified enzyme migrated on 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis as a single protein band with a molecular weight of 60,000. Under nondenaturing conditions, monocyte CBE formed a trimer and eluted from a gel filtration column as a protein with an approximate molecular weight of 200,000. Electrophoretic patterns of the enzyme on polyacrylamide gels run a neutral pH did not vary during enzyme purification. At least four major isoenzymes of human monocyte CBE were observed with isoelectric points between 7.5 and 7.8. Pure human monocyte CBE hydrolyzed short chain alpha-naphthyl, o-nitrophenyl, and p-nitrophenyl esters. Amide esters and thioesters were not hydrolyzed by the enzyme. Short chain alcohols activated the enzyme and organophosphorus compounds, diphenyl carbonate, sodium fluoride, and phenylmethylsulfonyl fluoride inhibited the enzyme. EDTA and sulfhydryl reagents had no effect on enzyme activity. The amino acid content of the enzyme was consistent with other CBEs. Inhibitors reacted either with the active or effector site of the enzyme. Purified enzyme now permits the characterization of CBE structure and regulation.

Crystallization and preliminary X-ray study of a recombinant cutinase from Fusarium solani pisi

Recombinant cutinase from Fusarium solani pisi is expressed and excreted with very high yields in Escherichia coli cultures. Cutinase was crystallized at 20 degrees C using the vapour diffusion technique, with polyethylene glycol 6000 as precipitant. Best crystals were obtained at pH 7.0 with polyethylene glycol 6000 as precipitant. Best crystals were obtained at pH 7.0 with polyethylene glycol at 15 to 20%. They are monoclinic, with space group P2(1) and cell dimensions a = 35.1 A, b = 67.4 A, c = 37.05 A and beta = 94.0 degrees; they diffract beyond 1.5 A resolution. The asymmetric unit contains one molecule of 22,000 Da (Vm = 1.98 A3/Da; 38% water).