An esterase from Escherichia coli with a sequence similarity to hormone-sensitive lipase

Biocide-Induced Emergence of Antibiotic Resistance in Escherichia coli

Biocide use is essential and ubiquitous, exposing microbes to sub-inhibitory concentrations of antiseptics, disinfectants, and preservatives. This can lead to the emergence of biocide resistance, and more importantly, potential cross-resistance to antibiotics, although the degree, frequency, and mechanisms that give rise to this phenomenon are still unclear. Here, we systematically performed adaptive laboratory evolution of the gut bacteria Escherichia coli in the presence of sub-inhibitory, constant concentrations of ten widespread biocides. Our results show that 17 out of 40 evolved strains (43%) also decreased the susceptibility to medically relevant antibiotics. Through whole-genome sequencing, we identified mutations related to multidrug efflux proteins (mdfA and acrR), porins (envZ and ompR), and RNA polymerase (rpoA and rpoBC), as mechanisms behind the resulting (cross)resistance. We also report an association of several genes (yeaW, pyrE, yqhC, aes, pgpA, and yeeP-isrC) and specific mutations that induce cross-resistance, verified through mutation repairs. A greater capacity for biofilm formation with respect to the parent strain was also a common feature in 11 out of 17 (65%) cross-resistant strains. Evolution in the biocides chlorophene, benzalkonium chloride, glutaraldehyde, and chlorhexidine had the most impact in antibiotic susceptibility, while hydrogen peroxide and povidone-iodine the least. No cross-resistance to antibiotics was observed for isopropanol, ethanol, sodium hypochlorite, and peracetic acid. This work reinforces the link between exposure to biocides and the potential for cross-resistance to antibiotics, presents evidence on the underlying mechanisms of action, and provides a prioritized list of biocides that are of greater concern for public safety from the perspective of antibiotic resistance.

SIGNIFICANCE STATEMENT

Bacterial resistance and decreased susceptibility to antimicrobials is of utmost concern. There is evidence that improper biocide (antiseptic and disinfectant) use and discard may select for bacteria cross-resistant to antibiotics. Understanding the cross-resistance emergence and the risks associated with each of those chemicals is relevant for proper applications and recommendations. Our work establishes that not all biocides are equal when it comes to their risk of inducing antibiotic resistance; it provides evidence on the mechanisms of cross-resistance and a risk assessment of the biocides concerning antibiotic resistance under residual sub-inhibitory concentrations.

Development and application of a highly efficient CRISPR-Cas9 system for genome engineering in Bacillus megaterium

Bacillus megaterium has become increasingly important for the biotechnological production of valuable compounds of industrial and pharmaceutical importance. Despite recent advances in rational strain design of B. megaterium, these studies have been largely impaired by the lack of molecular tools that are not state-of-the-art for comprehensive genome engineering approaches. In the current work, we describe the adaptation of the CRISPR-Cas9 vector pJOE8999 to enable efficient genome editing in B. megaterium. Crucial modifications comprise the exchange of promoter elements and associated ribosomal binding sites as well as the implementation of a 5-fluorouracil based counterselection system to facilitate proper plasmid curing. In addition, the functionality and performance of the new CRISPR-Cas9 vector pMOE was successfully evaluated by chromosomal disruption studies of the endogenous β-galactosidase gene (BMD_2126) and demonstrated an outstanding efficiency of 100 % based on combinatorial pheno- and genotype analyses. Furthermore, pMOE was applied for the genomic deletion of a steroid esterase gene (BMD_2256) that was identified among several other candidates as the gene encoding the esterase, which prevented accumulation of pharmaceutically important glucocorticoid esters. Recombinant expression of the bacterial chloramphenicol acetyltransferase 1 gene (cat1) in the resulting esterase deficient B. megaterium strain ultimately yielded C21-acetylated as well as novel C21-esterified derivates of cortisone.

Exploration of Acetylation as a Base-Labile Protecting Group in Escherichia coli for an Indigo Precursor

Biochemical protecting groups are observed in natural metabolic pathways to control reactivity and properties of chemical intermediates; similarly, they hold promise as a tool for metabolic engineers to achieve the same goals. Protecting groups come with costs: lower yields from carbon, metabolic load to the production host, deprotection catalyst costs and kinetics limitations, and wastewater treatment of the group. Compared to glycosyl biochemical protection, such as glucosyl groups, acetylation can mitigate each of these costs. As an example application where these benefits could be valuable, we explored acetylation protection of indoxyl, the reactive precursor to the clothing dye, indigo. First, we demonstrated denim dyeing with chemically sourced indoxyl acetate by deprotection with base, showing results comparable to industry-standard denim dyeing. Second, we modified an Escherichia coli production host for improved indoxyl acetate stability by the knockout of 14 endogenous hydrolases. Cumulatively, these knockouts yielded a 67% reduction in the indoxyl acetate hydrolysis rate from 0.22 mmol/g DCW/h to 0.07 mmol/g DCW/h. To biosynthesize indoxyl acetate, we identified three promiscuous acetyltransferases which acetylate indoxyl in vivo. Indoxyl acetate titer, while low, was improved 50%, from 43 μM to 67 μM, in the hydrolase knockout strain compared to wild-type E. coli. Unfortunately, low millimolar concentrations of indoxyl acetate proved to be toxic to the E. coli production host; however, the principle of acetylation as a readily cleavable and low impact biochemical protecting group and the engineered hydrolase knockout production host should prove useful for other metabolic products.

Main Structural Targets for Engineering Lipase Substrate Specificity

Microbial lipases represent one of the most important groups of biotechnological biocatalysts. However, the high-level production of lipases requires an understanding of the molecular mechanisms of gene expression, folding, and secretion processes. Stable, selective, and productive lipase is essential for modern chemical industries, as most lipases cannot work in different process conditions. However, the screening and isolation of a new lipase with desired and specific properties would be time consuming, and costly, so researchers typically modify an available lipase with a certain potential for minimizing cost. Improving enzyme properties is associated with altering the enzymatic structure by changing one or several amino acids in the protein sequence. This review detailed the main sources, classification, structural properties, and mutagenic approaches, such as rational design (site direct mutagenesis, iterative saturation mutagenesis) and direct evolution (error prone PCR, DNA shuffling), for achieving modification goals. Here, both techniques were reviewed, with different results for lipase engineering, with a particular focus on improving or changing lipase specificity. Changing the amino acid sequences of the binding pocket or lid region of the lipase led to remarkable enzyme substrate specificity and enantioselectivity improvement. Site-directed mutagenesis is one of the appropriate methods to alter the enzyme sequence, as compared to random mutagenesis, such as error-prone PCR. This contribution has summarized and evaluated several experimental studies on modifying the substrate specificity of lipases.

Elevating 4-hydroxycoumarin production through alleviating thioesterase-mediated salicoyl-CoA degradation

Acyl-CoAs are essential intermediates in the biosynthetic pathways of a number of industrially and pharmaceutically important molecules. When these pathways are reconstituted in a heterologous microbial host for metabolic engineering purposes, the acyl-CoAs may be subject to undesirable hydrolysis by the host's native thioesterases, resulting in a waste of cellular energy and decreased intermediate availability, thus impairing bioconversion efficiency. 4-hydroxycoumarin (4HC) is a direct synthetic precursor to the commonly used oral anticoagulants (e.g. warfarin) and rodenticides. In our previous study, we have established an artificial pathway for 4HC biosynthesis in Escherichia coli, which involves the thioester intermediate salicoyl-CoA. Here, we utilized the 4HC pathway as a demonstration to examine the negative effect of salicoyl-CoA degradaton, identify and inactivate the responsible thioesterase, and eventually improve the 4HC production. We screened a total of 16 E. coli thioesterases and tested their hydrolytic activity towards salicoyl-CoA in vitro. Among all the tested candidate enzymes, YdiI was found to be the dominant contributor to the salicoyl-CoA degradation in E. coli. Remarkably, the ydiI knockout strain carrying the 4HC pathway exhibited an up to 300% increase in 4HC production. An optimized 4HC pathway construct introduced in the ydiI knockout strain led to the accumulation of 935mg/L of 4HC in shake flasks, which is about 1.5 folds higher than the wild-type strain. This study demonstrates a systematic strategy to alleviate the undesirable hydrolysis of thioester intermediates, allowing production enhancement for other biosynthetic pathways with similar issues.

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.

Identification of lipase encoding genes from Antarctic seawater bacteria using degenerate primers: expression of a cold-active lipase with high specific activity

Cold-active enzymes are valuable catalysts showing high activity at low and moderate temperatures and low thermostability. Among cold-active enzymes, lipases offer a great potential in detergent, cosmetic, biofuel and food or feed industries. In this paper we describe the identification of novel lipase coding genes and the expression of a lipase with high activity at low temperatures. The genomic DNA from Antarctic seawater bacteria showing lipolytic activity at 4°C was used to amplify five DNA fragments that partially encode novel lipases using specifically designed COnsensus-DEgenerate Hybrid Oligonucleotide Primers (CODEHOP). All the fragments were found to have a high identity with an α/β-hydrolase domain-containing protein identified by the sequencing of the complete genome of Shewanella frigidimarina NCIMB 400. The complete sequence of one of the lipase-coding gene fragments, lipE13, was obtained by genome walking. Considering that the other fragments had a high identity to the putative lipase from S. frigidimarina NCIMB 400, the complete lipase genes were amplified using oligonucleotide primers designed based on the 5' and 3' regions of the coding sequence of the related protein. This strategy allowed the amplification of 3 lipase-encoding genes of which one was expressed in the periplasm using the Escherichia coli BL21(DE3)/pET-22b(+) expression system. The recombinant protein was obtained with activity toward p-nitrophenyl caproate showing a high specific activity between 15 and 25°C.

Metal ion activated lipase from halotolerant Bacillus sp. VITL8 displays broader operational range

Lipase producing halo tolerant Bacillus sp. VITL8 was isolated from oil contaminated areas of Vellore. The identity of the organism was established by 16S rDNA sequence, in addition to the morphological and biochemical characterization. The purified enzyme (22kDa, 8680U/mg) exhibited optimal activity at pH 7.0 and 40°C and retained more than 50% of its activity in the NaCl concentration range of 0-3.0M, pH 6.0-10.0 and 10-60°C. Secondary structure analysis, using circular dichroism, revealed that the enzyme is composed of 38% α-helix and 29% β-turns. The lipase activity significantly increased in the presence of (1mM) Mn(2+) (139%), Ca(2+) (134%) and Mg(2+) (130%). Organic solvents such as butanol and acetonitrile (25%, v/v) enhanced the activity whereas DMSO (25% v/v) retained the activity. The Km of enzyme-p-Nitrophenyl palmitate complex was determined to be 191μM with a Vmax of 68μM/mg/min. Though halotolerant Bacillus sp. has been explored for hydrocarbon degradation, to our knowledge this is the first report on the lipase activity of the isolate. The characteristics of the enzyme presented in this report, imply broader operational range of the enzyme and therefore could be suitable for many of the industrial chemical processes.

Optimized design and synthesis of a cell-permeable biarsenical cyanine probe for imaging tagged cytosolic bacterial proteins

To optimize cellular delivery and specific labeling of tagged cytosolic proteins by biarsenical fluorescent probes built around a cyanine dye (Cy3) scaffold, we have systematically varied the polarity of the N-alkyl chain (i.e., 4-5 methylene groups appended by a sulfonate or methoxy ester moiety) and arsenic capping reagent (ethanedithiol versus benzenedithiol). Optimal live-cell labeling and visualization of tagged cytosolic proteins is reported using an ethanedithiol capping reagent with the uncharged methoxy ester functionalized N-alkyl chains. These measurements demonstrate the general utility of this new class of photostable and highly fluorescent biarsenical probes based on the cyanine dye scaffold for in vivo labeling of tagged cellular proteins for live cell imaging measurements of protein dynamics.

Link between intraphagosomal biotin and rapid phagosomal escape in Francisella

Cytosolic bacterial pathogens require extensive metabolic adaptations within the host to replicate intracellularly and cause disease. In phagocytic cells such as macrophages, these pathogens must respond rapidly to nutrient limitation within the harsh environment of the phagosome. Many cytosolic pathogens escape the phagosome quickly (15-60 min) and thereby subvert this host defense, reaching the cytosol where they can replicate. Although a great deal of research has focused on strategies used by bacteria to resist antimicrobial phagosomal defenses and transiently pass through this compartment, the metabolic requirements of bacteria in the phagosome are largely uncharacterized. We previously identified a Francisella protein, FTN_0818, as being essential for intracellular replication and involved in virulence in vivo. We now show that FTN_0818 is involved in biotin biosynthesis and required for rapid escape from the Francisella-containing phagosome (FCP). Addition of biotin complemented the phagosomal escape defect of the FTN_0818 mutant, demonstrating that biotin is critical for promoting rapid escape during the short time that the bacteria are in the phagosome. Biotin also rescued the attenuation of the FTN_0818 mutant during infection in vitro and in vivo, highlighting the importance of this process. The key role of biotin in phagosomal escape implies biotin may be a limiting factor during infection. We demonstrate that a bacterial metabolite is required for phagosomal escape of an intracellular pathogen, providing insight into the link between bacterial metabolism and virulence, likely serving as a paradigm for other cytosolic pathogens.

Discovery of an Escherichia coli esterase with high activity and enantioselectivity toward 1,2-O-isopropylideneglycerol esters

Escherichia coli has been widely used as an expression host for the identification of desired biocatalysts through screening or selection assays. We have previously used E. coli in growth selection and screening assays for identification of Bacillus subtilis lipase variants (located in the periplasm) with improved activity and enantioselectivity toward 1,2-O-isopropylideneglycerol (IPG) esters. In the course of these studies, we discovered that E. coli itself exhibits significant cytoplasmic esterase activity toward IPG esters. In order to identify the enzyme (or enzymes) responsible for this esterase activity, we analyzed eight E. coli knockout strains, in which single esterase genes were deleted, for their ability to hydrolyze IPG butyrate. This approach led to the identification of esterase YbfF as the major E. coli enzyme responsible for the hydrolytic activity toward IPG esters. The gene coding for YbfF was cloned and overexpressed in E. coli, and the corresponding protein was purified and characterized for its biocatalytic performance. YbfF displays a high level of activity toward IPG butyrate and IPG caprylate and prefers the R-enantiomer of these substrates, producing the S-enantiomer of the IPG product with high enantiomeric excess (72 to 94% ee). The enantioselectivity of YbfF for IPG caprylate (E = 40) could be significantly enhanced when using dimethylformamide (DMF) or dimethyl sulfoxide (DMSO) as cosolvents in kinetic resolution experiments. The enzyme also shows high enantioselectivity toward 1-phenylethyl acetate (E ≥ 200), giving the chiral product (R)-1-phenylethanol with >99% ee. The high activity and enantioselectivity of YbfF make it an attractive enzyme for organic synthesis.

Identification of a new subfamily of salt-tolerant esterases from a metagenomic library of tidal flat sediment

To search for novel lipolytic enzymes, a metagenomic library was constructed from the tidal flat sediment of Ganghwa Island in South Korea. By functional screening using tributyrin agar plates, 3 clones were selected from among the 80,050 clones of the fosmid library. The sequence analysis revealed that those clones contained different open reading frames, which showed 50-57% amino acid identity with putative lipolytic enzymes in the database. Based on the phylogenetic analysis, they were identified to encode novel members, which form a distinct and new subfamily in the family IV of bacterial lipolytic enzymes. The consensus sequence, GT(S)SA(G)G, encompassing the active site serine of the enzymes was different from the GDSAG motif, conserved in the other subfamily. The genes were expressed in Escherichia coli and recombinant proteins were purified as active soluble forms. The enzymes showed the highest activity toward p-nitrophenyl valerate (C5) and exhibited optimum activities at mesophilic temperature ranges and slightly alkaline pH. In particular, the enzymes displayed salt tolerance with over 50% of the maximum activity remained in the presence of 3 M NaCl (or KCl). In this study, we demonstrated that the metagenomic approach using marine tidal flat sediment as a DNA source expanded the diversity of lipolytic enzyme-encoding genes.

Three-Dimensional Structure of Arabidopsis thaliana Lipase Predicted by Homology Modeling Method

Triacylglycerol lipases have been thoroughly characterized in mammals and microorganisms. By contrast, very little is known about plant lipases. In this investigation, a homology model of Arabidopsis thaliana lipase (NP_179126) was constructed using a human gastric lipase (PDB ID: 1HLG), as a template for model building. This model was then assessed for stereochemical quality and side chain environment. Natural substrates: tributyrin, trioctanoin and triolen were docked into the model to investigate ligand-substrate interaction.

A critical examination of Escherichia coli esterase activity

The ability of Escherichia coli to grow on a series of acetylated and glycosylated compounds has been investigated. It is surmised that E. coli maintains low levels of nonspecific esterase activity. This observation may have ramifications for previous reports that relied on nonspecific esterases from E. coli to genetically encode nonnatural amino acids. It had been reported that nonspecific esterases from E. coli deacetylate tri-acetyl O-linked glycosylated serine and threonine in vivo. The glycosylated amino acids were reported to have been genetically encoded into proteins in response to the amber stop codon. However, it is our contention that such amino acids are not utilized in this manner within E. coli. The current results report in vitro analysis of the original enzyme and an in vivo analysis of a glycosylated amino acid. It is concluded that the amber suppression method with nonnatural amino acids may require a caveat for use in certain instances.

Hexose/Pentose and Hexitol/Pentitol Metabolism

Escherichia coli and Salmonella enterica serovar Typhimurium exhibit a remarkable versatility in the usage of different sugars as the sole source of carbon and energy, reflecting their ability to make use of the digested meals of mammalia and of the ample offerings in the wild. Degradation of sugars starts with their energy-dependent uptake through the cytoplasmic membrane and is carried on further by specific enzymes in the cytoplasm, destined finally for degradation in central metabolic pathways. As variant as the different sugars are, the biochemical strategies to act on them are few. They include phosphorylation, keto-enol isomerization, oxido/reductions, and aldol cleavage. The catabolic repertoire for using carbohydrate sources is largely the same in E. coli and in serovar Typhimurium. Nonetheless, significant differences are found, even among the strains and substrains of each species. We have grouped the sugars to be discussed according to their first step in metabolism, which is their active transport, and follow their path to glycolysis, catalyzed by the sugar-specific enzymes. We will first discuss the phosphotransferase system (PTS) sugars, then the sugars transported by ATP-binding cassette (ABC) transporters, followed by those that are taken up via proton motive force (PMF)-dependent transporters. We have focused on the catabolism and pathway regulation of hexose and pentose monosaccharides as well as the corresponding sugar alcohols but have also included disaccharides and simple glycosides while excluding polysaccharide catabolism, except for maltodextrins.

New thermophilic and thermostable esterase with sequence similarity to the hormone-sensitive lipase family, cloned from a metagenomic library

A gene coding for a thermostable esterase was isolated by functional screening of Escherichia coli cells that had been transformed with fosmid environmental DNA libraries constructed with metagenomes from thermal environmental samples. The gene conferring esterase activity on E. coli grown on tributyrin agar was composed of 936 bp, corresponding to 311 amino acid residues with a molecular mass of 34 kDa. The enzyme showed significant amino acid similarity (64%) to the enzyme from a hyperthermophilic archaeon, Pyrobaculum calidifontis. An amino acid sequence comparison with other esterases and lipases revealed that the enzyme should be classified as a new member of the hormone-sensitive lipase family. The recombinant esterase that was overexpressed and purified from E. coli was active above 30 degrees C up to 95 degrees C and had a high thermal stability. It displayed a high degree of activity in a pH range of 5.5 to 7.5, with an optimal pH of approximately 6.0. The best substrate for the enzyme among the p-nitrophenyl esters (C(4) to C(16)) examined was p-nitrophenyl caproate (C(6)), and no lipolytic activity was observed with esters containing an acyl chain length of longer than 10 carbon atoms, indicating that the enzyme is an esterase and not a lipase.

Mutational analysis of the "regulatory module" of hormone-sensitive lipase

Hormone-sensitive lipase (HSL) is a rate-limiting enzyme in lipolysis that displays broad substrate specificity. HSL function is regulated by reversible phosphorylation that occurs within a 150 aa "regulatory module" of the protein. The current studies used mutational analysis to dissect the contribution of the "regulatory module" in HSL activity and substrate specificity. Deletion of the entire "regulatory module" or replacement of the "regulatory module" with the "lid" of lipoprotein lipase resulted in enzymatically inactive proteins. Deletion of sequentially longer stretches of the "regulatory module" resulted in a stepwise reduction in hydrolytic activity. Analysis of 7-19 amino acid deletional mutants that spanned the "regulatory module" showed that the N-terminal partial deletion mutants retained normal hydrolytic activity and activation by PKA. In contrast, the C-terminal partial deletion mutants displayed reduced hydrolytic activities, with preferential loss of activity against lipid-, as opposed to water-soluble, substrates. Single amino acid mutations of F650C, P651A, and F654D reduced activity against lipid-, but not water-soluble, substrates. The current results suggest that the length of the "regulatory module" and specific sequences within the C-terminal portion of the "regulatory module" of HSL (amino acids 644-683) are crucial for activity and appear to be responsible for determining lipase activity.

Denaturant-induced unfolding of the acetyl-esterase from Escherichia coli

The stability of acetyl-esterase, Aes, from Escherichia coli against the denaturing action of urea and guanidine hydrochloride, GuHCl, has been investigated by means of circular dichroism and fluorescence measurements. The urea-induced unfolding curves show a single inflection point at 6.2 M urea, whereas the GuHCl-induced curves show two inflection points at 1.4 and 3.1 M GuHCl. The unfolding process is reversible with both urea and GuHCl. These results, together with similar experimental data on the mutant form V20D-Aes, suggest the presence of two domains in the Aes structure, which unfold more or less independently depending on the denaturant used. This is also supported by a 3D model obtained by homology modeling using the structure of brefeldine as a template. The effect of NaCl on the urea-induced unfolding curves of the enzyme has also been investigated.

Mycoplasma hyopneumoniae p65 surface lipoprotein is a lipolytic enzyme with a preference for shorter-chain fatty acids

Mycoplasma hyopneumoniae is the most significant bacterial pathogen of the respiratory tract of swine. p65 is an immunodominant surface lipoprotein of M. hyopneumoniae that is specifically recognized during disease. Analysis of the translated amino acid sequence of the gene encoding p65 revealed similarity to the GDSL family of lipolytic enzymes. To examine the lipolytic activity of p65, the gene was cloned and expressed in Escherichia coli after truncation of the prokaryotic lipoprotein signal sequence and mutagenesis of the mycoplasma TGA tryptophan codons. After treatment with thrombin, the recombinant glutathione S-transferase (GST)-p65 protein yielded a 66-kDa fusion protein cleavage product corresponding in size to the mature p65 protein. The esterase activity of recombinant GST-p65 was indicated by the formation of a cleared zone on tributyrin agar plates and the hydrolysis of p-nitrophenyl esters of caproate (pNPC) and p-nitrophenyl esters of palmitate (pNPP). Lipase activity was indicated by the hydrolysis of the artificial triglyceride 1,2-O-dilauryl-rac-glycero-3-glutaric acid resorufin ester. Using pNPC and pNPP as substrates, recombinant GST-p65 had optimal activity between pHs 9.2 and 10.2 and at a temperature higher than 39 degrees C. Calcium ions did not increase the activity of recombinant GST-p65. Rabbit anti-p65 antibodies inhibited the activity of recombinant GST-p65 and also inhibited the growth of M. hyopneumoniae in vitro. Examination of the kinetic parameters of recombinant GST-p65 for the hydrolysis of pNPC and pNPP indicated a preference for the shorter fatty acid chain of pNPC. The physiological and/or pathogenic role of mycoplasma lipolytic enzymes has not been determined, but they are likely to play an important role in mycoplasmas' nutritional requirements for long-chain fatty acids and may reduce the function of lung surfactants in mycoplasma-induced respiratory diseases. This is the first report of the lipolytic activity of a lipid-modified surface immunogen of a mycoplasma.

Starch acetate microparticles for drug delivery into retinal pigment epithelium—in vitro study

Starch acetates are novel biodegradable polymers which undergo slower degradation and swelling than native starch. Retinal pigment epithelium (RPE) is an important target tissue in ocular treatment. The cellular uptake of starch acetate microparticles and degradation of starch acetate by cultured human RPE-cell line (D407) was examined. Calcein-containing starch acetate microparticles were prepared by a modified water-in-oil-in-water double-emulsion technique. The cellular uptake of the starch acetate microparticles was analysed using flow cytometry and confocal microscopy. Degradation of starch acetate films by the homogenate of lysed RPE cells was determined by gel permeation chromatography. The effect of the microparticles on RPE cell viability was determined by the MTT colorimetric assay. The mean diameter (D50%) of microparticles was 11 microm. During 3-h incubation in RPE-cell culture, 8.1 +/- 0.8% of D407 cells took up starch acetate microparticles. Confocal microscopy confirmed the internalisation of microparticles. Incubation of the starch acetate film in the RPE-cell homogenate considerably decreased the molecular weight of starch acetate in the film during 24 h. The viability of cultured RPE cells was at least 82% after 24-h incubation with the microparticles. The present results show that the starch acetate microparticles are taken up by the RPE cells and the polymer can be degraded by the enzymes in these cells. Starch acetate microparticles may be suitable for drug delivery to the RPE.

Drug release from starch-acetate microparticles and films with and without incorporated α-amylase

Acetylation of starch considerably decreases its swelling and enzymatic degradation. Thus, starch-acetate (SA) based delivery systems may be suitable for controlled drug delivery. The aim of the present study was to evaluate drug release from the SA microparticles (SA mps) and SA films. The average degree of acetyl substitution (DS) per glucose residue in the starch was either 1.9 (SA DS 1.9) or 2.6 (SA DS 2.6). Timolol (mw 332), calcein (mw 623) and bovine serum albumin (BSA, mw 68,000) were used as model drugs. A continuous timolol release from the both SA mps was observed in phosphate buffer solution (PBS) pH 7.4 (50-days incubation). The release of timolol was faster from the SA DS 1.9 mps than from the SA DS 2.6 mps. Calcein release from both SA mps was continuous in PBS pH 7.4 (5-days incubation). But, calcein release profile from the SA DS 2.6 film in PBS pH 7.4 showed discontinuities. However, the release of calcein from both SA films was continuous in human serum in vitro during the 7-day incubation, i.e. enzymes enhanced calcein release. Thus, alpha-amylase was incorporated into the SA films in order to enhance drug release from the films. However, the effects of incorporation of alpha-amylase on the model macromolecule (BSA) release from the SA films were modest. In conclusion, this study demonstrates the achievement of slow release of different molecular weight model drugs from the SA mps and films as compared to fast release from the native starch preparations. DS of SA, physicochemical properties of a drug and the presence of enzymes can all affect drug release profiles from SA based preparations.

Cold-active esterase from Psychrobacter sp. Ant300: gene cloning, characterization, and the effects of Gly→Pro substitution near the active site on its catalytic activity and stability

The gene encoding an esterase (PsyEst) of Psychrobacter sp. Ant300, a psychrophilic bacterium isolated from Antarctic soil, was cloned, sequenced, and expressed in Escherichia coli. PsyEst, which is a member of hormone-sensitive lipase (HSL) group of the lipase/esterase family, is a cold-active, themolabile enzyme with high catalytic activity at low temperatures (5-25 degrees C), low activation energy (e.g., 4.6 kcal/mol for hydrolysis of p-nitrophenyl butyrate), and a t(1/2) value of 16 min for thermal inactivation during incubation at 40 degrees C and pH 7.9. A three-dimensional structural model of PsyEst predicted that Gly(244) was located in the loop near the active site of PsyEst and that substitution of this amino-acid residue by proline should potentially rigidify the active-site environment of the enzyme. Thus, we introduced the Gly(244)-->Pro substitution into the enzyme. Stability studies showed that the t(1/2) value for thermal inactivation of the mutant during incubation at 40 degrees C and pH 7.9 was 11.6 h, which was significantly greater than that of the wild-type enzyme. The k(cat)/K(m) value of the mutant was lower for all substrates examined than the value of the wild type. Moreover, this amino-acid substitution caused a shift of the acyl-chain length specificity of the enzyme toward higher preference for short-chain fatty acid esters. All of these observations could be explained in terms of a decrease in active-site flexibility brought about by the mutation and were consistent with the hypothesis that cold activity and thermolability arise from local flexibility around the active site of the enzyme.

The crystal structure of CCG1/TAF(II)250-interacting factor B (CIB)

The general transcription initiation factor TFIID and its interactors play critical roles in regulating the transcription from both naked and chromatin DNA. We have isolated a novel TFIID interactor that we denoted as CCG1/TAF(II)250-interacting factor B (CIB). We show here that CIB activates transcription. To further understand the function of this protein, we determined its crystal structure at 2.2-Angstroms resolution. The tertiary structure of CIB reveals an alpha/beta-hydrolase fold that resembles structures in the prokaryotic alpha/beta-hydrolase family proteins. It is not similar in structure or primary sequence to any eukaryotic transcription or chromatin factors that have been reported to date. CIB possesses a conserved catalytic triad that is found in other alpha/beta-hydrolases, and our in vitro studies confirmed that it bears hydrolase activity. However, CIB differs from other alpha/beta-hydrolases in that it lacks a binding site excursion, which facilitates the substrate selectivity of the other alpha/beta-hydrolases. Further functional characterization of CIB based on its tertiary structure and through biochemical studies may provide novel insights into the mechanisms that regulate eukaryotic transcription.

Integrating structure, bioinformatics, and enzymology to discover function: BioH, a new carboxylesterase from Escherichia coli

Structural proteomics projects are generating three-dimensional structures of novel, uncharacterized proteins at an increasing rate. However, structure alone is often insufficient to deduce the specific biochemical function of a protein. Here we determined the function for a protein using a strategy that integrates structural and bioinformatics data with parallel experimental screening for enzymatic activity. BioH is involved in biotin biosynthesis in Escherichia coli and had no previously known biochemical function. The crystal structure of BioH was determined at 1.7 A resolution. An automated procedure was used to compare the structure of BioH with structural templates from a variety of different enzyme active sites. This screen identified a catalytic triad (Ser82, His235, and Asp207) with a configuration similar to that of the catalytic triad of hydrolases. Analysis of BioH with a panel of hydrolase assays revealed a carboxylesterase activity with a preference for short acyl chain substrates. The combined use of structural bioinformatics with experimental screens for detecting enzyme activity could greatly enhance the rate at which function is determined from structure.

Effect of trifluoroethanol on the conformational stability of a hyperthermophilic esterase: a CD study

The conformational stability of the hyperthermophilic esterase AFEST from Archeoglobus fulgidus against the denaturing action of 2,2,2-trifluoroethanol (TFE) has been investigated by means of circular dichroism (CD) measurements. At room temperature far-UV and near-UV CD spectra point out the occurrence of a co-operative transition from the native structure to a denatured state characterized by a high content of alpha-helix. The TFE concentration at half-completion of the transition proves to be 3.5 M (25% v v(-1)), by recording the molar ellipticity at both 222 and 276 nm. Thermal transition curves of AFEST in the absence and in the presence of TFE indicate a significant stability decrease on increasing the TFE concentration. The denaturation temperature is 99 degrees C for native AFEST, but becomes 85 degrees C at 1.4 M TFE (10% v v(-1)), and 56 degrees C at 2.8 M TFE (20% v v(-1)). It is also shown that, even though AFEST is very resistant to temperature, its resistance towards the denaturing action of TFE is similar to that of mesophilic proteins, including an esterase from Escherichia coli, AES. The proposal of a general mechanism for the TFE action on globular proteins leads to a reliable rationale of experimental data.

Structural and catalytic response to temperature and cosolvents of carboxylesterase EST1 from the extremely thermoacidophilic archaeon Sulfolobus solfataricus P1

The interactive effects of temperature and cosolvents on the kinetic and structural features of a carboxylesterase from the extremely thermoacidophilic archaeon Sulfolobus solfataricus P1 (Sso EST1) were examined. While dimethylformamide, acetonitrile, and dioxane were all found to be deleterious to enzyme function, dimethyl sulfoxide (DMSO) activated Sso EST1 to various extents. This was particularly true at 3.5% (v/v) DMSO, where k(cat) was 20-30% higher than at 1.2% DMSO, over the temperature range of 50-85 degrees C. DMSO compensated for thermal activation in some cases; for example, k(cat) at 60 degrees C in 3.5% DMSO was comparable to k(cat) at 85 degrees C in 1.2% DMSO. The relationship between DMSO activation and enzyme structural characteristics was also investigated. Nuclear magnetic resonance spectroscopy and circular dichroism showed no gross change in enzyme conformation with 3.5% DMSO between 50 and 80 degrees C. However, low levels of DMSO were shown to have a small yet significant change in enzyme conformation. This was evident through the reduction of Sso EST1's melting temperature and changes in the microenvironment of the enzyme's tyrosine and tryptophan residues at 3.5% versus 1.2% (v/v) solvent. Finally, activation parameter analysis based on kinetic data, at 1.2% and 3.5% DMSO, implied an increase in conformational flexibility with additional cosolvent. These results suggest the activating effect of DMSO was related to small changes in the enzyme's structure resulting in an increase in its conformational flexibility. Thus, in addition to their use for solubilizing hydrophobic substrates in water, cosolvents may also serve as activators in applications involving thermostable biocatalysts at sub-optimal temperatures.

The Aes protein and the monomeric alpha-galactosidase from Escherichia coli form a non-covalent complex. Implications for the regulation of carbohydrate metabolism

Aes, a 36-kDa acetylesterase from Escherichia coli, belongs to the hormone-sensitive lipase family, and it is involved in the regulation of MalT, the transcriptional activator of the maltose regulon. The activity of MalT is depressed through a direct protein-protein interaction with Aes. Although the effect is clear-cut, the meaning of this interaction and the conditions that trigger it still remain elusive. To perform a comparative thermodynamic study between the mesophilic Aes protein and two homologous thermostable enzymes, Aes was overexpressed in E. coli and purified. At the last step of the purification procedure the enzyme was eluted from a Mono Q HR 5/5 column as a major form migrating, anomalously, at 56 kDa on a calibrated Superdex 75 column. A minor peak that contains the Aes protein and a polypeptide of 50 kDa was also detected. By a combined analysis of size-exclusion chromatography and surface-enhanced laser desorption ionization-time of flight mass spectrometry, it was possible to demonstrate the presence in this peak of a stable 87-kDa complex, containing the Aes protein itself and the 50-kDa polypeptide in a 1:1 ratio. The homodimeric molecular species of Aes and of the 50-kDa polypeptide were also detected. The esterase activity associated with the 87-kDa complex, when assayed with p-nitrophenyl butanoate as substrate, proved 6-fold higher than the activity of the major Aes form of 56 kDa. Amino-terminal sequencing highlighted that the 50-kDa partner of Aes in the complex was the alpha-galactosidase from E. coli. The E. coli cells harboring plasmid pT7-SCII-aes and, therefore, expressing Aes were hampered in their growth on a minimal medium containing raffinose as a sole carbon source. Because alpha-galactosidase is involved in the metabolism of raffinose, the above findings suggest a potential role of Aes in the regulation of carbohydrate metabolism in E. coli.

Extremely stable and versatile carboxylesterase from a hyperthermophilic archaeon

We have found that the hyperthermophilic archaeon Pyrobaculum calidifontis VA1 produced a thermostable esterase. We isolated and sequenced the esterase gene (est(Pc)) from strain VA1. est(Pc) consisted of 939 bp, corresponding to 313 amino acid residues with a molecular mass of 34,354 Da. As est(Pc) showed significant identity (30%) to mammalian hormone-sensitive lipases (HSLs), esterase of P. calidifontis (Est) could be regarded as a new member of the HSL family. Activity levels of the enzyme were comparable or higher than those of previously reported enzymes not only at high temperature (6,410 U/mg at 90 degrees C), but also at ambient temperature (1,050 U/mg at 30 degrees C). The enzyme displayed extremely high thermostability and was also stable after incubation with various water-miscible organic solvents at a concentration of 80%. The enzyme also exhibited activity in the presence of organic solvents. Est of P. calidifontis showed higher hydrolytic activity towards esters with short to medium chains, with p-nitrophenyl caproate (C(6)) the best substrate among the p-nitrophenyl esters examined. As for the alcoholic moiety, the enzyme displayed esterase activity towards esters with both straight- and branched-chain alcohols. Most surprisingly, we found that this Est enzyme hydrolyzed the tertiary alcohol ester tert-butyl acetate, a feature very rare among previously reported lipolytic enzymes. The extreme stability against heat and organic solvents, along with its activity towards a tertiary alcohol ester, indicates a high potential for the Est of P. calidifontis in future applications.

The N terminus of the Escherichia coli transcription activator MalT is the domain of interaction with MalY

The maltose system of Escherichia coli consists of a number of genes encoding proteins involved in the uptake and metabolism of maltose and maltodextrins. The system is positively regulated by MalT, its transcriptional activator. MalT activity is controlled by two regulatory circuits: a positive one with maltotriose as effector and a negative one involving several proteins. MalK, the ATP-hydrolyzing subunit of the cognate ABC transporter, MalY, an enzyme with the activity of a cystathionase, and Aes, an acetyl esterase, phenotypically act as repressors of MalT activity. By in vivo titration assays, we have shown that the N-terminal 250 amino acids of MalT contain the interaction site for MalY but not for MalK. This was confirmed by gel filtration analysis, where MalY was shown to coelute with the N-terminal MalT structural domain. Mutants in MalT causing elevated mal gene expression in the absence of exogenous maltodextrins were tested in their response to the three repressors. The different MalT mutations exhibited a various degree of sensitivity towards these repressors, but none was resistant to all of them. Some of them became nearly completely resistant to Aes while still being sensitive to MalY. These mutations are located at positions 38, 220, 243, and 359, most likely defining the interaction patch with Aes on the three-dimensional structure of MalT.

Decreasing the level of ethyl acetate in ethanolic fermentation broths of Escherichia coli KO11 by expression of Pseudomonas putida estZ esterase

During the fermentation of sugars to ethanol relatively high levels of an undesirable coproduct, ethyl acetate, are also produced. With ethanologenic Escherichia coli strain KO11 as the biocatalyst, the level of ethyl acetate in beer containing 4.8% ethanol was 192 mg liter(-1). Although the E. coli genome encodes several proteins with esterase activity, neither wild-type strains nor KO11 contained significant ethyl acetate esterase activity. A simple method was developed to rapidly screen bacterial colonies for the presence of esterases which hydrolyze ethyl acetate based on pH change. This method allowed identification of Pseudomonas putida NRRL B-18435 as a source of this activity and the cloning of a new esterase gene, estZ. Recombinant EstZ esterase was purified to near homogeneity and characterized. It belongs to family IV of lipolytic enzymes and contains the conserved catalytic triad of serine, aspartic acid, and histidine. As expected, this serine esterase was inhibited by phenylmethylsulfonyl fluoride and the histidine reagent diethylpyrocarbonate. The native and subunit molecular weights of the recombinant protein were 36,000, indicating that the enzyme exists as a monomer. By using alpha-naphthyl acetate as a model substrate, optimal activity was observed at pH 7.5 and 40 degrees C. The Km and Vmax for alpha-naphthyl acetate were 18 microM and 48.1 micromol. min(-1). mg of protein(-1), respectively. Among the aliphatic esters tested, the highest activity was obtained with propyl acetate (96 micromol. min(-1). mg of protein(-1)), followed by ethyl acetate (66 micromol. min(-1). mg of protein(-1)). Expression of estZ in E. coli KO11 reduced the concentration of ethyl acetate in fermentation broth (4.8% ethanol) to less than 20 mg liter(-1).

The Aes protein directly controls the activity of MalT, the central transcriptional activator of the Escherichia coli maltose regulon

MalT, the transcriptional activator of the maltose regulon from Escherichia coli, is the prototype of a new family of transcription factors. Its activity is controlled by multiple regulatory signals. ATP and maltotriose (the inducer) are two effectors of the activator that positively control its multimerization, a critical step in promoter binding. In addition, MalK, the ABC component of the maltodextrin transport system, and the two enzymes MalY and Aes down-regulate MalT activity in vivo. By using a biochemical approach, we demonstrate here that (i) Aes controls MalT activity through direct protein-protein interaction, (ii) Aes competes with maltotriose for MalT binding, (iii) ATP and ADP differentially affect the competition between Aes and the inducer, and (iv) part, if not all, of the Aes binding site is located in DT1, the N-terminal domain of the activator, which also contains the ATP binding site. All of these characteristics point toward an identical mode of action for MalY and Aes. However, we have identified an amino acid substitution in MalT that suppresses MalT inhibition by Aes without interfering with its inhibition by MalY, suggesting that the binding sites of the two inhibitory proteins do not coincide. The differential effects of ATP and ADP on the competition between the inducer and Aes (or MalY) suggest that the ATPase activity displayed by MalT plays a role in the negative control of its activity.

Characterization of the functional interaction of adipocyte lipid-binding protein with hormone-sensitive lipase

Hormone-sensitive lipase (HSL) is an intracellular lipase that plays an important role in the hydrolysis of triacylglycerol in adipose tissue. HSL has been shown to interact with adipocyte lipid-binding protein (ALBP), a member of the family of intracellular lipid-binding proteins that bind fatty acids and other hydrophobic ligands. The current studies have addressed the functional significance of the association and mapped the site of interaction between HSL and ALBP. Incubation of homogeneous ALBP with purified, recombinant HSL in vitro resulted in a 2-fold increase in substrate hydrolysis. Moreover, the ability of oleate to inhibit HSL hydrolytic activity was attenuated by co-incubation with ALBP. Co-transfection of Chinese hamster ovary cells with HSL and ALBP resulted in greater hydrolytic activity than transfection of cells with HSL and vector alone. Deletional mutations of HSL localized the region of HSL that interacts with ALBP to amino acids 192-200, and site-directed mutagenesis of individual amino acids in this region identified His-194 and Glu-199 as critical for mediating the interaction of HSL with ALBP. Interestingly, HSL mutants H194L and E199A, each of which retained normal basal hydrolytic activity, failed to display an increase in hydrolytic activity when co-transfected with wild type ALBP. Therefore, ALBP increases the hydrolytic activity of HSL through its ability to bind and sequester fatty acids and via specific protein-protein interaction. Thus, HSL and ALBP constitute a functionally important lipolytic complex.

Stimulation of lipolysis and hormone-sensitive lipase via the extracellular signal-regulated kinase pathway

Hormonally stimulated lipolysis occurs by activation of cyclic AMP-dependent protein kinase (PKA) which phosphorylates hormone-sensitive lipase (HSL) and increases adipocyte lipolysis. Evidence suggests that catecholamines not only can activate PKA, but also the mitogen-activated protein kinase pathway and extracellular signal-regulated kinase (ERK). We now demonstrate that two different inhibitors of MEK, the upstream activator of ERK, block catecholamine- and beta(3)-stimulated lipolysis by approximately 30%. Furthermore, treatment of adipocytes with dioctanoylglycerol, which activates ERK, increases lipolysis, although MEK inhibitors decrease dioctanoylglycerol-stimulated activation of lipolysis. Using a tamoxifen regulatable Raf system expressed in 3T3-L1 preadipocytes, exposure to tamoxifen causes a 14-fold activation of ERK within 15-30 min and results in approximately 2-fold increase in HSL activity. In addition, when differentiated 3T3-L1 cells expressing the regulatable Raf were exposed to tamoxifen, a 2-fold increase in lipolysis is observed. HSL is a substrate of activated ERK and site-directed mutagenesis of putative ERK consensus phosphorylation sites in HSL identified Ser(600) as the site phosphorylated by active ERK. When S600A HSL was expressed in 3T3-L1 cells expressing the regulatable Raf, tamoxifen treatment fails to increase its activity. Thus, activation of the ERK pathway appears to be able to regulate adipocyte lipolysis by phosphorylating HSL on Ser(600) and increasing the activity of HSL.

Contribution of blotting techniques to the study of rapeseeds (Brassica napus L.) lipases

A recent advance in the study of plant lipases involving immunological techniques is presented. In an attempt to characterize lipases of cotyledons from germinating rapeseed seedlings and to investigate an eventual cross-reactivity with animal lipases, we have prepared anti-porcine pancreatic lipase antibodies raised in rabbit. It is shown by enzyme-linked immunosorbent assay and dot-blotting that these antibodies react with lipases in the rapeseed crude extract and in the different cellular fractions obtained by differential centrifugation. Preincubation of the antiserum with the rapeseed crude extract affects the amount of antibodies binding to the porcine pancreatic lipase. We demonstrate immunochemical cross-reactivity between rapeseed and porcine pancreatic lipase. Using the immunoblotting procedure, it is found that antibodies bind specifically to a single polypeptide with a molecular mass of about 55 kDa. Rapeseed lipase activity decreased after immunoprecipitation suggesting that antibodies were bound to some catalytic site residues. We conclude from the data obtained in this study that the two different lipase species present close similarities in amino acid sequence and antigen characteristics.

Hormone-sensitive lipase functions as an oligomer

Hormone-sensitive lipase (HSL) is a cytosolic neutral lipase whose activity is regulated by reversible phosphorylation and which is thought to be the rate-limiting enzyme for the mobilization of FFA from adipose tissue. In the current studies the subunit structure of HSL has been explored using sucrose gradient centrifugation and in vivo and in vitro protein-protein interactions. Evidence is provided to demonstrate that HSL exists as a functional dimer composed of homologous subunits. Dimeric HSL displayed approximately 40-fold greater activity against cholesteryl ester substrate when compared with monomeric HSL without any differences in affinity for the substrate. Truncations of HSL identified the importance of the N-terminal 300 amino acids, as well as other regions, in participating in the oligomerization of HSL. These studies support the notion that the N-terminal region of HSL represents a docking domain for protein-protein interactions and provide an additional mechanism for the posttranslational control of HSL activity in the cell via oligomerization.

Cloning, overexpression, and properties of a new thermophilic and thermostable esterase with sequence similarity to hormone-sensitive lipase subfamily from the archaeon Archaeoglobus fulgidus

A new esterase gene from the hyperthermophilic archaeon Archaeoglobus fulgidus, reported to show homology with the mammalian hormone-sensitive lipase (HSL)-like group of the esterase/lipase family, was cloned by means of the polymerase chain reaction from the A. fulgidus genome. In order to compare the biochemical properties of this putative hyperthermophilic enzyme with those of the homologous, thermophilic member of HSL group, namely Alicyclobacillus (formerly Bacillus) acidocaldarius esterase 2 (EST2), an overexpression system in Escherichia coli was established. The recombinant protein, expressed in soluble and active form at 20 mg/liter of E. coli culture, was purified to homogeneity and characterized. The enzyme, a 35.5-kDa monomeric protein, was demonstrated to be a B"-type carboxylesterase (EC 3.1.1.1) on the basis of substrate specificity and the action of inhibitors. Among the p-nitrophenyl (PNP) esters tested the best substrate was PNP-hexanoate with K(m) and k(cat) values of 11 +/- 3 microM (mean +/- SD, n = 3) and 1014 +/- 38 s(-1) (mean +/- SD, n = 3), respectively, at 70 degrees C and pH 7.1. Inactivation by diethylpyrocarbonate, phenylmethylsulfonylfluoride, diisopropylfosfofluoridate (DFP), and physostigmine, as well as labeling with [(3)H]DFP, supported our previous suggestion of a catalytic triad made up of Ser(160)-His(285)-Asp(255). The sequence identity with the thermostable A. acidocaldarius EST2 was 42.5%. The enzyme proved to be much more stable than its Alicyclobacillus counterpart. The conformational dynamics of the two proteins were investigated by frequency-domain fluorometry and anisotropy decay and the activity/stability/temperature relationship was discussed.

Homology modeling and active-site residues probing of the thermophilic Alicyclobacillus acidocaldarius esterase 2

The moderate thermophilic eubacterium Alicyclobacillus (formerly Bacillus) acidocaldarius expresses a thermostable carboxylesterase (esterase 2) belonging to the hormone-sensitive lipase (HSL)-like group of the esterase/lipase family. Based on secondary structures predictions and a secondary structure-driven multiple sequence alignment with remote homologous protein of known three-dimensional (3D) structure, we previously hypothesized for this enzyme the alpha/beta-hydrolase fold typical of several lipases and esterases and identified Ser155, Asp252, and His282 as the putative members of the catalytic triad. In this paper we report the construction of a 3D model for this enzyme based on the structure of mouse acetylcholinesterase complexed with fasciculin. The model reveals the topological organization of the fold corroborating our predictions. As regarding the active-site residues, Ser155, Asp252, and His282 are located close to each other at hydrogen bond distances. Their catalytic role was here probed by biochemical and mutagenic studies. Moreover, on the basis of the secondary structure-driven multiple sequence alignment and the 3D structural model, a residue supposed important for catalysis, Gly84, was mutated to Ser. The activity of the mutated enzyme was drastically reduced. We propose that Gly84 is part of a putative "oxyanion hole" involved in the stabilization of the transition state similar to the C group of the esterase/lipase family.

Identification of catalytically essential residues in Escherichia coli esterase by site-directed mutagenesis

Escherichia coli esterase (EcE) is a member of the hormone-sensitive lipase family. We have analyzed the roles of the conserved residues in this enzyme (His103, Glu128, Gly163, Asp164, Ser165, Gly167, Asp262, Asp266 and His292) by site-directed mutagenesis. Among them, Gly163, Asp164, Ser165, and Gly167 are the components of a G-D/E-S-A-G motif. We showed that Ser165, Asp262, and His292 are the active-site residues of the enzyme. We also showed that none of the other residues, except for Asp164, is critical for the enzymatic activity. The mutation of Asp164 to Ala dramatically reduced the catalytic efficiency of the enzyme by the factor of 10(4) without seriously affecting the substrate binding. This residue is probably structurally important to make the conformation of the active-site functional.

Interaction of rat hormone-sensitive lipase with adipocyte lipid-binding protein

Hormone-sensitive lipase (HSL) is a cytosolic neutral lipase that functions as the rate-limiting enzyme for the mobilization of free fatty acids in adipose tissue. By using the yeast two-hybrid system to examine the potential interaction of HSL with other cellular proteins, evidence is provided to demonstrate a direct interaction of HSL with adipocyte lipid-binding protein (ALBP), a member of the family of intracellular lipid-binding proteins that binds fatty acids, retinoids, and other hydrophobic ligands. The interaction was demonstrated in vitro by the binding of ALBP to HSL translated in vitro, to HSL in extracts of HSL overexpressing Chinese hamster ovary (CHO) cells, and to HSL in extracts of rat adipose tissue. Finally, the presence of ALBP was documented in immune complexes from rat adipose tissue immunoprecipitated with anti-HSL antibodies. The HSL-ALBP interaction was mapped to an N-terminal 300-aa region of HSL that is distinct from the C-terminal catalytic domain. These results suggest that HSL-derived fatty acids are bound by ALBP to facilitate intracellular trafficking of hydrophobic lipids.

Linkage map of Escherichia coli K-12, edition 10: the traditional map

This map is an update of the edition 9 map by Berlyn et al. (M. K. B. Berlyn, K. B. Low, and K. E. Rudd, p. 1715-1902, in F. C. Neidhardt et al., ed., Escherichia coli and Salmonella: cellular and molecular biology, 2nd ed., vol. 2, 1996). It uses coordinates established by the completed sequence, expressed as 100 minutes for the entire circular map, and adds new genes discovered and established since 1996 and eliminates those shown to correspond to other known genes. The latter are included as synonyms. An alphabetical list of genes showing map location, synonyms, the protein or RNA product of the gene, phenotypes of mutants, and reference citations is provided. In addition to genes known to correspond to gene sequences, other genes, often older, that are described by phenotype and older mapping techniques and that have not been correlated with sequences are included.