Structural and functional characterisation of TesA - a novel lysophospholipase A from Pseudomonas aeruginosa

Roles of Lipolytic enzymes in Mycobacterium tuberculosis pathogenesis

Mycobacterium tuberculosis (Mtb) is a bacterial pathogen that can endure for long periods in an infected patient, without causing disease. There are a number of virulence factors that increase its ability to invade the host. One of these factors is lipolytic enzymes, which play an important role in the pathogenic mechanism of Mtb. Bacterial lipolytic enzymes hydrolyze lipids in host cells, thereby releasing free fatty acids that are used as energy sources and building blocks for the synthesis of cell envelopes, in addition to regulating host immune responses. This review summarizes the relevant recent studies that used in vitro and in vivo models of infection, with particular emphasis on the virulence profile of lipolytic enzymes in Mtb. A better understanding of these enzymes will aid the development of new treatment strategies for TB. The recent work done that explored mycobacterial lipolytic enzymes and their involvement in virulence and pathogenicity was highlighted in this study. Lipolytic enzymes are expected to control Mtb and other intracellular pathogenic bacteria by targeting lipid metabolism. They are also potential candidates for the development of novel therapeutic agents.

Molecular cloning, overexpression, characterization, and In silico modelling analysis of a novel GDSL autotransporter-dependent outer membrane lipase (OML) of Pseudomonas guariconensis

The outer membrane lipase (oml) gene, encoding a novel autotransporter-dependent lipase from Pseudomonas guariconensis, was cloned and sequenced. The oml gene has an open reading frame of 1866 bp. It encodes the 621 amino acid autotransporter-dependent GDSL lipase (OML), which has the highest sequence similarity (64.08 %) with the EstA of Pseudomonas aeruginosa (PDB:3kvn.1. A). OML was expressed and purified, which showed a purified band of approximately 70 kDa. The purified enzyme showed maximum activity at pH 9 and 40 °C. Substrate specificity studies and kinetic study by Lineweaver-Burk plot of purified OML showed Km of 1.27 mM and Vmax of 333.33 U/mL with p-nitrophenyl palmitate. The purified enzyme showed good stability in the presence of hexane, methanol, and ethanol, while the presence of the metal ion Mg2+ showed maximum lipase activity. Bioinformatics analysis supported the in vitro findings by predicting enzyme substrate specificity towards long-chain fatty acids and fatty acids with shorter chain lengths. The stability of the interaction of the protein-ligand complex (OML-ricinoleic acid) was confirmed using MDS and castor oil bioconversion using purified OML was confirmed using High-Performance Liquid Chromatography (HPLC).

A strategy to enhance and modify fatty acid synthesis in Corynebacterium glutamicum and Escherichia coli: overexpression of acyl-CoA thioesterases

BACKGROUND

Fatty acid (FA) is an important platform compound for the further synthesis of high-value biofuels and oleochemicals, but chemical synthesis of FA has many limitations. One way to meet the future demand for FA could be to use microbial cell factories for FA biosynthesis.

RESULTS

Thioesterase (TE; TesA, TesB, and TE9) of Corynebacterium glutamicum (CG) can potentially improve FA biosynthesis, and tesA, tesB, and te9 were overexpressed in C. glutamicum and Escherichia coli (EC), respectively, in this study. The results showed that the total fatty acid (TFA) production of CGtesB and ECtesB significantly increased to 180.52 mg/g dry cell weight (DCW) and 123.52 mg/g DCW, respectively (P < 0.05). Overexpression strains CG and EC could increase the production of C16:0, C18:1(t), C18:2, C20:1, C16:1, C18:0, and C18:1(c) (P < 0.05), respectively, and the changes of long-chain FA resulted in the enhancement of TFA production. The enzymatic properties of TesA, TesB, and TE9 in vitro were determined: they were specific for long-, broad and short-chain substrates, respectively; the optimal temperature was 30.0 °C and the optimal acid-base (pH) were 8.0, 8.0, and 9.0, respectively; they were inhibited by Fe2+, Cu2+, Zn2+, Mg2+, and K+.

CONCLUSION

Overexpression TE enhances and modifies FA biosynthesis with multiple productive applications, and the enzyme properties provided useful clues for optimizing FA synthesis.

Marine picocyanobacterial PhnD1 shows specificity for various phosphorus sources but likely represents a constitutive inorganic phosphate transporter

Despite being fundamental to multiple biological processes, phosphorus (P) availability in marine environments is often growth-limiting, with generally low surface concentrations. Picocyanobacteria strains encode a putative ABC-type phosphite/phosphate/phosphonate transporter, phnDCE, thought to provide access to an alternative phosphorus pool. This, however, is paradoxical given most picocyanobacterial strains lack known phosphite degradation or carbon-phosphate lyase pathway to utilise alternate phosphorus pools. To understand the function of the PhnDCE transport system and its ecological consequences, we characterised the PhnD1 binding proteins from four distinct marine Synechococcus isolates (CC9311, CC9605, MITS9220, and WH8102). We show the Synechococcus PhnD1 proteins selectively bind phosphorus compounds with a stronger affinity for phosphite than for phosphate or methyl phosphonate. However, based on our comprehensive ligand screening and growth experiments showing Synechococcus strains WH8102 and MITS9220 cannot utilise phosphite or methylphosphonate as a sole phosphorus source, we hypothesise that the picocyanobacterial PhnDCE transporter is a constitutively expressed, medium-affinity phosphate transporter, and the measured affinity of PhnD1 to phosphite or methyl phosphonate is fortuitous. Our MITS9220_PhnD1 structure explains the comparatively lower affinity of picocyanobacterial PhnD1 for phosphate, resulting from a more limited H-bond network. We propose two possible physiological roles for PhnD1. First, it could function in phospholipid recycling, working together with the predicted phospholipase, TesA, and alkaline phosphatase. Second, by having multiple transporters for P (PhnDCE and Pst), picocyanobacteria could balance the need for rapid transport during transient episodes of higher P availability in the environment, with the need for efficient P utilisation in typical phosphate-deplete conditions.

Esterases as emerging biocatalysts: Mechanistic insights, genomic and metagenomic, immobilization, and biotechnological applications

Esterase enzymes are a family of hydrolases that catalyze the breakdown and formation of ester bonds. Esterases have gained a prominent position in today's world's industrial enzymes market. Due to their unique biocatalytic attributes, esterases contribute to environmentally sustainable design approaches, including biomass degradation, food and feed industry, dairy, clothing, agrochemical (herbicides, insecticides), bioremediation, biosensor development, anticancer, antitumor, gene therapy, and diagnostic purposes. Esterases can be isolated by a diverse range of mammalian tissues, animals, and microorganisms. The isolation of extremophilic esterases increases the interest of researchers in the extraction and utilization of these enzymes at the industrial level. Genomic, metagenomic, and immobilization techniques have opened innovative ways to extract esterases and utilize them for a longer time to take advantage of their beneficial activities. The current study discusses the types of esterases, metagenomic studies for exploring new esterases, and their biomedical applications in different industrial sectors.

Studies on the Selectivity Mechanism of Wild-Type E. coli Thioesterase ‘TesA and Its Mutants for Medium- and Long-Chain Acyl Substrates

E. coli thioesterase ‘TesA is an important enzyme in fatty acid production. Medium-chain fatty acids (MCFAs, C6-C10) are of great interest due to their similar physicochemical properties to petroleum-based oleo-chemicals. It has been shown that wild-type ‘TesA had better selectivity for long-chain acyl substrates (≥C16), while the two mutants ‘TesAE142D/Y145G and ‘TesAM141L/E142D/Y145G had better selectivity for medium-chain acyl substrates. However, it is difficult to obtain the selectivity mechanism of substrates for proteins by traditional experimental methods. In this study, in order to obtain more MCFAs, we analyzed the binding mode of proteins (‘TesA, ‘TesAE142D/Y145G and ‘TesAM141L/E142D/Y145G) and substrates (C16/C8-N-acetylcysteamine analogs, C16/C8-SNAC), the key residues and catalytic mechanisms through molecular docking, molecular dynamics simulations and the molecular mechanics Poisson–Boltzmann surface area (MM/PBSA). The results showed that several main residues related to catalysis, including Ser10, Asn73 and His157, had a strong hydrogen bond interaction with the substrates. The mutant region (Met141-Tyr146) and loop107–113 were mainly dominated by Van der Waals contributions to the substrates. For C16-SNAC, except for ‘TesAM141L/E142D/Y145G with large conformational changes, there were strong interactions at both head and tail ends that distorted the substrate into a more favorable high-energy conformation for the catalytic reaction. For C8-SNAC, the head and tail found it difficult to bind to the enzyme at the same time due to insufficient chain length, which made the substrate binding sites more variable, so ‘TesAM141L/E142D/Y145G with better binding sites had the strongest activity, and ‘TesA had the weakest activity, conversely. In short, the matching substrate chain and binding pocket length are the key factors affecting selectivity. This will be helpful for the further improvement of thioesterases.

Characterization of the Putative Acylated Cellulose Synthase Operon in Komagataeibacter xylinus E25

Bacterial cellulose is a natural polymer with an expanding array of applications. Because of this, the main cellulose producers of the Komagataeibacter genus have been extensively studied with the aim to increase its synthesis or to customize its physicochemical features. Up to now, the genetic studies in Komagataeibacter have focused on the first cellulose synthase operon (bcsI) encoding the main enzyme complex. However, the role of other accessory cellulose operons has been understudied. Here we aimed to fill this gap by performing a detailed analysis of the second cellulose synthase operon (bcsII), which is putatively linked with cellulose acylation. In this study we harnessed the genome sequence, gene expression and protein structure information of K. xylinus E25 and other Komagataeibacter species to discuss the probable features of bcsII and the biochemical function of its main protein products. The results of our study support the previous hypothesis that bcsII is involved in the synthesis of the acylated polymer and expand it by presenting the evidence that it may also function in the regulation of its attachment to the cell surface and to the crystalline cellulose fibers.

Structural, mechanistic, and physiological insights into phospholipase A-mediated membrane phospholipid degradation in Pseudomonas aeruginosa

Cells steadily adapt their membrane glycerophospholipid (GPL) composition to changing environmental and developmental conditions. While the regulation of membrane homeostasis via GPL synthesis in bacteria has been studied in detail, the mechanisms underlying the controlled degradation of endogenous GPLs remain unknown. Thus far, the function of intracellular phospholipases A (PLAs) in GPL remodeling (Lands cycle) in bacteria is not clearly established. Here, we identified the first cytoplasmic membrane-bound phospholipase A1 (PlaF) from Pseudomonas aeruginosa, which might be involved in the Lands cycle. PlaF is an important virulence factor, as the P. aeruginosa ΔplaF mutant showed strongly attenuated virulence in Galleria mellonella and macrophages. We present a 2.0-Å-resolution crystal structure of PlaF, the first structure that reveals homodimerization of a single-pass transmembrane (TM) full-length protein. PlaF dimerization, mediated solely through the intermolecular interactions of TM and juxtamembrane regions, inhibits its activity. The dimerization site and the catalytic sites are linked by an intricate ligand-mediated interaction network, which might explain the product (fatty acid) feedback inhibition observed with the purified PlaF protein. We used molecular dynamics simulations and configurational free energy computations to suggest a model of PlaF activation through a coupled monomerization and tilting of the monomer in the membrane, which constrains the active site cavity into contact with the GPL substrates. Thus, these data show the importance of the PlaF-mediated GPL remodeling pathway for virulence and could pave the way for the development of novel therapeutics targeting PlaF.

Elucidating Sequence and Structural Determinants of Carbohydrate Esterases for Complete Deacetylation of Substituted Xylans

Acetylated glucuronoxylan is one of the most common types of hemicellulose in nature. The structure is formed by a β-(1→4)-linked D-xylopyranosyl (Xylp) backbone that can be substituted with an acetyl group at O-2 and O-3 positions, and α-(1→2)-linked 4-O-methylglucopyranosyluronic acid (MeGlcpA). Acetyl xylan esterases (AcXE) that target mono- or doubly acetylated Xylp are well characterized; however, the previously studied AcXE from Flavobacterium johnsoniae (FjoAcXE) was the first to remove the acetyl group from 2-O-MeGlcpA-3-O-acetyl-substituted Xylp units, yet structural characteristics of these enzymes remain unspecified. Here, six homologs of FjoAcXE were produced and three crystal structures of the enzymes were solved. Two of them are complex structures, one with bound MeGlcpA and another with acetate. All homologs were confirmed to release acetate from 2-O-MeGlcpA-3-O-acetyl-substituted xylan, and the crystal structures point to key structural elements that might serve as defining features of this unclassified carbohydrate esterase family. Enzymes comprised two domains: N-terminal CBM domain and a C-terminal SGNH domain. In FjoAcXE and all studied homologs, the sequence motif around the catalytic serine is Gly-Asn-Ser-Ile (GNSI), which differs from other SGNH hydrolases. Binding by the MeGlcpA-Xylp ligand is directed by positively charged and highly conserved residues at the interface of the CBM and SGNH domains of the enzyme.

Thioesterase enzyme families: Functions, structures, and mechanisms

Thioesterases are enzymes that hydrolyze thioester bonds in numerous biochemical pathways, for example in fatty acid synthesis. This work reports known functions, structures, and mechanisms of updated thioesterase enzyme families, which are classified into 35 families based on sequence similarity. Each thioesterase family is based on at least one experimentally characterized enzyme, and most families have enzymes that have been crystallized and their tertiary structure resolved. Classifying thioesterases into families allows to predict tertiary structures and infer catalytic residues and mechanisms of all sequences in a family, which is particularly useful because the majority of known protein sequence have no experimental characterization. Phylogenetic analysis of experimentally characterized thioesterases that have structures with the two main structural folds reveal convergent and divergent evolution. Based on tertiary structure superimposition, catalytic residues are predicted.

Extracellular degradation of a polyurethane oligomer involving outer membrane vesicles and further insights on the degradation of 2,4-diaminotoluene in Pseudomonas capeferrum TDA1

The continuing reports of plastic pollution in various ecosystems highlight the threat posed by the ever-increasing consumption of synthetic polymers. Therefore, Pseudomonas capeferrum TDA1, a strain recently isolated from a plastic dump site, was examined further regarding its ability to degrade polyurethane (PU) compounds. The previously reported degradation pathway for 2,4-toluene diamine, a precursor and degradation intermediate of PU, could be confirmed by RNA-seq in this organism. In addition, different cell fractions of cells grown on a PU oligomer were tested for extracellular hydrolytic activity using a standard assay. Strikingly, purified outer membrane vesicles (OMV) of P. capeferrum TDA1 grown on a PU oligomer showed higher esterase activity than cell pellets. Hydrolases in the OMV fraction possibly involved in extracellular PU degradation were identified by mass spectrometry. On this basis, we propose a model for extracellular degradation of polyester-based PUs by P. capeferrum TDA1 involving the role of OMVs in synthetic polymer degradation.

Substrate Access Mechanism in a Novel Membrane-Bound Phospholipase A of Pseudomonas aeruginosa Concordant with Specificity and Regioselectivity

PlaF is a cytoplasmic membrane-bound phospholipase A₁ from Pseudomonas aeruginosa that alters the membrane glycerophospholipid (GPL) composition and fosters the virulence of this human pathogen. PlaF activity is regulated by a dimer-to-monomer transition followed by tilting of the monomer in the membrane. However, how substrates reach the active site and how the characteristics of the active site tunnels determine the activity, specificity, and regioselectivity of PlaF for natural GPL substrates have remained elusive. Here, we combined unbiased and biased all-atom molecular dynamics (MD) simulations and configurational free-energy computations to identify access pathways of GPL substrates to the catalytic center of PlaF. Our results map out a distinct tunnel through which substrates access the catalytic center. PlaF variants with bulky tryptophan residues in this tunnel revealed decreased catalysis rates due to tunnel blockage. The MD simulations suggest that GPLs preferably enter the active site with the sn-1 acyl chain first, which agrees with the experimentally demonstrated PLA₁ activity of PlaF. We propose that the acyl chain-length specificity of PlaF is determined by the structural features of the access tunnel, which results in favorable free energy of binding of medium-chain GPLs. The suggested egress route conveys fatty acid (FA) products to the dimerization interface and, thus, contributes to understanding the product feedback regulation of PlaF by FA-triggered dimerization. These findings open up opportunities for developing potential PlaF inhibitors, which may act as antibiotics against P. aeruginosa.

Identification and Characterization of a Novel Thermostable GDSL-Type Lipase from Geobacillus thermocatenulatus

Two putative genes, lip29 and est29, encoding lipolytic enzymes from the thermophilic bacterium Geobacillus thermocatenulatus KCTC 3921 were cloned and overexpressed in Escherichia coli. The recombinant Lip29 and Est29 were purified 67.3-fold to homogeneity with specific activity of 2.27 U/mg and recovery of 5.8% and 14.4-fold with specific activity of 0.92 U/mg and recovery of 1.3%, respectively. The molecular mass of each purified enzyme was estimated to be 29 kDa by SDSPAGE. The alignment analysis of amino acid sequences revealed that both enzymes belonged to GDSL lipase/esterase family including conserved blocks with SGNH catalytic residues which was mainly identified in plants before. While Est29 showed high specificity toward short-chain fatty acids (C4-C8), Lip29 showed strong lipolytic activity to long-chain fatty acids (C12-C16). The optimal activity of Lip29 toward p-nitrophenyl palmitate as a substrate was observed at 50°C and pH 9.5, respectively, and its activity was maintained more than 24 h at optimal temperatures, indicating that Lip29 was thermostable. Lip29 exhibited high tolerance against detergents and metal ions. The homology modeling and substrate docking revealed that the long-chain substrates showed the greatest binding affinity toward enzyme. Based on the biochemical and in silico analyses, we present for the first time a GDSL-type lipase in the thermophilic bacteria group.

Rv3091, An Extracellular Patatin-Like Phospholipase in Mycobacterium tuberculosis, Prolongs Intracellular Survival of Recombinant Mycolicibacterium smegmatis by Mediating Phagosomal Escape

Patatin-like phospholipases (PLPs) are important virulence factors of many pathogens. However, there are no prevailing studies regarding PLPs as a virulence factor of Mycobacterium tuberculosis (Mtb). Analysis of Rv3091, a putative protein of Mtb, shows that it belongs to the PLPs family. Here, we cloned and expressed the rv3091 gene in Mycobacterium smegmatis and, subsequently, conducted protein purification and characterization. We show that it possesses phospholipase A₁, phospholipase A₂, and lipase activity. We confirm the putative active site residues, namely, Ser214 and Asp407, using site directed mutagenesis. The Rv3091 is an extracellular protein that alters the colony morphology of M. smegmatis. The presence of Rv3091 enhances the intracellular survival capability of M. smegmatis in murine peritoneal macrophages. Additionally, it promotes M. smegmatis phagosomal escape from macrophages. Moreover, Rv3091 significantly increased the survival of M. smegmatis and aggravated lesions in C57BL/6 J murine lungs in vivo. Taken together, our results indicate that Rv3091 as an extracellular PLP that is critical to the pathogenicity of mycobacterium as it allows mycobacterium to utilize phospholipids for its growth and provides resistance to phagosome killing, resulting in its enhanced intracellular survival.

Characterisation of a lysophospholipase from Lactobacillus mucosae

OBJECTIVE

In this study, we characterised a novel lysophospholipase (LysoPL) from the L. mucosae LM1 strain. The gene, LM-lysoPL, encoding LysoPL from L. mucosae LM1 was cloned, analyzed, and expressed.

RESULTS

LM-lysoPL contained a conserved region and catalytic triad motif responsible for lysophospholipase activity. After purification, UHPLC-MS analysis showed that recombinant LM-LysoPL hydrolyzed phosphatidic acid, generating lysophosphatidic acid. The enzyme had greater hydrolytic activity against C16 and C18 fatty acids, indicating a preference for long-chain fatty acids. Enzymatic assays showed that the optimal pH and temperature of recombinant LM-LysoPL were 7 and 30 °C, respectively, and it was enzymatically active within a narrow pH range.

CONCLUSIONS

To the best of our knowledge, this is the first study to identify and characterize a lysophospholipase from lactic acid bacteria. Our findings provide a basis for understanding the probiotic role of L. mucosae LM1 in the gut.

Structure, function, and regulation of thioesterases

Thioesterases are present in all living cells and perform a wide range of important biological functions by catalysing the cleavage of thioester bonds present in a diverse array of cellular substrates. Thioesterases are organised into 25 families based on their sequence conservation, tertiary and quaternary structure, active site configuration, and substrate specificity. Recent structural and functional characterisation of thioesterases has led to significant changes in our understanding of the regulatory mechanisms that govern enzyme activity and their respective cellular roles. The resulting dogma changes in thioesterase regulation include mechanistic insights into ATP and GDP-mediated regulation by oligomerisation, the role of new key regulatory regions, and new insights into a conserved quaternary structure within TE4 family members. Here we provide a current and comparative snapshot of our understanding of thioesterase structure, function, and regulation across the different thioesterase families.

The substrate selectivity of the two homologous SGNH hydrolases from Streptomyces bacteria: Molecular dynamics and experimental study

Two extracellular enzymes of the SGNH hydrolase superfamily reveal highly homologous 3D structures, but act on different substrates; one is a true phospholipase A1 from Streptomyces albidoflavus (SaPLA1, EC: 3.1.1.32, PDB code: 4HYQ), whereas the promiscuous enzyme from Streptomyces rimosus (SrLip, EC: 3.1.1.3, PDB code: 5MAL) exhibits lipase, phospholipase, esterase, thioesterase, and Tweenase activities. To get insight into binding modes of phospholipid and triglyceride substrates in both enzymes and understand their chain-length preferences, we opted for computational approach based on in silico prepared enzyme-substrate complexes. Docking procedure and molecular dynamics simulations at microsecond time scale were applied. The modelled complexes of SaPLA1 and SrLip enzymes revealed substrate accommodation: a) the acyl-chain attached to sn-1 position fits into the hydrophobic pocket, b) the acyl-chain attached to sn-2 position fits in the hydrophobic cleft, whereas c) the sn-3 bound acyl chain of the triglyceride or polar head of the glycerophospholipid fits into the binding groove. Moreover, our results pinpointed subtle amino acid differences in the hydrophobic pockets of these two enzymes which accommodate the acyl chain attached to sn-1 position of glycerol to be responsible for the chain length preference. Slight differences in the binding grooves of SaPLA1 and SrLip, which accommodate the acyl chain attached to sn-3 position are responsible for exclusive phospholipase and both phospholipase/lipase activities of these two enzymes, respectively. The results of modelling correlate with the experimentally obtained kinetic parameters given in the literature and are important for protein engineering that aims to obtain a variant of enzyme, which would preferably act on the substrate of interest.

Biodiesel and flavor compound production using a novel promiscuous cold-adapted SGNH-type lipase (HaSGNH1) from the psychrophilic bacterium Halocynthiibacter arcticus

BACKGROUND

Biodiesel and flavor compound production using enzymatic transesterification by microbial lipases provides mild reaction conditions and low energy cost compared to the chemical process. SGNH-type lipases are very effective catalysts for enzymatic transesterification due to their high reaction rate, great stability, relatively small size for convenient genetic manipulations, and ease of immobilization. Hence, it is highly important to identify novel SGNH-type lipases with high catalytic efficiencies and good stabilities.

RESULTS

A promiscuous cold-adapted SGNH-type lipase (HaSGNH1) from Halocynthiibacter arcticus was catalytically characterized and functionally explored. HaSGNH1 displayed broad substrate specificity that included tert-butyl acetate, glucose pentaacetate, and p-nitrophenyl esters with excellent stability and high efficiency. Important amino acids (N83, M86, R87, F131, and I173F) around the substrate-binding pocket were shown to be responsible for catalytic activity, substrate specificity, and reaction kinetics. Moreover, immobilized HaSGNH1 was used to produce high yields of butyl and oleic esters.

CONCLUSIONS

This work provides a molecular understanding of substrate specificities, catalytic regulation, immobilization, and industrial applications of a promiscuous cold-adapted SGNH-type lipase (HaSGNH1) from H. arcticus. This is the first analysis on biodiesel and flavor synthesis using a cold-adapted halophilic SGNH-type lipase from a Halocynthiibacter species.

Study on a Novel Cold-Active and Halotolerant Monoacylglycerol Lipase Widespread in Marine Bacteria Reveals a New Group of Bacterial Monoacylglycerol Lipases Containing Unusual C(A/S)HSMG Catalytic Motifs

Monoacylglycerol lipases (MGLs) are present in all domains of life. However, reports on bacterial MGLs are still limited. Until now, reported bacterial MGLs are all thermophilic/mesophilic enzymes from warm terrestrial environments or deep-sea hydrothermal vent, and none of them originates from marine environments vastly subject to low temperature, high salts, and oligotrophy. Here, we characterized a novel MGL, GnMgl, from the marine cold-adapted and halophilic bacterium Glaciecola nitratireducens FR1064^T. GnMgl shares quite low sequence similarities with characterized MGLs (lower than 31%). GnMgl and most of its bacterial homologs harbor a catalytic Ser residue located in the conserved C(A/S)HSMG motif rather than in the typical GxSxG motif reported on other MGLs, suggesting that GnMgl-like enzymes might be different from reported MGLs in catalysis. Phylogenetic analysis suggested that GnMgl and its bacterial homologs are clustered as a separate group in the monoglyceridelipase_lysophospholipase family of the Hydrolase_4 superfamily. Recombinant GnMgl has no lysophospholipase activity but could hydrolyze saturated (C12:0-C16:0) and unsaturated (C18:1 and C18:2) MGs and short-chain triacylglycerols, displaying distinct substrate selectivity from those of reported bacterial MGLs. The substrate preference of GnMgl, predicted to be a membrane protein, correlates to the most abundant fatty acids within the strain FR1064^T, suggesting the role of GnMgl in the lipid catabolism in this marine bacterium. In addition, different from known bacterial MGLs that are all thermostable enzymes, GnMgl is a cold-adapted enzyme, with the maximum activity at 30°C and retaining 30% activity at 0°C. GnMgl is also a halotolerant enzyme with full activity in 3.5M NaCl. The cold-adapted and salt-tolerant characteristics of GnMgl may help its source strain FR1064^T adapt to the cold and saline marine environment. Moreover, homologs to GnMgl are found to be abundant in various marine bacteria, implying their important physiological role in these marine bacteria. Our results on GnMgl shed light on marine MGLs.

Structure-guided protein engineering increases enzymatic activities of the SGNH family esterases

BACKGROUND

Esterases and lipases hydrolyze short-chain esters and long-chain triglycerides, respectively, and therefore play essential roles in the synthesis and decomposition of ester bonds in the pharmaceutical and food industries. Many SGNH family esterases share high similarity in sequences. However, they have distinct enzymatic activities toward the same substrates. Due to a lack of structural information, the detailed catalytic mechanisms of these esterases remain barely investigated.

RESULTS

In this study, we identified two SGNH family esterases, CrmE10 and AlinE4, from marine bacteria with significantly different preferences for pH, temperature, metal ion, and organic solvent tolerance despite high sequence similarity. The crystal structures of these two esterases, including wild type and mutants, were determined to high resolutions ranging from 1.18 Å to 2.24 Å. Both CrmE10 and AlinE4 were composed of five β-strands and nine α-helices, which formed one compact N-terminal α/β globular domain and one extended C-terminal domain. The aspartic residues (D178 in CrmE10/D162 in AlinE4) destabilized the conformations of the catalytic triad (Ser-Asp-His) in both esterases, and the metal ion Cd²⁺ might reduce enzymatic activity by blocking proton transfer or substrate binding. CrmE10 and AlinE4 showed distinctly different electrostatic surface potentials, despite the similar atomic architectures and a similar swap catalytic mechanism. When five negatively charged residues (Asp or Glu) were mutated to residue Lys, CrmE10 obtained elevated alkaline adaptability and significantly increased the enzymatic activity from 0 to 20% at pH 10.5. Also, CrmE10 mutants exhibited dramatic change for enzymatic properties when compared with the wide-type enzyme.

CONCLUSIONS

These findings offer a perspective for understanding the catalytic mechanism of different esterases and might facilitate the industrial biocatalytic applications.

Carboxylic Ester Hydrolases in Bacteria: Active Site, Structure, Function and Application

Carboxylic ester hydrolases (CEHs), which catalyze the hydrolysis of carboxylic esters to produce alcohol and acid, are identified in three domains of life. In the Protein Data Bank (PDB), 136 crystal structures of bacterial CEHs (424 PDB codes) from 52 genera and metagenome have been reported. In this review, we categorize these structures based on catalytic machinery, structure and substrate specificity to provide a comprehensive understanding of the bacterial CEHs. CEHs use Ser, Asp or water as a nucleophile to drive diverse catalytic machinery. The α/β/α sandwich architecture is most frequently found in CEHs, but 3-solenoid, β-barrel, up-down bundle, α/β/β/α 4-layer sandwich, 6 or 7 propeller and α/β barrel architectures are also found in these CEHs. Most are substrate-specific to various esters with types of head group and lengths of the acyl chain, but some CEHs exhibit peptidase or lactamase activities. CEHs are widely used in industrial applications, and are the objects of research in structure- or mutation-based protein engineering. Structural studies of CEHs are still necessary for understanding their biological roles, identifying their structure-based functions and structure-based engineering and their potential industrial applications.

Insights into the Periplasmic Proteins of Acinetobacter baumannii AB5075 and the Impact of Imipenem Exposure: A Proteomic Approach

Carbapenem-resistant Acinetobacter baumannii strains cause life-threatening infections due to the lack of therapeutic options. Although the main mechanisms underlying antibiotic-resistance have been extensively studied, the general response to maintain bacterial viability under antibiotic exposure deserves to be fully investigated. Since the periplasmic space contains several proteins with crucial cellular functions, besides carbapenemases, we decided to study the periplasmic proteome of the multidrug-resistant (MDR) A. baumannii AB5075 strain, grown in the absence and presence of imipenem (IMP). Through the proteomic approach, 65 unique periplasmic proteins common in both growth conditions were identified: eight proteins involved in protein fate, response to oxidative stress, energy metabolism, antibiotic-resistance, were differentially expressed. Among them, ABUW_1746 and ABUW_2363 gene products presented the tetratricopeptide repeat motif, mediating protein-protein interactions. The expression switch of these proteins might determine specific protein interactions to better adapt to changing environmental conditions. ABUW_2868, encoding a heat shock protein likely involved in protection against oxidative stress, was upregulated in IMP-exposed bacteria. Accordingly, the addition of periplasmic proteins from A. baumannii cultured with IMP increased bacterial viability in an antioxidant activity assay. Overall, this study provides the first insights about the composition of the periplasmic proteins of a MDR A. baumannii strain, its biological response to IMP and suggests possible new targets to develop alternative antibiotic drugs.

Rv1075c of Mycobacterium tuberculosis is a GDSL-Like Esterase and Is Important for Intracellular Survival

Mycobacterium tuberculosis lipid metabolism pathways facilitate access to carbon and energy sources during infection. M. tuberculosis gene Rv1075c was annotated as a conserved hypothetical protein. We identified that Rv1075c amino acid sequence shares similarities with other bacterial lipase/esterases and we demonstrated that it has esterase activity, with preference for short-chain fatty acids, particularly acetate, with highest activity at 45°C, pH 9. Site-direct mutagenesis revealed its activity triad as Ser80, Asp244, and His247. We further determined that rRv1075c hydrolyzed triacetin and tributyrin, and it was mainly distributed in cell wall and membrane. Its expression was induced at pH 4.5, mimicking the acidic phagosome of macrophages. Mutation of Rv1075c led to reduced bacterial growth in THP-1 cells and human peripheral blood mononuclear cell-derived macrophages, and attenuated M. tuberculosis infection in mice. Our data suggest that Rv1075c is involved in ester and fatty acid metabolism inside host cells.

Microbial esterases and ester prodrugs: An unlikely marriage for combating antibiotic resistance

The rise of antibiotic resistance necessitates the search for new platforms for drug development. Prodrugs are common tools for overcoming drawbacks typically associated with drug formulation and delivery, with ester prodrugs providing a classic strategy for masking polar alcohol and carboxylic acid functionalities and improving cell permeability. Ester prodrugs are normally designed to have simple ester groups, as they are expected to be cleaved and reactivated by a wide spectrum of cellular esterases. However, a number of pathogenic and commensal microbial esterases have been found to possess significant substrate specificity and can play an unexpected role in drug metabolism. Ester protection can also introduce antimicrobial properties into previously nontoxic drugs through alterations in cell permeability or solubility. Finally, mutation to microbial esterases is a novel mechanism for the development of antibiotic resistance. In this review, we highlight the important pathogenic and xenobiotic functions of microbial esterases and discuss the development and application of ester prodrugs for targeting microbial infections and combating antibiotic resistance. Esterases are often overlooked as therapeutic targets. Yet, with the growing need to develop new antibiotics, a thorough understanding of the specificity and function of microbial esterases and their combined action with ester prodrug antibiotics will support the design of future therapeutics.

Matching Protein Interfaces for Improved Medium-Chain Fatty Acid Production

Medium-chain fatty acids (MCFAs) are key intermediates in the synthesis of medium-chain chemicals including α-olefins and dicarboxylic acids. In bacteria, microbial production of MCFAs is limited by the activity and product profile of fatty acyl-ACP thioesterases. Here, we engineer a heterologous bacterial medium-chain fatty acyl-ACP thioesterase for improved MCFA production in Escherichia coli. Electrostatically matching the interface between the heterologous medium-chain Acinetobacter baylyi fatty acyl-ACP thioesterase (AbTE) and the endogenous E. coli fatty acid ACP ( E. coli AcpP) by replacing small nonpolar amino acids on the AbTE surface for positively charged ones increased secreted MCFA titers more than 3-fold. Nuclear magnetic resonance titration of E. coli ¹⁵N-octanoyl-AcpP with a single AbTE point mutant and the best double mutant showed a progressive and significant increase in the number of interactions when compared to AbTE wildtype. The best AbTE mutant produced 131 mg/L of MCFAs, with MCFAs being 80% of all secreted fatty acid chain lengths after 72 h. To enable the future screening of larger numbers of AbTE variants to further improve MCFA titers, we show that a previously developed G-protein coupled receptor (GPCR)-based MCFA sensor differentially detects MCFAs secreted by E. coli expressing different AbTE variants. This work demonstrates that engineering the interface of heterologous enzymes to better couple with endogenous host proteins is a useful strategy to increase the titers of microbially produced chemicals. Further, this work shows that GPCR-based sensors are producer microbe agnostic and can detect chemicals directly in the producer microbe supernatant, setting the stage for the sensor-guided engineering of MCFA producing microbes.

Identification and characterization of a novel esterase from Thauera sp

A novel esterase gene TLip was identified from the strain Thauera sp. and expressed at high levels in Escherichia coli. The TLip protein shared the highest identity (48%) to esterase TesA from Pseudomonas aeruginosa when compared to enzymes with reported properties. Phylogenetic analysis showed that TLip belongs to the GDSL family of bacterial lipolytic enzymes. TLip was an alkaline esterase with a broad optimal temperature range 37-50 °C and an optimal pH of 8.0. Substrate specificity assays showed that TLip preferred medium chain p-nitrophenyl esters (C₆ -C₁₂ ). Besides, the activity of TLip was strongly inhibited by Cu²⁺ but greatly enhanced by Triton X-100 and Tween 80. Thermostability assay revealed that TLip was stable without loss of activity at 37 °C and still retained 69% activity at 50 °C after 2 H of incubation. Together, these provided a good candidate for further exploration of TLip as a promising biocatalyst in industry.

Microbial synthesis of medium-chain chemicals from renewables

Linear, medium-chain (C8-C12) hydrocarbons are important components of fuels as well as commodity and specialty chemicals. As industrial microbes do not contain pathways to produce medium-chain chemicals, approaches such as overexpression of endogenous enzymes or deletion of competing pathways are not available to the metabolic engineer; instead, fatty acid synthesis and reversed β-oxidation are manipulated to synthesize medium-chain chemical precursors. Even so, chain lengths remain difficult to control, which means that purification must be used to obtain the desired products, titers of which are typically low and rarely exceed milligrams per liter. By engineering the substrate specificity and activity of the pathway enzymes that generate the fatty acyl intermediates and chain-tailoring enzymes, researchers can boost the type and yield of medium-chain chemicals. Development of technologies to both manipulate chain-tailoring enzymes and to assay for products promises to enable the generation of g/L yields of medium-chain chemicals.

Catalytic Dyad in the SGNH Hydrolase Superfamily: In-depth Insight into Structural Parameters Tuning the Catalytic Process of Extracellular Lipase from Streptomyces rimosus

SrLip is an extracellular enzyme from Streptomyces rimosus (Q93MW7) exhibiting lipase, phospholipase, esterase, thioesterase, and tweenase activities. The structure of SrLip is one of a very few lipases, among the 3D-structures of the SGNH superfamily of hydrolases, structurally characterized by synchrotron diffraction data at 1.75 Å resolution (PDB: 5MAL ). Its crystal structure was determined by molecular replacement using a homology model based on the crystal structure of phospholipase A₁ from Streptomyces albidoflavus (PDB: 4HYQ ). The structure reveals the Rossmann-like 3-layer αβα sandwich fold typical of the SGNH superfamily stabilized by three disulfide bonds. The active site shows a catalytic dyad involving Ser10 and His216 with Ser10-OγH···NεHis216, His216-NδH···O═C-Ser214, and Gly54-NH···Oγ-Ser10 hydrogen bonds essential for the catalysis; the carbonyl oxygen of the Ser214 main chain acts as a hydrogen bond acceptor ensuring the orientation of the His216 imidazole ring suitable for a proton transfer. Molecular dynamics simulations of the apoenzyme and its complex with p-nitrophenyl caprylate were used to probe the positioning of the substrate ester group within the active site and its aliphatic chain within the binding site. Quantum-mechanical calculations at the DFT level revealed the precise molecular mechanism of the SrLip catalytic activity, demonstrating that the overall hydrolysis is a two-step process with acylation as the rate-limiting step associated with the activation free energy of ΔG^⧧_ENZ = 17.9 kcal mol^-1, being in reasonable agreement with the experimental value of 14.5 kcal mol^-1, thus providing strong support in favor of the proposed catalytic mechanism based on a dyad.

Evaluation of thioesterases from Acinetobacter baylyi for production of free fatty acids

Acinetobacter baylyi is one of few Gram-negative bacteria capable of accumulating storage lipids in the form of triacylglycerides and wax esters, which makes it an attractive candidate for production of lipophilic products, including biofuel precursors. Thioesterases play a significant dual role in the triacylglyceride and wax ester biosynthesis by either providing or removing acyl-CoA from this pathway. Therefore, 4 different thioesterase genes were cloned from Acinetobacter baylyi ADP1 and expressed in Escherichia coli to investigate their contribution to free fatty acids (FFAs) accumulation. Overexpression of the genes tesA' (a leaderless form of the gene tesA) and tesC resulted in increased accumulation of FFAs when compared with the host E. coli strain. Overexpression of tesA' showed a 1.87-fold increase in production of long-chain fatty acids (C16 to C18) over the host strain. Unlike TesC and the other investigated thioesterases, the TesA' thioesterase also produced shorter chain FFAs (e.g., myristic acid) and unsaturated FFAs (e.g., cis-vaccenic acid (18:1Δ11)). A comparison of the remaining 3 A. baylyi ADP1 thioesterases (encoded by the tesB, tesC, and tesD genes) revealed that only the strain containing the tesC gene produced statistically higher levels of FFAs over the control, suggesting that it possesses the acyl-ACP thioesterase activity. Both E. coli strains containing the tesB and tesD genes produced levels of FFAs similar to those of the plasmid-free control E. coli strain, which indicates that TesB and TesD lack the acyl-ACP thioesterase activity.

Simple discovery of bacterial biocatalysts from environmental samples through functional metaproteomics

Bacterial biocatalysts play a key role in our transition to a bio-based, post-petroleum economy. However, the discovery of new biocatalysts is currently limited by our ability to analyze genomic information and our capacity of functionally screening for desired activities. Here, we present a simple workflow that combines functional metaproteomics and metagenomics, which facilitates the unmediated and direct discovery of biocatalysts in environmental samples. To identify the entirety of lipolytic biocatalysts in a soil sample contaminated with used cooking oil, we detected all proteins active against a fluorogenic substrate in sample's metaproteome using a 2D-gel zymogram. Enzymes' primary structures were then deduced by tryptic in-gel digest and mass spectrometry of the active protein spots, searching against a metagenome database created from the same contaminated soil sample. We then expressed one of the novel biocatalysts heterologously in Escherichia coli and obtained proof of lipolytic activity.

Novel insights into biosynthesis and uptake of rhamnolipids and their precursors

The human pathogenic bacterium Pseudomonas aeruginosa produces rhamnolipids, glycolipids with functions for bacterial motility, biofilm formation, and uptake of hydrophobic substrates. Rhamnolipids represent a chemically heterogeneous group of secondary metabolites composed of one or two rhamnose molecules linked to one or mostly two 3-hydroxyfatty acids of various chain lengths. The biosynthetic pathway involves rhamnosyltransferase I encoded by the rhlAB operon, which synthesizes 3-(3-hydroxyalkanoyloxy)alkanoic acids (HAAs) followed by their coupling to one rhamnose moiety. The resulting mono-rhamnolipids are converted to di-rhamnolipids in a third reaction catalyzed by the rhamnosyltransferase II RhlC. However, the mechanism behind the biosynthesis of rhamnolipids containing only a single fatty acid is still unknown. To understand the role of proteins involved in rhamnolipid biosynthesis the heterologous expression of rhl-genes in non-pathogenic Pseudomonas putida KT2440 strains was used in this study to circumvent the complex quorum sensing regulation in P. aeruginosa. Our results reveal that RhlA and RhlB are independently involved in rhamnolipid biosynthesis and not in the form of a RhlAB heterodimer complex as it has been previously postulated. Furthermore, we demonstrate that mono-rhamnolipids provided extracellularly as well as HAAs as their precursors are generally taken up into the cell and are subsequently converted to di-rhamnolipids by P. putida and the native host P. aeruginosa. Finally, our results throw light on the biosynthesis of rhamnolipids containing one fatty acid, which occurs by hydrolyzation of typical rhamnolipids containing two fatty acids, valuable for the production of designer rhamnolipids with desired physicochemical properties.

PpEst is a novel PBAT degrading polyesterase identified by proteomic screening of Pseudomonas pseudoalcaligenes

A novel esterase, PpEst, that hydrolyses the co-aromatic-aliphatic polyester poly(1,4-butylene adipate-co-terephthalate) (PBAT) was identified by proteomic screening of the Pseudomonas pseudoalcaligenes secretome. PpEst was induced by the presence of PBAT in the growth media and had predicted arylesterase (EC 3.1.1.2) activity. PpEst showed polyesterase activity on both whole and milled PBAT film releasing terephthalic acid and 4-(4-hydroxybutoxycarbonyl)benzoic acid while end product inhibition by 4-(4-hydroxybutoxycarbonyl)benzoic acid was observed. Modelling of an aromatic polyester mimicking oligomer into the PpEst active site indicated that the binding pocket could be big enough to accommodate large polymers. This is the first report of a PBAT degrading enzyme being identified by proteomic screening and shows that this approach can contribute to the discovery of new polymer hydrolysing enzymes. Moreover, these results indicate that arylesterases could be an interesting enzyme class for identifications of polyesterases.

(Meta)genomic insights into the pathogenome of Cellulosimicrobium cellulans

Despite having serious clinical manifestations, Cellulosimicrobium cellulans remain under-reported with only three genome sequences available at the time of writing. Genome sequences of C. cellulans LMG16121, C. cellulans J36 and Cellulosimicrobium sp. strain MM were used to determine distribution of pathogenicity islands (PAIs) across C. cellulans, which revealed 49 potential marker genes with known association to human infections, e.g. Fic and VbhA toxin-antitoxin system. Oligonucleotide composition-based analysis of orthologous proteins (n = 791) across three genomes revealed significant negative correlation (P < 0.05) between frequency of optimal codons (F_opt) and gene G+C content, highlighting the G+C-biased gene conversion (gBGC) effect across Cellulosimicrobium strains. Bayesian molecular-clock analysis performed on three virulent PAI proteins (Fic; D-alanyl-D-alanine-carboxypeptidase; transposase) dated the divergence event at 300 million years ago from the most common recent ancestor. Synteny-based annotation of hypothetical proteins highlighted gene transfers from non-pathogenic bacteria as a key factor in the evolution of PAIs. Additonally, deciphering the metagenomic islands using strain MM’s genome with environmental data from the site of isolation (hot-spring biofilm) revealed (an)aerobic respiration as population segregation factor across the in situ cohorts. Using reference genomes and metagenomic data, our results highlight the emergence and evolution of PAIs in the genus Cellulosimicrobium.

A membrane-bound esterase PA2949 from Pseudomonas aeruginosa is expressed and purified from Escherichia coli

Pseudomonas aeruginosa strain 1001 produces an esterase (EstA) that can hydrolyse the racemic methyl ester of β-acetylthioisobutyrate to produce the (D)-enantiomer, which serves as a precursor of captopril, a drug used for treatment of hypertension. We show here that PA2949 from P. aeruginosa PA01, a homologue of EstA, can efficiently be expressed in an enzymatically active form in E. coli. The enzyme is membrane-associated as demonstrated by cell fractionation studies. PA2949 was purified to homogeneity after solubilisation with the nonionic detergent, Triton X-100, and was shown to possess a conserved esterase catalytic triad consisting of Ser137-His258-Asp286. Our results should allow the development of an expression and purification strategy to produce this biotechnologically relevant esterase in a pure form with a high yield.

An effective approach for annotation of protein families with low sequence similarity and conserved motifs: identifying GDSL hydrolases across the plant kingdom

Background

The massive accumulation of protein sequences arising from the rapid development of high-throughput sequencing, coupled with automatic annotation, results in high levels of incorrect annotations. In this study, we describe an approach to decrease annotation errors of protein families characterized by low overall sequence similarity. The GDSL lipolytic family comprises proteins with multifunctional properties and high potential for pharmaceutical and industrial applications. The number of proteins assigned to this family has increased rapidly over the last few years. In particular, the natural abundance of GDSL enzymes reported recently in plants indicates that they could be a good source of novel GDSL enzymes. We noticed that a significant proportion of annotated sequences lack specific GDSL motif(s) or catalytic residue(s). Here, we applied motif-based sequence analyses to identify enzymes possessing conserved GDSL motifs in selected proteomes across the plant kingdom.

Results

Motif-based HMM scanning (Viterbi decoding-VD and posterior decoding-PD) and the here described PD/VD protocol were successfully applied on 12 selected plant proteomes to identify sequences with GDSL motifs. A significant number of identified GDSL sequences were novel. Moreover, our scanning approach successfully detected protein sequences lacking at least one of the essential motifs (171/820) annotated by Pfam profile search (PfamA) as GDSL. Based on these analyses we provide a curated list of GDSL enzymes from the selected plants. CLANS clustering and phylogenetic analysis helped us to gain a better insight into the evolutionary relationship of all identified GDSL sequences. Three novel GDSL subfamilies as well as unreported variations in GDSL motifs were discovered in this study. In addition, analyses of selected proteomes showed a remarkable expansion of GDSL enzymes in the lycophyte, Selaginella moellendorffii. Finally, we provide a general motif-HMM scanner which is easily accessible through the graphical user interface (http://compbio.math.hr/).

Conclusions

Our results show that scanning with a carefully parameterized motif-HMM is an effective approach for annotation of protein families with low sequence similarity and conserved motifs. The results of this study expand current knowledge and provide new insights into the evolution of the large GDSL-lipase family in land plants.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-016-0919-7) contains supplementary material, which is available to authorized users.

The Structure of a Novel Thermophilic Esterase from the Planctomycetes Species, Thermogutta terrifontis Reveals an Open Active Site Due to a Minimal 'Cap' Domain

A carboxyl esterase (TtEst2) has been identified in a novel thermophilic bacterium, Thermogutta terrifontis from the phylum Planctomycetes and has been cloned and over-expressed in Escherichia coli. The enzyme has been characterized biochemically and shown to have activity toward small p-nitrophenyl (pNP) carboxylic esters with optimal activity for pNP-acetate. The enzyme shows moderate thermostability retaining 75% activity after incubation for 30 min at 70°C. The crystal structures have been determined for the native TtEst2 and its complexes with the carboxylic acid products propionate, butyrate, and valerate. TtEst2 differs from most enzymes of the α/β-hydrolase family 3 as it lacks the majority of the ‘cap’ domain and its active site cavity is exposed to the solvent. The bound ligands have allowed the identification of the carboxyl pocket in the enzyme active site. Comparison of TtEst2 with structurally related enzymes has given insight into how differences in their substrate preference can be rationalized based upon the properties of their active site pockets.

Crystallization and preliminary X-ray analysis of a highly stable novel SGNH hydrolase (Est24) from Sinorhizobium meliloti

The SGNH hydrolase family includes enzymes that catalyze the hydrolysis of a broad range of substrates. Here, the crystallization and preliminary X-ray crystallographic studies of a novel SGNH hydrolase (Est24) from Sinorhizobium meliloti were performed. Recombinant Est24 protein containing an N-terminal His tag was expressed in Escherichia coli and purified to homogeneity. Est24 was then crystallized using a solution consisting of 0.2 M ammonium phosphate pH 4.6, 20% polyethylene glycol 3350. X-ray diffraction data were collected to a resolution of 1.45 Å with an R(merge) of 9.4%. The Est24 crystals belonged to space group C2, with unit-cell parameters a = 129.09, b = 88.63, c = 86.15 Å, α = 90.00, β = 114.30, γ = 90.00°. A molecular-replacement solution was obtained using the crystal structure of Mycobacterium smegmatis arylesterase as a template and structure refinement of Est24 is in progress.