Purification and characterization of an acetyl xylan esterase from Bacillus pumilus

Characterization of a GDS(L)-like hydrolase from Pleurotus sapidus with an unusual SGNH motif

The GDS(L)-like lipase from the Basidiomycota Pleurotus sapidus (PSA_Lip) was heterologously expressed using Trichoderma reesei with an activity of 350 U L-1. The isoelectric point of 5.0 was determined by isoelectric focusing. The novel PSA_Lip showed only 23.8-25.1%, 25.5%, 26.6% and 28.4% identity to the previously characterized GDSL-like enzymes phospholipase, plant lipase, acetylcholinesterase and acetylxylan esterase, from the carbohydrate esterase family 16, respectively. Therefore, the enzyme was purified from the culture supernatant and the catalytic properties and the substrate specificity of the enzyme were investigated using different assays to reveal its potential function. While no phospholipase, acetylcholinesterase and acetylxylan esterase activities were detected, studies on the hydrolysis of ferulic acid methyl ester (~ 8.3%) and feruloylated carbohydrate 5-O-transferuloyl-arabino-furanose (~ 0.8%) showed low conversions of these substrates. By investigating the hydrolytic activity towards p-nitrophenyl-(pNP)-esters with various chain-lengths, the highest activity was determined for medium chain-length pNP-octanoate at 65 °C and a pH value of 8, while almost no activity was detected for pNP-hexanoate. The enzyme is highly stable when stored at pH 10 and 4 °C for at least 7 days. Moreover, using consensus sequence analysis and homology modeling, we could demonstrate that the PSA_Lip does not contain the usual SGNH residues in the actives site, which are usually present in GDS(L)-like enzymes.

Biochemical characterization of an esterase from Thermobifida fusca YX with acetyl xylan esterase activity

BACKGROUND

Esterases (EC 3.1.1.X) are enzymes that catalyze the hydrolysis ester bonds. These enzymes have large potential for diverse applications in fine industries, particularly in pharmaceuticals, cosmetics, and bioethanol production.

METHODS AND RESULTS

In this study, a gene encoding an esterase from Thermobifida fusca YX (TfEst) was successfully cloned, and its product was overexpressed in Escherichia coli and purified using affinity chromatography. The TfEst kinetic assay revealed catalytic efficiencies of 0.58 s-1 mM-1, 1.09 s-1 mM-1, and 0.062 s-1 mM-1 against p-Nitrophenyl acetate, p-Nitrophenyl butyrate, and 1-naphthyl acetate substrates, respectively. Furthermore, TfEst also exhibited activity in a pH range from 6.0 to 10.0, with maximum activity at pH 8.0. The enzyme demonstrated a half-life of 20 min at 70 °C. Notably, TfEst displayed acetyl xylan esterase activity as evidenced by the acetylated xylan assay. The structural prediction of TfEst using AlphaFold indicated that has an α/β-hydrolase fold, which is consistent with other esterases.

CONCLUSIONS

The enzyme stability over a broad pH range and its activity at elevated temperatures make it an appealing candidate for industrial processes. Overall, TfEst emerges as a promising enzymatic tool with significant implications for the advancement of biotechnology and biofuels industries.

Recombinant acetylxylan esterase of Halalkalibacterium halodurans NAH-Egypt: molecular and biochemical study

Acetylxylan esterase plays a crucial role in xylan hydrolysis as the acetyl side-groups restrict endoxylanase action by stearic hindrance. In this study, an acetylxylan esterase (AXE-HAS10: 960 bp & 319 a.a) putative ORF from Halalkalibacterium halodurans NAH-Egypt was extensively studied through heterologous overexpression in Escherichia coli, biochemical characterization, and structural modeling. The AXE-HAS10 tertiary structure was predicted by the Local Meta Threading Server. AXE-HAS10 belongs to the carbohydrate esterase Family 7. Purified to homogeneity AXE-HAS10 showed specific activity (36.99 U/mg), fold purification (11.42), and molecular mass (41.39 kDa). AXE-HAS10 showed optimal pH (8.5) and temperature (40 oC). After 15 h of incubation at pH 7.0–9.0, AXE-HAS10 maintained 100% activity. After 120 min at 35 and 40 oC, the retained activity was 80 and 50%, respectively. At 10 mM Mn2+, Fe3+, K+, and Ca2+ after 30 min, retained activity was 329 ± 15, 212 ± 5.2, 123 ± 1.4, and 120 ± 3.0%, respectively. After 30 min of preincubation with triton x-100, SDS, and CTAB at 0.1% (v/v), the retained activity was 150 ± 19, 88 ± 4, and 82 ± 7%, respectively. At 6.0 M NaCl after 30 min, retained activity was 58%. A 1.44-fold enhancement of beechwood xylan hydrolysis was achieved by AXE-HAS10 and Penicillium chrysogenum DSM105774 β-xylanase concurrently. Present data underpins AXE-HAS10 as a promising AXE for industrial exploitation.

Sustainable Biosynthesis of Esterase Enzymes of Desired Characteristics of Catalysis for Pharmaceutical and Food Industry Employing Specific Strains of Microorganisms

Reactions catalysed by sustainably produced enzymes can contribute to the bioeconomy supporting several industries. Low-value compounds can be transformed into added-value products or high-resolution chemicals could be prepared in reactions catalysed by biocatalyst esterase enzymes. These enzymes can be synthesised by purposely isolated or genetically modified strains of microorganisms. Enzymes belonging to the hydrolase family catalyse the formation and hydrolysis of ester bonds to produce the desired esterified molecule. The synthesis of homo-chiral compounds can be accomplished either by chemical or biocatalytic processes, the latter being preferred with the use of microbial esterases. For varied applications, esterases with high stability and retained activity at lower and higher temperatures have been produced with strains isolated from extreme environments. For sustainable production of enzymes, higher productivity has been achieved by employing fast-growing Escherichia coli after incorporating plasmids of required characteristics from specific isolates. This is a review of the isolated and engineered strains used in the biosynthesis of esterase of the desired property, with the objective of a sustainable supply of enzymes, to produce products of industrial importance contributing to the economy.

Characterisation of a Novel Acetyl Xylan Esterase (BaAXE) Screened from the Gut Microbiota of the Common Black Slug (Arion ater)

Acetyl xylan esterases (AXEs) are enzymes capable of hydrolysing the acetyl bonds in acetylated xylan, allowing for enhanced activity of backbone-depolymerizing enzymes. Bioprospecting novel AXE is essential in designing enzyme cocktails with desired characteristics targeting the complete breakdown of lignocellulose. In this article, we report the characterisation of a novel AXE identified as Gene_id_40363 in the metagenomic library analysed from the gut microbiota of the common black slug. The conserved domain description was identified with an NCBI BLASTp search using the translated nucleotide sequence as a query. The activity of the recombinant enzyme was tested on various synthetic substrates and acetylated substrates. The protein sequence matched the conserved domain described as putative hydrolase and aligned closely to an uncharacterized esterase from Buttiauxella agrestis, hence the designation as BaAXE. BaAXE showed low sequence similarity among characterized CE family proteins with an available 3D structure. BaAXE was active on 4-nitrophenyl acetate, reporting a specific activity of 78.12 U/mg and a Km value of 0.43 mM. The enzyme showed optimal activity at 40 °C and pH 8 and showed high thermal stability, retaining over 40% activity after 2 h of incubation from 40 °C to 100 °C. BaAXE hydrolysed acetyl bonds, releasing acetic acid from acetylated xylan and β-D-glucose pentaacetate. BaAXE has great potential for biotechnological applications harnessing its unique characteristics. In addition, this proves the possibility of bioprospecting novel enzymes from understudied environments.

Pineapple Peel Extract as an Effective Substrate for Esterase Production from Bacillus subtilis E9

Esterase, belonging to hydrolase class of enzymes catalyzes the cleavage and formation of ester bonds. Esterase producing isolates E9 and E46, isolated from pineapple waste enriched soil were identified as Bacillus subtilis E9 and Bacillus sp. E46 respectively. Bacillus subtilis E9 with 10 U/mg esterase activity in basal media was further chosen for media optimization studies. Several factors including the effect of organic solvents and fruit peel extracts were studied by one factor at a time optimization method and statistical models. An enhanced enzyme production of 250.50 U/mg could be obtained under the optimal conditions of pH 6.5, incubation time 25 h and 1.8%v/v of acetone extract of pineapple peel. The four-stage purification improved the purity of the enzyme by 1.5-fold with 5.3% recovery and specific activity of 384 U/mg. The monomeric nature and the molecular weight (45 KDa) of the enzyme were determined by performing SDS PAGE and its activity was confirmed by zymogram analysis. The substrate specificity of the purified fraction exhibited a higher activity towards lower chain length esters, indicating the enzyme as esterase. The partially purified esterase showed an optimal temperature of 40 °C at an optimum pH of 7. K_m and V_max of the enzyme were 1.12 mM and 1.18 mM of released pNP · min^-1 respectively.

Extracellular alpha/beta-hydrolase from Paenibacillus species shares structural and functional homology to tobacco salicylic acid binding protein 2

An alpha/ beta hydrolase annotated as a putative salicylate esterase within the genome of a species of Paenibacillus previously identified from differential and selective growth on Kraft lignin was structurally and functionally characterised. Feruloyl esterases are key to the degradation of lignin in several bacterial species and although this activity was investigated, no such activity was observed. The crystal structure of the Paenibacillus esterase, here denoted as PnbE, was determined at 1.32 Å resolution, showing high similarity to Nicotiana tabacum salicylic acid binding protein 2 from the protein database. Structural similarities between these two structures across the core domains and key catalytic residues were observed, with superposition of catalytic residues giving an RMSD of 0.5 Å across equivalent Cα atoms. Conversely, the cap domains of PnbE and Nicotiana tabacum SABP2 showed greater divergence with decreased flexibility in the PnbE cap structure. Activity of PnbE as a putative methyl salicylate esterase was supported with binding studies showing affinity for salicylic acid and functional studies showing methyl salicylate esterase activity. We hypothesise that this activity could enrich Paenibacillus sp. within the rhizosphere by increasing salicylic acid concentrations within the soil.

Understanding the structural and functional properties of carbohydrate esterases with a special focus on hemicellulose deacetylating acetyl xylan esterases

Acetyl and methyl esterifications are two major naturally found substitutions in the plant cell-wall polysaccharides. The non-cellulosic plant cell-wall polysaccharides such as pectin and hemicellulose are differentially esterified by the O-acetyl and methyl groups to cease the action of various hydrolytic enzymes secreted by different fungi and bacterial species. Thus, microorganisms have emerged with a special class of enzymes known as carbohydrate esterases (CE). The CE catalyse O-de, N-deacetylation of acetylated saccharide residues (esters or amides, where sugars play the role of alcohol/amine/acid). Carbohydrate active enzyme (CAZy) database has classified CE into 16 classes, of which hemicellulose deacetylating CE were grouped into eight classes (CE-1 to CE-7 and CE-16). Various plant biomass degrading fungi and bacteria secretes acetyl xylan esterases (AcXE); however, these enzymes exhibit varied substrate specificities. AcXE and xylanases-coupled pretreatment methods exhibit significant applications, such as enhancing animal feedstock, baking industry, production of food additives, paper and pulp, xylitol production and biorefinery-based industries, respectively. Thus, understanding the structural and functional properties of acetyl xylan esterase will significantly aid in developing the efficient AcXE with wide range of industrial applications.

Structural Characterization and Directed Evolution of a Novel Acetyl Xylan Esterase Reveals Thermostability Determinants of the Carbohydrate Esterase 7 Family

A hot desert hypolith metagenomic DNA sequence data set was screened in silico for genes annotated as acetyl xylan esterases (AcXEs). One of the genes identified encoded an ∼36-kDa protein (Axe1NaM1). The synthesized gene was cloned and expressed, and the resulting protein was purified. NaM1 was optimally active at pH 8.5 and 30°C and functionally stable at salt concentrations of up to 5 M. The specific activity and catalytic efficiency were 488.9 U mg-1 and 3.26 × 106 M-1 s-1, respectively. The crystal structure of wild-type NaM1 was solved at a resolution of 2.03 Å, and a comparison with the structures and models of more thermostable carbohydrate esterase 7 (CE7) family enzymes and variants of NaM1 from a directed evolution experiment suggests that reduced side-chain volume of protein core residues is relevant to the thermal stability of NaM1. Surprisingly, a single point mutation (N96S) not only resulted in a simultaneous improvement in thermal stability and catalytic efficiency but also increased the acyl moiety substrate range of NaM1.IMPORTANCE AcXEs belong to nine carbohydrate esterase families (CE1 to CE7, CE12, and CE16), of which CE7 enzymes possess a unique and narrow specificity for acetylated substrates. All structurally characterized members of this family are moderately to highly thermostable. The crystal structure of a novel, mesophilic CE7 AcXE (Axe1NaM1), from a soil metagenome, provides a basis for comparisons with thermostable CE7 enzymes. Using error-prone PCR and site-directed mutagenesis, we enhanced both the stability and activity of the mesophilic AcXE. With comparative structural analyses, we have also identified possible thermal stability determinants. These are valuable for understanding the thermal stability of enzymes within this family and as a guide for future protein engineering of CE7 and other α/β hydrolase enzymes.

Role of an N-terminal extension in stability and catalytic activity of a hyperthermostable α/β hydrolase fold esterase

The carbohydrate esterase family 7 (CE7) enzymes catalyze the deacetylation of acetyl esters of a broad range of alcohols and is unique in its activity towards cephalosporin C. The CE7 fold contains a conserved N-terminal extension that distinguishes it from the canonical α/β hydrolase fold. The hexameric quaternary structure indicates that the N-terminus may affect activity and specificity by controlling access of substrates to the buried active sites via an entrance tunnel. In this context, we characterized the catalytic parameters, conformation and thermal stability of two truncation variants lacking four and ten residues of the N-terminal region of the hyperthermostable Thermotoga maritima CE7 acetyl esterase (TmAcE). The truncations did not affect the secondary structure or the fold but modulated the oligomerization dynamics. A modest increase was observed in substrate specificity for acetylated xylose compared with acetylated glucose. A drastic reduction of ~30-40°C in the optimum temperature for activity of the variants indicated lower thermal stability. The loss of hyperthermostability appears to be an indirect effect associated with an increase in the conformational flexibility of an otherwise rigid neighboring loop containing a catalytic triad residue. The results suggest that the N-terminal extension was evolutionarily selected to preserve the stability of the enzyme.

Esterase EstK from Pseudomonas putida mt-2: An enantioselective acetylesterase with activity for deacetylation of xylan and poly(vinylacetate)

An extracellular esterase gene estK was identified in Pseudomonas putida mt-2 and overexpressed at high levels in Escherichia coli. The recombinant EstK enzyme was purified and characterized kinetically against p-nitrophenyl ester and other aryl-alkyl ester substrates and found to be selective for hydrolysis of acetyl ester substrates with high activity for p-nitrophenyl acetate (k_cat 5.5 Sec^-1 , K_M 285 µM). Recombinant EstK was found to catalyze deacetylation of acetylated beech xylan, indicating a possible in vivo function for this enzyme, and partial deacetylation of a synthetic polymer (poly(vinylacetate)). EstK was found to catalyze enantioselective hydrolysis of racemic 1-phenylethyl acetate, generating 1R-phenylethanol with an enantiomeric excess of 80.4%.

Colorimetric Detection of Acetyl Xylan Esterase Activities

Colorimetric detection of reaction products is typically preferred for initial surveys of acetyl xylan esterase (AcXE) activity. This chapter will describe common colorimetric methods, and variations thereof, for measuring AcXE activities on commercial, synthesized, and natural substrates. Whereas assays using pNP-acetate, α-naphthyl acetate, and 4-methylumbelliferyl acetate (4MUA) are emphasized, common methods used to measure AcXE activity towards carbohydrate analogs (e.g., acetylated p-nitrophenyl β-D-xylopyranosides) and various acetylated xylans are also described. Strengths and limitations of the colorimetric assays are highlighted.

The production and characterization of a new active lipase from Acremonium alcalophilum using a plant bioreactor

BACKGROUND

Microorganisms are the most proficient decomposers in nature, using secreted enzymes in the hydrolysis of lignocellulose. As such, they present the most abundant source for discovery of new enzymes. Acremonium alcalophilum is the only known cellulolytic fungus that thrives in alkaline conditions and can be cultured readily in the laboratory. Its optimal conditions for growth are 30°C and pH 9.0-9.2. The genome sequence of Acremonium alcalophilum has revealed a large number of genes encoding biomass-degrading enzymes. Among these enzymes, lipases are interesting because of several industrial applications including biofuels, detergent, food processing and textile industries.

RESULTS

We identified a lipA gene in the genome sequence of Acremonium alcalophilum, encoding a protein with a predicted lipase domain with weak sequence identity to characterized enzymes. Unusually, the predicted lipase displays ≈ 30% amino acid sequence identity to both feruloyl esterase and lipase of Aspergillus niger. LipA, when transiently produced in Nicotiana benthamiana, accumulated to over 9% of total soluble protein. Plant-produced recombinant LipA is active towards p-nitrophenol esters of various carbon chain lengths with peak activity on medium-chain fatty acid (C8). The enzyme is also highly active on xylose tetra-acetate and oat spelt xylan. These results suggests that LipA is a novel lipolytic enzyme that possesses both lipase and acetylxylan esterase activity. We determined that LipA is a glycoprotein with pH and temperature optima at 8.0 and 40°C, respectively.

CONCLUSION

Besides being the first heterologous expression and characterization of a gene coding for a lipase from A. alcalophilum, this report shows that LipA is very versatile exhibiting both acetylxylan esterase and lipase activities potentially useful for diverse industry sectors, and that tobacco is a suitable bioreactor for producing fungal proteins.

Microbial carbohydrate esterases deacetylating plant polysaccharides

Several plant polysaccharides are partially esterified with acetic acid. One of the roles of this modification is protection of plant cell walls against invading microorganisms. Acetylation of glycosyl residues of polysaccharides prevents hydrolysis of their glycosidic linkages by the corresponding glycoside hydrolases. In this way the acetylation also represents an obstacle of enzymatic saccharification of plant hemicelluloses to fermentable sugars which appears to be a hot topic of current research. We can eliminate this obstacle by alkaline extraction or pretreatment leading to saponification of ester linkages. However, this task has been accomplished in a different way in the nature. The acetyl groups became targets of microbial carbohydrate esterases that evolved to overcome the complexity of the plant cell walls and that cooperate with glycoside hydrolases in plant polysaccharide degradation. This article concentrates on enzymes deacetylating plant hemicelluloses excluding pectin. They are currently grouped in at least 8 families, specifically in CE families 1-7 and 16, originally assigned as acetylxylan esterases, the enzymes acting on hardwood acetyl glucuronoxylan and its fragments generated by endo-β-1,4-xylanases. There are esterases deacetylating softwood galactoglucomannan, but they have not been classified yet. The enzymes present in CE families 1-7 differ in structure and substrate and positional specificity. There are families behaving as endo-type and exo-type deacetylates, i.e. esterases deacetylating internal sugar residues of partially acetylated polysaccharides and also esterases deacetylating non-reducing end sugar residues in oligosaccharides. With one exception, the enzymes of all mentioned CE families belong to serine type esterases. CE family 4 harbors enzymes that are metal-dependent aspartic esterases. Three-dimensional structures have been solved for members of the first seven CE families, however, there is still insufficient knowledge about their substrate specificity and real physiological role. Current knowledge on catalytic properties of the selected families of CEs is summarized in this review. Some of the families are emerging also as new biocatalysts for regioselective acylation and deacylation of carbohydrates.

Hyperthermostable acetyl xylan esterase

An esterase which is encoded within a Thermotoga maritima chromosomal gene cluster for xylan degradation and utilization was characterized after heterologous expression of the corresponding gene in Escherichia coli and purification of the enzyme. The enzyme, designated AxeA, shares amino acid sequence similarity and its broad substrate specificity with the acetyl xylan esterase from Bacillus pumilus, the cephalosporin C deacetylase from Bacillus subtilis, and other (putative) esterases, allowing its classification as a member of carbohydrate esterase family 7. The recombinant enzyme displayed activity with p‐nitrophenyl‐acetate as well as with various acetylated sugar substrates such as glucose penta‐acetate, acetylated oat spelts xylan and DMSO (dimethyl sulfoxide)‐extracted beechwood xylan, and with cephalosporin C. Thermotoga maritimaAxeA represents the most thermostable acetyl xylan esterase known to date. In a 10 min assay at its optimum pH of 6.5 the enzyme's activity peaked at 90°C. The inactivation half‐life of AxeA at a protein concentration of 0.3 µg µl⁻¹ in the absence of substrate was about 13 h at 98°C and about 67 h at 90°C. Differential scanning calorimetry analysis of the thermal stability of AxeA corroborated its extreme heat resistance. A multi‐phasic unfolding behaviour was found, with two apparent exothermic peaks at approximately 100–104°C and 107.5°C. In accordance with the crystal structure, gel filtration analysis at ambient temperature revealed that the enzyme has as a homohexameric oligomerization state, but a dimeric form was also found.

Purification and partial characterization of acetic acid esterase from malted finger millet (Eleusine coracana, Indaf-15)

Acetic acid esterase (EC 3.1.1.6) cleaves the acetyl groups substituted at O-2/O-3 of the xylan backbone of arabinoxylans and is known to modulate their functional properties. To date, this enzyme from cereals has not received much attention. In the present study, acetic acid esterase from 72 h ragi malt was isolated and purified to apparent homogeneity by a four-step purification, i.e., ammonium sulfate precipitation, DEAE-cellulose, Sephacryl S-200, and phenyl-Sepharose column chromatography, with a recovery of 0.36% and a fold purification of 34. The products liberated from alpha-NA and PNPA by the action of purified ragi acetic acid esterase were authenticated by ESI-MS and 1H NMR. The pH and temperature optima of the enzyme were found to be 7.5 and 45 degrees C, respectively. The enzyme is stable in the pH range of 6.0-9.0 and temperature range of 30-40 degrees C. The activation energy of the enzymatic reaction was found to be 7.29 kJ mol-1. The apparent Km and Vmax of the purified acetic acid esterase for alpha-NA were 0.04 microM and 0.175 microM min-1 mL-1, respectively. The molecular weight of the native enzyme was found to be 79.4 kDa by GPC whereas the denatured enzyme was found to be 19.7 kDa on SDS, indicating it to be a tetramer. EDTA, citric acid, and metal ions such as Fe+3 and Cu+2 increased the activity while Ni+2, Ca+2, Co+2, Ba+2, Mg+2, Mn+2, Zn+2, and Al+3 reduced the activity. Group-specific reagents such as eserine and PCMB at 25 mM concentration completely inhibited the enzyme while iodoacetamide did not have any effect. Eserine was found to be a competitive inhibitor.

Diversity of plant cell wall esterases in thermophilic and thermotolerant fungi

Fourteen thermophilic and thermotolerant fungal strains isolated from composting soils produced plant cell wall-acting esterases in a medium containing corn cobs and oat spelt xylan. The concentrated and dialyzed protein extracts of these fungi were fractionated using isoelectric-focusing, gels sliced and eluted protein in each slice was assayed for esterase activity against p-nitrophenyl acetate. A total of 84 esterases detected on the basis of pI were found to show distinct preferential substrate specificities towards p-nitrophenyl acetate, p-nitrophenyl ferulate and p-nitrophenyl butyrate, and were putatively classified as acetyl esterases and esterases types I and II. None of the esterases were active against p-nitrophenyl myristate. In addition, these esterases were characterized as acid, neutral or alkaline active.

Isolation and biochemical characterization of two novel metagenome-derived esterases

The metagenomes of uncultured microbial communities are rich sources for novel biocatalysts. In this study, esterase EstA3 was derived from a drinking water metagenome, and esterase EstCE1 was derived from a soil metagenome. Both esterases are approximately 380 amino acids in size and show similarity to beta-lactamases, indicating that they belong to family VIII of the lipases/esterases. EstA3 had a temperature optimum at 50 degrees C and a pH optimum at pH 9.0. It was remarkably active and very stable in the presence of solvents and over a wide temperature and pH range. It is active in a multimeric form and displayed a high level of activity against a wide range of substrates including one secondary ester, 7-[3-octylcarboxy-(3-hydroxy-3-methyl-butyloxy)]-coumarin, which is normally unreactive. EstCE1 was active in the monomeric form and had a temperature optimum at 47 degrees C and a pH optimum at pH 10. It exhibited the same level of stability as EstA3 over wide temperature and pH ranges and in the presence of dimethyl sulfoxide, isopropanol, and methanol. EstCE1 was highly enantioselective for (+)-menthylacetate. These enzymes display remarkable characteristics that cannot be related to the original environment from which they were derived. The high level of stability of these enzymes together with their unique substrate specificities make them highly useful for biotechnological applications.

An Aspergillus oryzae acetyl xylan esterase: Molecular cloning and characteristics of recombinant enzyme expressed in Pichia pastoris

We screened 20,000 clones of an expressed sequence tag (EST) library from Aspergillus oryzae (http://www.nrib.go.jp/ken/EST/db/index.html) and obtained one cDNA clone encoding a protein with similarity to fungal acetyl xylan esterase. We also cloned the corresponding gene, designated as Aoaxe, from the genomic DNA. The deduced amino acid sequence consisted of a putative signal peptide of 31-amino acids and a mature protein of 276-amino acids. We engineered Aoaxe for heterologous expression in P. pastoris. Recombinant AoAXE (rAoAXE) was secreted by the aid of fused alpha-factor secretion signal peptide and accumulated as an active enzyme in the culture medium to a final level of 190 mg/l after 5 days. Purified rAoAXEA before and after treatment with endoglycosidase H migrated by SDS-PAGE with a molecular mass of 31 and 30 kDa, respectively. Purified rAoAXE displayed the greatest hydrolytic activity toward alpha-naphthylacetate (C2), lower activity toward alpha-naphthylpropionate (C3) and no detectable activity toward acyl-chain substrates containing four or more carbon atoms. The recombinant enzyme catalyzed the release of acetic acid from birchwood xylan. No activity was detectable using methyl esters of ferulic, caffeic or sinapic acids. rAoAXE was thermolabile in comparison to other AXEs from Aspergillus.

Heterologous expression, purification, crystallization, X-ray analysis and phasing of the acetyl xylan esterase from Bacillus pumilus

Bacillus pumilus PS213 acetyl xylan esterase (AXE) acts as an accessory enzyme in the plant cell wall hemicellulose biodegradation pathway. It belongs to the carbohydrate esterase family 7 and hydrolyses the ester linkages of the acetyl groups in position 2 and/or 3 of the xylose moieties of the acetylated xylan fragments from hardwood. The enzyme displays activity towards a broad range of acetylated compounds including the antibiotic cephalosporin-C. In this study we report the heterologous expression, purification, physicochemical characterization and crystallization of the recombinant B. pumilus AXE. Remarkable improvement of the crystal quality was achieved by setting up crystallization conditions, at first established using the hanging drop vapor diffusion method, in a micro-batch experiment. Rod-like diffraction quality crystals were obtained using 10% PEG 6000, 0.1 M MES pH 6.0 and a wide range of LiCl concentrations (0.2-1.0 M) as precipitant agent. Two different crystal forms, both belonging to space group P2(1), were characterized, diffracting X-rays to 2.5 and 1.9 angstrom resolution. Successful molecular replacement showed 12 molecules in the asymmetric unit of either crystal forms that are arranged as two doughnut-like hexamers, each one encompassing a local 32 symmetry. A catalytic inactive mutant Ser181Ala of B. pumilus AXE was also engineered, expressed, purified and crystallized for functional and structural studies.

Multifunctional xylooligosaccharide/cephalosporin C deacetylase revealed by the hexameric structure of the Bacillus subtilis enzyme at 1.9A resolution

Esterases and deacetylases active on carbohydrate ligands have been classified into 14 families based upon amino acid sequence similarities. Enzymes from carbohydrate esterase family seven (CE-7) are unusual in that they display activity towards both acetylated xylooligosaccharides and the antibiotic, cephalosporin C. The 1.9A structure of the multifunctional CE-7 esterase (hereinafter CAH) from Bacillus subtilis 168 reveals a classical alpha/beta hydrolase fold encased within a 32 hexamer. This is the first example of a hexameric alpha/beta hydrolase and is further evidence of the versatility of this particular fold, which is used in a wide variety of biological contexts. A narrow entrance tunnel leads to the centre of the molecule, where the six active-centre catalytic triads point towards the tunnel interior and thus are sequestered away from cytoplasmic contents. By analogy to self-compartmentalising proteases, the tunnel entrance may function to hinder access of large substrates to the poly-specific active centre. This would explain the observation that the enzyme is active on a variety of small, acetylated molecules. The structure of an active site mutant in complex with the reaction product, acetate, reveals details of the putative oxyanion binding site, and suggests that substrates bind predominantly through non-specific contacts with protein hydrophobic residues. Protein residues involved in catalysis are tethered by interactions with protein excursions from the canonical alpha/beta hydrolase fold. These excursions also mediate quaternary structure maintenance, so it would appear that catalytic competence is only achieved on protein multimerisation. We suggest that the acetyl xylan esterase (EC 3.1.1.72) and cephalosporin C deacetylase (EC 3.1.1.41) enzymes of the CE-7 family represent a single class of proteins with a multifunctional deacetylase activity against a range of small substrates.

A thermostable alpha-arabinofuranosidase from xylanolytic Bacillus pumilus: purification and characterisation

Bacillus pumilus PS213 secretes an alpha-L-arabinofuranosidase (AF) when grown in the presence of arabinogalactan or oat meal. The enzyme has been purified to homogeneity and characterised. Its molecular mass, as determined by gel filtration, is 220 kDa, while sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) showed a single band of approximately 60 kDa. According to the result of the mass spectrometry analysis showing a molecular mass of 56 kDa, the enzyme should be a homotetramer. The isoelectric point was found to be 5.2, the enzyme activity was optimal at 55 degrees C and pH 7.0. The enzyme retained 80% of its activity after 2 h at 65 degrees C and lost 50% of activity at 75 degrees C after 135 min. The Michaelis constant K(m) and V(max) for p-nitrophenylarabinofuranoside at 37 degrees C were 1.7 mM and 52.9 U mg(-1), respectively. N-terminal sequence analysis and internal peptide fragments showed homology with glycosyl hydrolases of family 51.

The acetyl xylan esterase of Bacillus pumilus belongs to a family of esterases with broad substrate specificity

The Bacillus pumilus gene encoding acetyl xylan esterase (axe) was identified and characterized. The axe gene was expressed and the recombinant enzyme produced in Escherichia coli was purified and characterized. The recombinant enzyme displayed similar properties to the acetyl xylan esterase (AXE) purified from B. pumilus. The AXE primary structure was 76% identical to the cephalosporin C deacetylase of B. subtilis, and 40% to two recently identified AXEs from Thermoanaerobacterium and Thermotoga maritima. These four proteins are of similar size and represent a new family of esterases having a broad substrate specificity. The recombinant AXE was demonstrated to have activity on several acetylated substrates, including on cephalosporin C.

Purification and characterization of acetyl esterase from Candida guilliermondii

An extracellular acetyl esterase (EC 3.1.1.6) from Candida guilliermondii NRRL Y-17257 was purified to homogeneity by acetone precipitation and QAE sepharose anion-exchange chromatography. The enzyme was a monomer with an apparent molecular weight of 67 kDa and a pI of 7.6. It had maximum activity at pH 7.5 and at 50-60 degrees C. It was relatively stable over a pH range of 5.8-8.0 and exhibited thermal stability up to 60 degrees C. The Km and Vmax values on alpha-naphthylacetate were 2.63 mM and 213.3 micromol alpha- naphthol min-1 mg-1 protein, respectively.

Purification and properties of an esterase from the yeast Saccharomyces cerevisiae and identification of the encoding gene

We purified an intracellular esterase that can function as an S-formylglutathione hydrolase from the yeast Saccharomyces cerevisiae. Its molecular mass was 40 kDa, as determined by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The isoelectric point was 5.0 by isoelectric focusing. The enzyme activity was optimal at 50 degrees C and pH 7.0. The corresponding gene, YJLO68C, was identified by its N-terminal amino acid sequence and is not essential for cell viability. Null mutants have reduced esterase activities and grow slowly in the presence of formaldehyde. This enzyme may be involved in the detoxification of formaldehyde, which can be metabolized to S-formylglutathione by S. cerevisiae.