A cold-adapted esterase from psychrotrophic Pseudoalteromas sp. strain 643A

Discovery, characterization and mechanism of a Microbacterium esterase for key d-biotin chiral intermediate synthesis

Esterases are crucial biocatalysts in chiral compound synthesis. Herein, a novel esterase EstSIT01 belonging to family V was identified from Microbacterium chocolatum SIT101 through genome mining and phylogenetic analysis. EstSIT01 demonstrated remarkable efficiency in asymmetrically hydrolyzing meso-dimethyl ester [Dimethyl cis-1,3-Dibenzyl-2-imidazolidine-4,5-dicarboxyate], producing over 99% yield and 99% enantiomeric excess (e.e.) for (4S, 5R)-monomethyl ester, a crucial chiral intermediate during the synthesis of d-biotin. Notably, the recombinant E. coli expressing EstSIT01 exhibited over 40-fold higher activity than that of the wild strain. EstSIT01 displays a preference for short-chain p-NP esters. The optimal temperature and pH were 45 °C and 10.0, with Km and kcat values of 0.147 mmol/L and 5.808 s- 1, respectively. Molecular docking and MD simulations suggest that the high stereoselectivity for meso-diester may attribute to the narrow entrance tunnel and unique binding pocket structure. Collectively, EstSIT01 holds great potential for preparing chiral carboxylic acids and esters.

A Novel Thermo-Alkaline Stable GDSL/SGNH Esterase with Broad Substrate Specificity from a Deep-Sea Pseudomonas sp

Marine environments harbor a plethora of microorganisms that represent a valuable source of new biomolecules of biotechnological interest. In particular, enzymes from marine bacteria exhibit unique properties due to their high catalytic activity under various stressful and fluctuating conditions, such as temperature, pH, and salinity, fluctuations which are common during several industrial processes. In this study, we report a new esterase (EstGoM) from a marine Pseudomonas sp. isolated at a depth of 1000 m in the Gulf of Mexico. Bioinformatic analyses revealed that EstGoM is an autotransporter esterase (type Va) and belongs to the lipolytic family II, forming a new subgroup. The purified recombinant EstGoM, with a molecular mass of 67.4 kDa, showed the highest hydrolytic activity with p-nitrophenyl octanoate (p-NP C8), although it was also active against p-NP C4, C5, C10, and C12. The optimum pH and temperature for EstGoM were 9 and 60 °C, respectively, but it retained more than 50% of its activity over the pH range of 7-11 and temperature range of 10-75 °C. In addition, EstGoM was tolerant of up to 1 M NaCl and resistant to the presence of several metal ions, detergents, and chemical reagents, such as EDTA and β-mercaptoethanol. The enzymatic properties of EstGoM make it a potential candidate for several industrial applications.

Comprehensive insights on environmental adaptation strategies in Antarctic bacteria and biotechnological applications of cold adapted molecules

Climate change and the induced environmental disturbances is one of the major threats that have a strong impact on bacterial communities in the Antarctic environment. To cope with the persistent extreme environment and inhospitable conditions, psychrophilic bacteria are thriving and displaying striking adaptive characteristics towards severe external factors including freezing temperature, sea ice, high radiation and salinity which indicates their potential in regulating climate change's environmental impacts. The review illustrates the different adaptation strategies of Antarctic microbes to changing climate factors at the structural, physiological and molecular level. Moreover, we discuss the recent developments in "omics" approaches to reveal polar "blackbox" of psychrophiles in order to gain a comprehensive picture of bacterial communities. The psychrophilic bacteria synthesize distinctive cold-adapted enzymes and molecules that have many more industrial applications than mesophilic ones in biotechnological industries. Hence, the review also emphasizes on the biotechnological potential of psychrophilic enzymes in different sectors and suggests the machine learning approach to study cold-adapted bacteria and engineering the industrially important enzymes for sustainable bioeconomy.

Screening, identification, and characterization of lipase-producing halotolerant Bacillus altitudinis Ant19 from Antarctic soil

Potent lipase-producing and halotolerant Bacillus altitudinis Ant19 strain was screened and isolated from Antarctic soil. The isolate showed broad-range lipase activity against different lipid substrates. Presence of lipase activity was confirmed by PCR amplification and sequencing of the lipase gene from Ant19. The study attempted to establish the use of crude extracellular lipase extract as cheap alternative to purified enzyme by characterizing the crude lipase activity and testing it in certain practical applications. Crude lipase extract from Ant19 showed high stability at 5-28 ℃ (> 97%), while lipase activity was noted in a wide temperature range of 20-60 ℃ (> 69%), with optimum activity at 40 ℃ (117.6%). The optimum lipolytic activity was noted at pH 8 with good activity and stability in alkaline conditions (pH 7-10). Moreover, the lipase activity was substantially stable in various solvents, commercial detergents, and surfactants. It retained 97.4% activity in 1% solution of commercial Nirma detergent. Besides, it was non-regiospecific, and active against substrates having different fatty acid chain lengths with preference for shorter chain length. Further, the crude lipase enhanced the oil stain removal efficiency of commercial detergent from 52 to 77.9%, while 66% oil stain was removed using crude lipase alone. Immobilization process improved the storage stability of crude lipase for 90 days. In our knowledge, it is the first study on characterization of lipase activity from B. altitudinis, which has promising applications in various fields.

Molecular study on recombinant cold-adapted, detergent- and alkali stable esterase (EstRag) from Lysinibacillus sp.: a member of family VI

Cold-adapted esterases have potential industrial applications. To fulfil the global continuous demand for these enzymes, a cold-adapted esterase member of family VI from Lysinibacillus sp. YS11 was cloned on pET-28b (+) vector and expressed in E. coli BL21(DE3) Rosetta cells for the first time. The open reading frame (654 bp: GenBank MT120818.1) encodes a polypeptide (designated EstRag: 217 amino acid residues). EstRag amino acid sequence has conserved esterase signature motifs: pentapeptide (GFSQG) and catalytic triad Ser¹¹⁰-Asp¹⁶³-His¹⁹⁴. EstRag 3D predicted model, built with LOMETS3 program, showed closest structural similarity to PDB 1AUO_A (esterase: Pseudomonas fluorescens); TM-align score program inferences. Purified EstRag to 9.28-fold, using Ni²⁺affinity agarose matrix, showed a single protein band (25 kDa) on SDS-PAGE, Km (0.031 mM) and Kcat/Km (657.7 s⁻¹ mM⁻¹) on p-NP-C2. Temperature and pH optima of EstRag were 35 °C and 8.0, respectively. EstRag was fully stable at 5–30 °C for 120 min and at pH(s) 8.0–10.0 after 24 h. EstRag activity (391.46 ± 0.009%) was impressively enhanced after 30 min preincubation with 5 mM Cu²⁺. EstRag retained full stability after 30 min pre-incubation with 0.1%(v/v) SDS, Triton X-100, and Tween-80. EstRag promising characteristics motivate performing guided evolution and industrial applications prospective studies.

Molecular characterization of lipase from a psychrotrophic bacterium Pseudomonas sp. CRBC14

Lipases from Pseudomonas species are particularly useful due to their broader biocatalytic applications and temperature activity. In this study, we amplified the gene encoding wild-type cold-active lipase from the genome of psychrotrophic bacterium isolated from the Himalayan glacier. The isolated CRBC14 strain was identified as Pseudomonas sp. based on the 16S rRNA gene sequence. Lipase activity was determined by observing the hydrolysis zone on nutrient agar containing tributyrin (1%, v/v). The sequence analysis of cold-active lipase revealed a protein of 611 amino acids with a calculated molecular mass of 63.71 kDa. The three-dimensional structure of this lipase was generated through template-supported modeling. Distinct techniques stamped the model quality, following which the binding free energies of tributyrin and oleic acid in the complex state with this enzymatic protein were predicted through molecular mechanics generalized born surface area (MMGBSA). A relative comparison of binding free energy values of these substrates indicated tributyrin's comparatively higher binding propensity towards the lipase. Using molecular docking, we evaluated the binding activity of cold-active lipase against tributyrin and oleic acid. Our docking analysis revealed that the lipase had a higher affinity for tributyrin than oleic acid, as evidenced by our measurement of the hydrolysis zone on two media plates. This study will help to understand the bacterial diversity of unexplored Himalayan glaciers and the possible application of their cold-adapted enzymes.

Production of extracellular lipase from psychrotrophic bacterium Oceanisphaera sp. RSAP17 isolated from arctic soil

Cold-active extracellular lipases produced by different psychrotrophs are important for various industrial applications. We have isolated a Gram-negative, rod-shaped, aerobe, non-pigment producing psychrotrophic bacterial strain RSAP17 (MTCC 12991, MCC 4275) from the unexplored Arctic soil sample of NyAlesund, Svalbard, Norway (78° 55″ N, 11° 54″ E). The detailed morphological, biochemical, and molecular characteristics were investigated to characterize the isolate RSAP17. Analyses of the 16S rDNA sequence of strain RSAP17 (Accession no. MK391379) shows the closest match with Oceanisphaera marina YM319^T (99.45%) and Oceanisphaera sediminis TW92 JCM 17329^T (97.40%). The isolate is capable of producing extracellular lipase but not amylase, cellulase or urease. The optimal parameters for lipase production have been found in tributyrin based (10 mL/L) agar media supplemented with 3% (w/v) NaCl after 2-3 days of incubation at 20-22 °C temperature and pH 9 at shaking condition. We have purified the extracellular lipase from the RSAP17 grown culture supernatant through 75% ammonium sulfate precipitation followed by dialysis and DEAE cellulose column chromatography. The invitro lipolytic activity of the purified lipase enzymes has been done through zymogram analysis. The molecular weight found for the lipase is 103.8 kD. The optimal activity of the purified lipase has been found at 25 °C and pH 9. MALDI-TOF-MS study of the purified lipase showed the highest match with the sequence of prolipoprotein diacylglyceryl transferase with 44% sequence coverage. Further study on large-scale production, substrate utilization and enzymatic kinetics of this lipase could unravel its possibility in future biotechnological applications.

Purification and refolding protocol for cold-active recombinant esterase AaSGNH1 from Aphanizomenon flos-aquae expressed as insoluble inclusion bodies

Microbial esterases are a highly desirable tool for numerous biosynthetic and biotechnological applications requiring ester bond cleavage. Once identified, microbial esterases are often produced recombinantly in Escherichia coli to enhance yield and ease of purification. In this study a polyhistidine-tagged SGNH esterase gene (AaSGNH1), originating from the cyanobacterium Aphanizomenon flos-aquae, was cloned into an over-expression plasmid and expressed in BL21(DE3) cells. The recombinant esterase enzyme was produced as inactive inclusion bodies which were insoluble in 8 M urea but readily solubilized by the detergent Empigen BB^®. Crucially, the procurement of active enzyme required controlled removal of detergent during column chromatography and dialysis steps. The refolded esterase was characterized with respect to its ability to catalyze the cleavage of p-nitrophenol esters of different chain lengths (C2, C8, C16). In addition, the temperature and pH optima were determined and it was found that the enzyme was most active at low temperatures (5-15 °C) and under alkaline conditions (pH 8-10). It was found that the kinetic properties of AaSGNH1 were remarkably similar to other SGNH esterases described thereby validating that the protein was effectively refolded. Overall, this study provides a simple strategy for isolating cold-active recombinant esterase enzyme when expressed as inclusion bodies.

Marine Bacterial Esterases: Emerging Biocatalysts for Industrial Applications

The marine ecosystem has been known to be a significant source of novel enzymes. Esterase enzymes (EC 3.1.1.1) represent a diverse group of hydrolases that catalyze the cleavage and formation of ester bonds. Although esterases are widely distributed among marine organisms, only microbial esterases are of paramount industrial importance. This article discusses the importance of marine microbial esterases, their biochemical and kinetic properties, and their stability under extreme conditions. Since culture-dependent techniques provide limited insights into microbial diversity of the marine ecosystem, therefore, genomics and metagenomics approaches have widely been adopted in search of novel esterases. Additionally, the article also explains industrial applications of marine bacterial esterases particularly for the synthesis of optically pure substances, the preparation of enantiomerically pure drugs, the degradation of human-made plastics and organophosphorus compounds, degradation of the lipophilic components of the ink, and production of short-chain flavor esters.

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.

Enzymes from Marine Polar Regions and Their Biotechnological Applications

The microorganisms that evolved at low temperatures express cold-adapted enzymes endowed with unique catalytic properties in comparison to their mesophilic homologues, i.e., higher catalytic efficiency, improved flexibility, and lower thermal stability. Cold environments are therefore an attractive research area for the discovery of enzymes to be used for investigational and industrial applications in which such properties are desirable. In this work, we will review the literature on cold-adapted enzymes specifically focusing on those discovered in the bioprospecting of polar marine environments, so far largely neglected because of their limited accessibility. We will discuss their existing or proposed biotechnological applications within the framework of the more general applications of cold-adapted enzymes.

Characterization of an acetyl xylan esterase from the marine bacterium Ochrovirga pacifica and its synergism with xylanase on beechwood xylan

BACKGROUND

Acetyl xylan esterase plays an important role in the complete enzymatic hydrolysis of lignocellulosic materials. It hydrolyzes the ester linkages of acetic acid in xylan and supports and enhances the activity of xylanase. This study was conducted to identify and overexpress the acetyl xylan esterase (AXE) gene revealed by the genomic sequencing of the marine bacterium Ochrovirga pacifica.

RESULTS

The AXE gene has an 864-bp open reading frame that encodes 287 aa and consists of an AXE domain from aa 60 to 274. Gene was cloned to pET-16b vector and expressed the recombinant AXE (rAXE) in Escherichia coli BL21 (DE3). The predicted molecular mass was 31.75 kDa. The maximum specific activity (40.08 U/mg) was recorded at the optimal temperature and pH which were 50 °C and pH 8.0, respectively. The thermal stability assay showed that AXE maintains its residual activity almost constantly throughout and after incubation at 45 °C for 120 min. The synergism of AXE with xylanase on beechwood xylan, increased the relative activity 1.41-fold.

CONCLUSION

Resulted higher relative activity of rAXE with commercially available xylanase on beechwood xylan showed its potential for the use of rAXE in industrial purposes as a de-esterification enzyme to hydrolyze xylan and hemicellulose-like complex substrates.

The art of adapting to extreme environments: The model system Pseudoalteromonas

Extremophilic microbes have adapted to thrive in ecological niches characterized by harsh chemical/physical conditions such as, for example, very low/high temperature. Living organisms inhabiting these environments have developed peculiar mechanisms to cope with extreme conditions, in such a way that they mark the chemical-physical boundaries of life on Earth. Studying such mechanisms is stimulating from a basic research viewpoint and because of biotechnological applications. Pseudoalteromonas species are a group of marine gamma-proteobacteria frequently isolated from a range of extreme environments, including cold habitats and deep-sea sediments. Since deep-sea floors constitute almost 60% of the Earth's surface and cold temperatures represent the most common of the extreme conditions, the genus Pseudoalteromonas can be considered one of the most important model systems for studying microbial adaptation. Particularly, among all Pseudoalteromonas representatives, P. haloplanktis TAC125 has recently gained a central role. This bacterium was isolated from seawater sampled along the Antarctic ice-shell and is considered one of the model organisms of cold-adapted bacteria. It is capable of thriving in a wide temperature range and it has been suggested as an alternative host for the soluble overproduction of heterologous proteins, given its ability to rapidly multiply at low temperatures. In this review, we will present an overview of the recent advances in the characterization of Pseudoalteromonas strains and, more importantly, in the understanding of their evolutionary and chemical-physical strategies to face such a broad array of extreme conditions. A particular attention will be given to systems-biology approaches in the study of the above-mentioned topics, as genome-scale datasets (e.g. genomics, proteomics, phenomics) are beginning to expand for this group of organisms. In this context, a specific section dedicated to P. haloplanktis TAC125 will be presented to address the recent efforts in the elucidation of the metabolic rewiring of the organisms in its natural environment (Antarctica).

The first description of a hormone-sensitive lipase from a basidiomycete: Structural insights and biochemical characterization revealed Bjerkandera adusta BaEstB as a novel esterase

The heterologous expression and characterization of a Hormone-Sensitive Lipases (HSL) esterase (BaEstB) from the Basidiomycete fungus Bjerkandera adusta is reported for the first time. According to structural analysis, amino acid similarities and conservation of particular motifs, it was established that this enzyme belongs to the (HSL) family. The cDNA sequence consisted of 969 nucleotides, while the gene comprised 1133, including three introns of 57, 50, and 57 nucleotides. Through three-dimensional modeling and phylogenetic analysis, we conclude that BaEstB is an ortholog of the previously described RmEstB-HSL from the phylogenetically distant fungus Rhizomucor miehei. The purified BaEstB was characterized in terms of its specificity for the hydrolysis of different acyl substrates confirming its low lipolytic activity and a noticeable esterase activity. The biochemical characterization of BaEstB, the DLS analysis and the kinetic parameters determination revealed this enzyme as a true esterase, preferentially found in a dimeric state, displaying activity under alkaline conditions and relative low temperature (pH = 10, 20°C). Our data suggest that BaEstB is more active on substrates with short acyl chains and bulky aromatic moieties. Phylogenetic data allow us to suggest that a number of fungal hypothetical proteins could belong to the HSL family.

Parasites and Diseases

The Antarctic krill Euphausia superba is among the most studied species of the Order Euphausiacea in biological and ecological aspects; however, reports of their parasites and diseases are relatively scarce. A worldwide overview of all parasites known for 48 out 86 extant euphausiid species includes 17 distinct types of epibionts, pathogens, parasites, and parasitoids. So far, only seven of them have been reported interacting with E. superba [epibionts: exuviotrophic ciliates (Foettingeriidae) and microplanktophagous ciliates (Suctoridae, Ephelota), pathogens: chitinoclastic bacteria and fungi; and trophically transmitted endoparasites: Apicomplexans (Gregarinidae, Cephaloidophora), nematode infecting krill’s eggs (under laboratory conditions), and histophagous parasites: Apostomatida ciliates of the family Pseudocollinidae]. The epibionts have interspecific associations that strongly depend on the krill’s moult cycle, discarding them at each moulting event. Their colonization and intensity show a remarkable synchronization with the krill moulting process at individual, school, and population levels. The social and sometimes highly dense swarms and schools of E. superba, its keystone trophic function (both as voracious predator and as prey to multiple predators) should make it a critical vector for trophically transmitted parasites in the food web. However, E. superba interacts with a relatively low diversity of epibionts, pathogens, and parasites, in comparison with parasite diversity known for relatively well-studied temperate (Meganyctiphanes norvegica, Euphausia pacifica) and subtropical (Nyctiphanes simplex) euphausiid species. The apparently low parasite diversity of E. superba is likely associated with its Antarctic zoogeographic pattern; where, parasites have not invaded the Antarctic krill with the same evolutionary success as have occurred with other euphausiid species from tropical, subtropical, temperate, and even Arctic ecosystems.

A novel thermoalkalostable esterase from Acidicaldus sp. strain USBA-GBX-499 with enantioselectivity isolated from an acidic hot springs of Colombian Andes

Several thermo- and mesoacidophilic bacterial strains that revealed high lipolytic activity were isolated from water samples derived from acidic hot springs in Los Nevados National Natural Park (Colombia). A novel lipolytic enzyme named 499EST was obtained from the thermoacidophilic alpha-Proteobacterium Acidicaldus USBA-GBX-499. The gene estA encoded a 313-amino-acid protein named 499EST. The deduced amino acid sequence showed the highest identity (58 %) with a putative α/β hydrolase from Acidiphilium sp. (ZP_08632277.1). Sequence alignments and phylogenetic analysis indicated that 499EST is a new member of the bacterial esterase/lipase family IV. The esterase reveals its optimum catalytic activity at 55 °C and pH 9.0. Kinetic studies showed that 499EST preferentially hydrolyzed middle-length acyl chains (C6-C8), especially p-nitrophenyl (p-NP) caproate (C6). Its thermostability and activity were strongly enhanced by adding 6 mM FeCl3. High stability in the presence of water-miscible solvents such as dimethyl sulfoxide and glycerol was observed. This enzyme also exhibits stability under harsh environmental conditions and enantioselectivity towards naproxen and ibuprofen esters, yielding the medically relevant (S)-enantiomers. In conclusion, according to our knowledge, 499EST is the first thermoalkalostable esterase derived from a Gram-negative thermoacidophilic bacterium.

Biochemical characterization of a first fungal esterase from Rhizomucor miehei showing high efficiency of ester synthesis

BACKGROUND

Esterases with excellent merits suitable for commercial use in ester production field are still insufficient. The aim of this research is to advance our understanding by seeking for more unusual esterases and revealing their characterizations for ester synthesis.

METHODOLOGY/PRINCIPAL FINDINGS

A novel esterase-encoding gene from Rhizomucor miehei (RmEstA) was cloned and expressed in Escherichia coli. Sequence analysis revealed a 975-bp ORF encoding a 324-amino-acid polypeptide belonging to the hormone-sensitive lipase (HSL) family IV and showing highest similarity (44%) to the Paenibacillus mucilaginosus esterase/lipase. Recombinant RmEstA was purified to homogeneity: it was 34 kDa by SDS-PAGE and showed optimal pH and temperature of 6.5 and 45°C, respectively. The enzyme was stable to 50°C, under a broad pH range (5.0-10.6). RmEstA exhibited broad substrate specificity toward p-nitrophenol esters and short-acyl-chain triglycerols, with highest activities (1,480 U mg(-1) and 228 U mg(-1)) for p-nitrophenyl hexanoate and tributyrin, respectively. RmEstA efficiently synthesized butyl butyrate (92% conversion yield) when immobilized on AOT-based organogel.

CONCLUSION

RmEstA has great potential for industrial applications. RmEstA is the first reported esterase from Rhizomucor miehei.

Cloning, expression, and characterization of a recombinant esterase from cold-adapted Pseudomonas mandelii

A gene coding for the extracellular esterase (EstK) was cloned from the psychrotrophic bacterium Pseudomonas mandelii based on its partial amino acid sequence as determined by mass spectrometry. The entire open reading frame consisting of 1,011 bp was expressed in Escherichia coli as a soluble protein and purified by nickel-chelated affinity chromatography and Capto Q column chromatography. Here, we show that the 33-kDa recombinant EstK protein (rEstKsp) had a substrate preference for esters of short-chain fatty acids, especially, p-nitrophenyl acetate. Optimum activity of rEstKsp was at pH 8.5 and 40 °C. The esterase activity remained similar from a range of 4∼20 °C, but the maximum activity varied depending upon pH. With p-nitrophenyl acetate as the substrate, K (M) was 210 μM and k (cat) was 3.4 s(-1). Circular dichroism and fluorescence spectroscopy results revealed that rEstKsp had a predominantly α-helical structure and maintained its folded state at 4∼40 °C. Interestingly, the tertiary structure of rEstKsp was predicted based on the structures of other hyperthermophilic esterases. Our results demonstrated that both native and rEstKsp are active at low temperatures and have a unique substrate preference for p-nitrophenyl acetate.

QsdH, a novel AHL lactonase in the RND-type inner membrane of marine Pseudoalteromonas byunsanensis strain 1A01261

N-acyl-homoserine lactones (AHLs) are the main quorum-sensing (QS) signals in gram-negative bacteria. AHLs trigger the expression of genes for particular biological functions when their density reaches a threshold. In this study, we identified and cloned the qsdH gene by screening a genomic library of Pseudoalteromonas byunsanensis strain 1A01261, which has AHL-degrading activity. The qsdH gene encoded a GDSL hydrolase found to be located in the N-terminus of a multidrug efflux transporter protein of the resistance-nodulation-cell division (RND) family. We further confirmed that the GDSL hydrolase, QsdH, exhibited similar AHL-degrading activity to the full-length ORF protein. QsdH was expressed and purified to process the N-terminal signal peptide yielding a 27-kDa mature protein. QsdH was capable of inactivating AHLs with an acyl chain ranging from C₄ to C₁₄ with or without 3-oxo substitution. High-performance liquid chromatography (HPLC) and electrospray ionization-mass spectrometry (ESI-MS) analyses showed that QsdH functioned as an AHL lactonase to hydrolyze the ester bond of the homoserine lactone ring of AHLs. In addition, site-directed mutagenesis demonstrated that QsdH contained oxyanion holes (Ser-Gly-Asn) in conserved blocks (I, II, and III), which had important roles in its AHL-degrading activity. Furthermore, the lactonase activity of QsdH was slightly promoted by several divalent ions. Using in silico prediction, we concluded that QsdH was located at the first periplasmic loop of the multidrug efflux transporter protein, which is essential to substrate selectivity for these efflux pumps. These findings led us to assume that the QsdH lactonase and C-terminal efflux pump might be effective in quenching QS of the P. byunsanensis strain 1A01261. Moreover, it was observed that recombinant Escherichia coli producing QsdH proteins attenuated the plant pathogenicity of Erwinia carotovora, which might have potential to control of gram-negative pathogenic bacteria.

Purification and biochemical characterization of a cold-active lipase from Antarctic sea ice bacteria Pseudoalteromonas sp. NJ 70

An extracellular cold-active lipase from Antarctic sea ice bacteria Pseudoalteromonas sp. NJ 70 was purified and characterized. The overall purification based on lipase activity was 27.5-fold with a yield of 25.4 %. The purified lipase showed as a single band on SDS-PAGE with an apparent molecular weight of 37 kDa. The optimum temperature and pH were 35 °C and 7.0, respectively. The lipase activity was enhanced by Ca(2+) and Mg(2+), while was partially inhibited by other metals such as Cu(2+), Zn(2+), Ba(2+), Pb(2+), Fe(2+) and Mn(2+). The lipase had high tolerance to a wide range of NaCl concentrations (0-2 M NaCl). It exhibited high levels of activity in the presence of DTT, Thiourea, H(2)O(2) as well as in the presence of various detergents such as Span 60, Tween-80, Triton X-100. In addition, the lipase showed a preference for long-chain p-nitrophenyl esters (C(12)-C(18)). These results indicated that this lipase could be a novel cold-active lipase.

A cold-adapted esterase of a novel marine isolate, Pseudoalteromonas arctica: gene cloning, enzyme purification and characterization

A gene encoding an esterase (estO) was identified and sequenced from a gene library screen of the psychrotolerant bacterium Pseudoalteromonas arctica. Analysis of the 1,203 bp coding region revealed that the deduced peptide sequence is composed of 400 amino acids with a predicted molecular mass of 44.1 kDa. EstO contains a N-terminal esterase domain and an additional OsmC domain at the C-terminus (osmotically induced family of proteins). The highly conserved five-residue motif typical for all alpha/beta hydrolases (G x S x G) was detected from position 104 to 108 together with a putative catalytic triad consisting of Ser(106), Asp(196), and His(225). Sequence comparison showed that EstO exhibits 90% amino acid identity with hypothetical proteins containing similar esterase and OsmC domains but only around 10% identity to the amino acid sequences of known esterases. EstO variants with and without the OsmC domain were produced and purified as His-tag fusion proteins in E. coli. EstO displayed an optimum pH of 7.5 and optimum temperature of 25 degrees C with more than 50% retained activity at the freezing point of water. The thermostability of EstO (50% activity after 5 h at 40 degrees C) dramatically increased in the truncated variant (50% activity after 2.5 h at 90 degrees C). Furthermore, the esterase displays broad substrate specificity for esters of short-chain fatty acids (C(2)-C(8)).

Structure of EstA esterase from psychrotrophic Pseudoalteromonas sp. 643A covalently inhibited by monoethylphosphonate

The crystal structure of the esterase EstA from the cold-adapted bacterium Pseudoalteromonas sp. 643A was determined in a covalently inhibited form at a resolution of 1.35 A. The enzyme has a typical SGNH hydrolase structure consisting of a single domain containing a five-stranded beta-sheet, with three helices at the convex side and two helices at the concave side of the sheet, and is ornamented with a couple of very short helices at the domain edges. The active site is located in a groove and contains the classic catalytic triad of Ser, His and Asp. In the structure of the crystal soaked in diethyl p-nitrophenyl phosphate (DNP), the catalytic serine is covalently connected to a phosphonate moiety that clearly has only one ethyl group. This is the only example in the Protein Data Bank of a DNP-inhibited enzyme with covalently bound monoethylphosphate.

Extracellular secretion of Pseudoalteromonas sp. cold-adapted esterase in Escherichia coli in the presence of Pseudoalteromonas sp. components of ABC transport system

Recently we described identification and characterization of GDSL esterase EstA from psychrotrophic bacterium Pseudoalteromonas sp. 643A. Attempts to obtain heterologous overexpression of this enzyme in Escherichia coli system were not satisfactory. The EstA protein was expressed as inclusion bodies, most of that were inactive after purification step, and the recovery of esterolytic activity was very low after refolding. Based on the sequence analysis we found that the esterase EstA gene is clustered with three genes encoding components of ABC transport system. These genes, designated abc1, abc2, and abc3 encode an ATP-binding protein (ABC1) and two permease proteins (ABC2 and ABC3). In present study, to obtain larger amounts of the active cold-adapted EstA esterase from Pseudoalteromonas sp. 643A, we designed a two-plasmid E. coli expression system where the gene encoding EstA enzyme was cloned into pET30b(+) expression vector and three genes encoding components of ABC transport system were cloned into pACYC-pBAD vector. It was shown that the created expression system was useful for extracellular production of active EstA enzyme which was purified from the culture medium. In the presence of all the three transporter proteins the secretion of EstA was at the highest level. When one or two of these components were missing, EstA secretion was also possible, but not so effective. It indicates that ABC2 and ABC3 proteins of Pseudoalteromonas sp. 643A could be replaced with their homologous proteins of E. coli.