A novel, versatile family IV carboxylesterase exhibits high stability and activity in a broad pH spectrum

Temperature-dependent alcohol acyltransferase reactions as the main enzymatic way to produce short-chain (C4-C8) and medium-chain (C9-C13) esters over the whole Daqu-making process

BACKGROUND

The ester-synthesis enzymes influenced by environmental factors during Daqu-making process largely determine the flavor of Chinese liquor, but the main ester-synthesis enzyme and its key influencer remain unclear. Here, the volatile ester profiles over the whole Daqu-making process, under different treatments, for at least 90 days, were carefully analyzed, and the potential ester-synthesis enzymes, as well as their dependently environmental factors, were explored.

RESULTS

In the detected 46 volatile esters, only the short-chain (C4-C8) and medium-chain (C9-C13) ester content obviously changed, as the primary contributor discriminating different samples. Their trends were both consistent with that of the alcohols and the primary metabolism, which included alcohol acyltransferases (AATs) reaction with alcohols and acyl-CoAs as the substrates. Among the potential ester-synthesis enzymes, the typical AAT activity also exhibited the highest correlation with the short- and medium-chain esters (r > 0.78, P < 0.05). The Mantel test between environmental factors and ester production showed that temperature of Daqu was directly correlated with the short-chain esters (r = 0.58, P < 0.01) and AAT activity (r = 0.56, P < 0.01). Further, the short- and medium-chain ester content in Daqu under the treatment nearer to the reported optimal temperature of 40-50 °C of AATs reaction was overall higher than that of the other treatment Daqu.

CONCLUSION

This study revealed that the temperature-dependent AATs reaction was the main enzymatic method producing the short- and medium-chain esters over the whole Daqu-making process. The results could contribute to the flavor improvement of Baijiu. © 2022 Society of Chemical Industry.

An overview of mammalian and microbial hormone-sensitive lipases (lipolytic family IV): biochemical properties and industrial applications

In mammals, hormone-sensitive lipase (EC 3.1.1.79) is an intracellular lipase that significantly regulates lipid metabolism. Mammalian HSL is more active towards diacylglycerol but lacks a lid covering the active site. Dyslipidemia, hepatic steatosis, cancer, and cancer-associated cachexia are symptoms of HSL pathophysiology. Certain microbial proteins show a sequence homologous to the catalytic domain of mammalian HSL, hence called microbial HSL. They possess a funnel-shaped substrate-binding pocket and restricted length of acyl chain esters, thus known as esterases. These enzymes have broad substrate specificities and are capable of stereo, regio, and enantioselective, making them attractive biocatalysts in a wide range of industrial applications in the production of flavors, pharmaceuticals, biosensors, and fine chemicals. This review will provide insight into mammalian and microbial HSLs, their sources, structural features related to substrate specificity, thermal stability, and their applications.

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.

Metagenomic Screening for Lipolytic Genes Reveals an Ecology-Clustered Distribution Pattern

Lipolytic enzymes are one of the most important enzyme types for application in various industrial processes. Despite the continuously increasing demand, only a small portion of the so far encountered lipolytic enzymes exhibit adequate stability and activities for biotechnological applications. To explore novel and/or extremophilic lipolytic enzymes, microbial consortia in two composts at thermophilic stage were analyzed using function-driven and sequence-based metagenomic approaches. Analysis of community composition by amplicon-based 16S rRNA genes and transcripts, and direct metagenome sequencing revealed that the communities of the compost samples were dominated by members of the phyla Actinobacteria, Proteobacteria, Firmicutes, Bacteroidetes, and Chloroflexi. Function-driven screening of the metagenomic libraries constructed from the two samples yielded 115 unique lipolytic enzymes. The family assignment of these enzymes was conducted by analyzing the phylogenetic relationship and generation of a protein sequence similarity network according to an integrated classification system. The sequence-based screening was performed by using a newly developed database, containing a set of profile Hidden Markov models, highly sensitive and specific for detection of lipolytic enzymes. By comparing the lipolytic enzymes identified through both approaches, we demonstrated that the activity-directed complements sequence-based detection, and vice versa. The sequence-based comparative analysis of lipolytic genes regarding diversity, function and taxonomic origin derived from 175 metagenomes indicated significant differences between habitats. Analysis of the prevalent and distinct microbial groups providing the lipolytic genes revealed characteristic patterns and groups driven by ecological factors. The here presented data suggests that the diversity and distribution of lipolytic genes in metagenomes of various habitats are largely constrained by ecological factors.

Metagenomic Approaches as a Tool to Unravel Promising Biocatalysts from Natural Resources: Soil and Water

Natural resources are considered a promising source of microorganisms responsible for producing biocatalysts with great relevance in several industrial areas. However, a significant fraction of the environmental microorganisms remains unknown or unexploited due to the limitations associated with their cultivation in the laboratory through classical techniques. Metagenomics has emerged as an innovative and strategic approach to explore these unculturable microorganisms through the analysis of DNA extracted from environmental samples. In this review, a detailed discussion is presented on the application of metagenomics to unravel the biotechnological potential of natural resources for the discovery of promising biocatalysts. An extensive bibliographic survey was carried out between 2010 and 2021, covering diverse metagenomic studies using soil and/or water samples from different types and locations. The review comprises, for the first time, an overview of the worldwide metagenomic studies performed in soil and water and provides a complete and global vision of the enzyme diversity associated with each specific environment.

Molecular Identification of Keratinase DgokerA from Deinococcus gobiensis for Feather Degradation

Keratin is a tough fibrous structural protein that is difficult to digest with pepsin and trypsin because of the presence of a large number of disulfide bonds. Keratin is widely found in agricultural waste. In recent years, especially, the development of the poultry industry has resulted in a large accumulation of feather keratin resources, which seriously pollute the environment. Keratinase can specifically attack disulfide bridges in keratin, converting them from complex to simplified forms. The keratinase thermal stability has drawn attention to various biotechnological industries. It is significant to identify keratinases and improve their thermostability from microorganism in extreme environments. In this study, the keratinases DgoKerA was identified in Deinococcus gobiensis I-0 from the Gobi desert. The amino acid sequence analysis revealed that DgoKerA was 58.68% identical to the keratinase MtaKerA from M. thermophila WR-220 and 40.94% identical to the classical BliKerA sequence from B. licheniformis PWD-1. In vitro enzyme activity analysis showed that DgoKerA exhibited an optimum temperature of 60 °C, an optimum pH of 7 and a specific enzyme activity of 51147 U/mg. DgoKerA can degrade intact feathers at 60 °C and has good potential for industrial applications. The molecular modification of DgoKerA was also carried out using site-directed mutagenesis, in which the mutant A350S enzyme activity was increased by nearly 30%, and the results provide a theoretical basis for the development and optimization of keratinase applications.

An integrated overview of bacterial carboxylesterase: Structure, function and biocatalytic applications

Carboxylesterases (CEs) are members of prominent esterase, and as their name imply, they catalyze the cleavage of ester linkages. By far, a considerable number of novel CEs have been identified to investigate their exquisite physiological and biochemical properties. They are abundant enzymes in nature, widely distributed in relatively broad temperature range and in various sources; both macroorganisms and microorganisms. Given the importance of these enzymes in broad industries, interest in the study of their mechanisms and structural-based engineering are greatly increasing. This review presents the current state of knowledge and understanding about the structure and functions of this ester-metabolizing enzyme, primarily from bacterial sources. In addition, the potential biotechnological applications of bacterial CEs are also encompassed. This review will be useful in understanding the molecular basis and structural protein of bacterial CEs that are significant for the advancement of enzymology field in industries.

Characterization of EstDR4, a Novel Cold-Adapted Insecticides-Metabolizing Esterase from Deinococcus radiodurans

Cold-adapted esterases are attracting increasing attention owing to their prospective use in biotechnology. In this study, a novel cold-adapted family Ⅳ esterase EstDR4 was identified and obtained from extremophile Deinococcus radiodurans (D. radiodurans). EstDR4 displayed significant substrate preference towards short and medium chain monoesters (C2–C12). It also showed regioselectivity, enantioselectivity and degradation effects on four insecticides. The optimum temperature and pH for EstDR4 activity were 30 °C and pH 8, respectively. Additionally, EstDR4 exhibited relatively high catalytic activity at 0 °C and high stability from 10–40 °C, with over 80% of its initial activity retained after 1 h of incubation. Moreover, EstDR4 activity was stimulated by Tween 80 and Triton X-100, and inhibited by metal ions such as Co2+, Cu2+ and Zn2+ and several organic solvents. Thus, this enzyme shows development potential for many industrial biotechnological applications, including the manufacture of thermolabile pharmaceutical products, cold-wash detergents and insecticide biodegradation.

A Novel Carboxylesterase Derived from a Compost Metagenome Exhibiting High Stability and Activity towards High Salinity

Halotolerant lipolytic enzymes have gained growing interest, due to potential applications under harsh conditions, such as hypersalinity and presence of organic solvents. In this study, a lipolytic gene, est56, encoding 287 amino acids was identified by functional screening of a compost metagenome. Subsequently, the gene was heterologously expressed, and the recombinant protein (Est56) was purified and characterized. Est56 is a mesophilic (T_opt 50 °C) and moderate alkaliphilic (pH_opt 8) enzyme, showing high thermostability at 30 and 40 °C. Strikingly, Est56 is halotolerant as it exhibited high activity and stability in the presence of up to 4 M NaCl or KCl. Est56 also displayed enhanced stability against high temperatures (50 and 60 °C) and urea (2, 4, and 6 M) in the presence of NaCl. In addition, the recently reported halotolerant lipolytic enzymes were summarized. Phylogenetic analysis grouped these enzymes into 13 lipolytic protein families. The majority (45%) including Est56 belonged to family IV. To explore the haloadaptation of halotolerant enzymes, the amino acid composition between halotolerant and halophilic enzymes was statistically compared. The most distinctive feature of halophilic from non-halophilic enzymes are the higher content of acidic residues (Asp and Glu), and a lower content of lysine, aliphatic hydrophobic (Leu, Met and Ile) and polar (Asn) residues. The amino acid composition and 3-D structure analysis suggested that the high content of acidic residues (Asp and Glu, 12.2%) and low content of lysine residues (0.7%), as well as the excess of surface-exposed acidic residues might be responsible for the haloadaptation of Est56.

Identification and characterization of a novel bacterial carbohydrate esterase from the bacterium Pantoea ananatis Sd-1 with potential for degradation of lignocellulose and pesticides

OBJECTIVE

Identification and characterization of a novel bacterial carbohydrate esterase (PaCes7) with application potential for lignocellulose and pesticide degradation.

RESULTS

PaCes7 was identified from the lignocellulolytic bacterium, Pantoea ananatis Sd-1 as a new carbohydrate esterase. Recombinant PaCes7 heterologously expressed in Escherichia coli showed a clear preference for esters with short-chain fatty acids and exhibited maximum activity towards α-naphthol acetate at 37 °C and pH 7.5. Purified PaCes7 exhibited its catalytic activity under mesophilic conditions and retained more than 40% activity below 30 °C. It displayed a relatively wide pH stability from pH 6-11. Furthermore, the enzyme was strongly resistant to Mg²⁺, Pb²⁺, and Co²⁺ and activated by K⁺ and Ca²⁺. Both P. ananatis Sd-1 and PaCes7 could degrade the pesticide carbaryl. Additionally, PaCes7 was shown to work in combination with cellulase and/or xylanase in rice straw degradation.

CONCLUSIONS

The data suggest that PaCes7 possesses promising biotechnological potential.

"Recombinant cold -adapted halotolerant, organic solvent-stable esterase (estHIJ) from Bacillus halodurans

Esterases and lipases enduring harsh conditions, including low temperature and extreme tolerance to organic solvents, have attracted great attention in recent times. In the current study, a full open reading frame of 747 bp that encodes a novel, cold-adapted esterase (estHIJ) of 248 amino acids from Bacillus halodurans strain NAH-Egypt was heterologously cloned and expressed in E. coli BL21 (DE3) Rosetta. Amino acid sequence analysis revealed that estHIJ belongs to family XIII of lipolytic enzymes, with a characteristic pentapeptide motif (G-L-S-L-G). The recombinant estHIJ was purified using Ni-affinity chromatography to homogeneity with purification fold, yield, specific activity, and molecular weight (MW) of 3.5, 47.5%, 19.8 U/mg and 29 kDa, respectively. The enzyme showed preferential substrate specificity towards pNP-acetate (C2), with catalytic efficiency of 46,825 min^-1 mM^-1 estHIJ displayed optimal activity at 30 °C and pH (7.0-8.0). estHIJ demonstrated robust stability in the presence of 50% (v/v) non-polar solvents and 4 M NaCl after 15 h and 6 h of incubation, respectively. The promising features of the recombinant estHIJ underpin its potential in several fields, e.g., the synthesis of pharmaceutical compounds and the food industry.

Biochemical profiles of two thermostable and organic solvent-tolerant esterases derived from a compost metagenome

Owing to the functional versatility and potential applications in industry, interest in lipolytic enzymes tolerant to organic solvents is increasing. In this study, functional screening of a compost soil metagenome resulted in identification of two lipolytic genes, est1 and est2, encoding 270 and 389 amino acids, respectively. The two genes were heterologously expressed and characterized. Est1 and Est2 are thermostable enzymes with optimal enzyme activities at 80 and 70 °C, respectively. A second-order rotatable design, which allows establishing the relationship between multiple variables with the obtained responses, was used to explore the combined effects of temperature and pH on esterase stability. The response curve indicated that Est1, and particularly Est2, retained high stability within a broad range of temperature and pH values. Furthermore, the effects of organic solvents on Est1 and Est2 activities and stabilities were assessed. Notably, Est2 activity was significantly enhanced (two- to tenfold) in the presence of ethanol, methanol, isopropanol, and 1-propanol over a concentration range between 6 and 30% (v/v). For the short-term stability (2 h of incubation), Est2 exhibited high tolerance against 60% (v/v) of ethanol, methanol, isopropanol, DMSO, and acetone, while Est1 activity resisted these solvents only at lower concentrations (below 30%, v/v). Est2 also displayed high stability towards some water-immiscible organic solvents, such as ethyl acetate, diethyl ether, and toluene. With respect to long-term stability, Est2 retained most of its activity after 26 days of incubation in the presence of 30% (v/v) ethanol, methanol, isopropanol, DMSO, or acetone. All of these features indicate that Est1 and Est2 possess application potential.

Structural and functional characterization of a novel lipolytic enzyme from a Brazilian Cerrado soil metagenomic library

OBJECTIVE

To isolate putative lipase enzymes by screening a Cerrado soil metagenomic library with novel features.

RESULTS

Of 6720 clones evaluated, Clone W (10,000 bp) presented lipolytic activity and four predicted coding sequences, one of them LipW. Characterization of a predicted esterase/lipase, LipW, showed 28% sequence identity with an arylesterase from Pseudomonas fluorescens (pdb|3HEA) from protein database (PDB). Phylogenetic analysis showed LipW clustered with family V lipases; however, LipW was clustered in different subclade belonged to family V, suggesting a different subgroup of family V. In addition, LipW presented a difference in family V GH motif, a glycine replaced by a serine in GH motif. Estimated molecular weight and stokes radius values of LipW were 29,338.67-29,411.98 Da and 2.58-2.83 nm, respectively. Optimal enzyme activity was observed at pH 9.0-9.5 and at 40 °C. Circular dichroism analysis estimated secondary structures percentages as approximately 45% α-helix and 15% β-sheet, consistent with the 3D structure predicted by homology.

CONCLUSION

Our results demonstrate the isolation of novel family V lipolytic enzyme with biotechnological applications from a metagenomic library.

Cloning, expression and characterization of cold active esterase (EstN7) from Bacillus cohnii strain N1: A novel member of family IV

Esterases and lipases from extremophiles have attracted great attention due to their unique characteristics and wide applications. In the present study, an open reading frame (ORF) encoding a novel cold active esterase (EstN7) from Bacillus cohnii strain N1 was cloned and expressed in Escherichia coli. The full-length esterase gene encoding a protein of 320 amino acids with estimated molecular weight of 37.0 kDa. Amino acid sequence analysis revealed that the EstN7 belongs to family IV lipases with a characteristic penta-peptide motif (GXSXG), the catalytic triad Ser, Asp, His and the conserved HGGG motif of the family IV. The recombinant enzyme was purified to apparent homogeneity using nickel-affinity chromatography with a purification fold of 5 and recovery 94.5%. The specific activity of the purified enzyme was 336.89 U/mg. The recombinant EstN7 showed optimal activity at 5 °C moreover, EstN7 displayed full robust stability in the presence of wide range of organic solvents. The purified enzyme had K_m and V_max of 45 ± 0.019 μM and 1113 μmol min^-1 mg^-1, respectively on p-NP-acetate. These promising characteristics of the recombinant EstN7 would underpin its possible usage with high potential in the synthesis of fragile compounds in pharmaceutical industries.

Characterization of a novel alkaline esterase from Altererythrobacter epoxidivorans CGMCC 1.7731T

A novel esterase gene (e25) was identified from Altererythrobacter epoxidivorans CGMCC 1.7731^T by genome sequence screening. The e25 gene is 948 nucleotides in length and encodes a 315 amino acid protein (E25) with a predicted molecular mass of 33,683 Da. A phylogenetic tree revealed that E25 belongs to the hormone-sensitive lipase (HSL) family of lipolytic enzymes. An activity assay of E25 showed that it exhibited the highest catalytic efficiency when using p-nitrophenyl caproate (C6) as a substrate. The optimum pH and temperature were determined to be approximately pH 9 and 45°C, and the K_m and V_max values were 0.12 mM and 1,772 µmol/min/mg, respectively. After an incubation at 40°C for 80 min, E25 retained 75% of its basal activity. The enzyme exhibited good tolerance to metal cations, such as Ba²⁺, Ca²⁺, and Cu²⁺ (10 mM), but its activity was strongly inhibited by Co²⁺, Ni²⁺, Mn²⁺, and Zn²⁺. The E25 enzyme was stimulated by glycerol and retained over 60% of its basal activity in the presence of 1% Tween-80 and Triton X-100. Overall, the activity of E25 under alkaline conditions and its organic solvent and detergent tolerance indicate that E25 could be useful as a novel industrial catalyst in biotechnological applications.