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da Silva AS, Adriani PP, de Oliveira GS, Rocha ARL, Perpétuo EA, Dias MVB, Chambergo FS. Biochemical characterization of an esterase from Thermobifida fusca YX with acetyl xylan esterase activity. Mol Biol Rep 2024; 51:767. [PMID: 38878205 DOI: 10.1007/s11033-024-09601-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2024] [Accepted: 05/01/2024] [Indexed: 06/29/2024]
Abstract
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.
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Affiliation(s)
- Adriana S da Silva
- Escola de Artes, Ciências e HumanidadesErmelino Matarazzo, Universidade de São Paulo, 1000 Av. Arlindo Bettio, São Paulo, CEP: 3828-000, Brazil
| | - Patricia P Adriani
- Departamento de Farmacologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brazil
| | - Gabriel S de Oliveira
- Departamento de Microbiologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brazil
| | | | - Elen A Perpétuo
- Bio4Tec, Centro de Capacitação e Pesquisa em Meio Ambiente, CEPEMA-POLI-USP, Universidade de São Paulo, Cubatão, Brazil
- Institute of Marine Sciences (IMar), Federal University of Sao Paulo, Santos, Brazil
| | - Marcio V B Dias
- Departamento de Microbiologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brazil
| | - Felipe S Chambergo
- Escola de Artes, Ciências e HumanidadesErmelino Matarazzo, Universidade de São Paulo, 1000 Av. Arlindo Bettio, São Paulo, CEP: 3828-000, Brazil.
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2
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Wang X, Nong S, Li J, Liu Y, Wu Q, Huang Z, Xu B, Ding J. Biochemical characterization of an acetylesterase from Bacillus subtilis and its application for 7-aminocephalosporanic acid deacetylation. Front Microbiol 2023; 14:1164815. [PMID: 37206334 PMCID: PMC10189120 DOI: 10.3389/fmicb.2023.1164815] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2023] [Accepted: 03/30/2023] [Indexed: 05/21/2023] Open
Abstract
Deacetyl-7-aminocephalosporanic acid (D-7-ACA), which could be converted from 7-aminocephalosporanic acid (7-ACA), is a crucial starting material that is used for synthesizing industrial semisynthetic β-lactam antibiotics. Enzymes involved in the conversion from 7-ACA to D-7-ACA present critical resources in the pharmaceutical industry. In the present study, a putative acetylesterase, EstSJ, identified from Bacillus subtilis KATMIRA1933, was first heterologously expressed in Escherichia coli BL21(DE3) cells and biochemically characterized. EstSJ belongs to carbohydrate esterase family 12 and is active on short-chain acyl esters from p-NPC2 to p-NPC6. Multiple sequence alignments showed that EstSJ was also an SGNH family esterase with a typical GDS(X) motif at its N-terminal end and a catalytic triad composed of Ser186-Asp354-His357. The purified EstSJ displayed the highest specific activity of 1,783.52 U mg-1 at 30°C and pH 8.0, and was stable within the pH range of 5.0-11.0. EstSJ can deacetylate the C3' acetyl group of 7-ACA to generate D-7-ACA, and the deacetylation activity was 4.50 U mg-1. Based on the structural and molecular docking with 7-ACA, the catalytic active sites (Ser186-Asp354-His357) together with four substrate-binding residues (Asn259, Arg295, Thr355, and Leu356) of EstSJ are revealed. This study provided a promising 7-ACA deacetylase candidate that could be applied to produce D-7-ACA from 7-ACA in the pharmaceutical industry.
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Nguyen DL, Hwang J, Kim EJ, Lee JH, Han SJ. Production and Characterization of a Recombinant Cold-Active Acetyl Xylan Esterase from Psychrophilic Paenibacillus sp. R4 Strain. APPL BIOCHEM MICRO+ 2022. [DOI: 10.1134/s0003683822040123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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4
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Bhattacharyya M, Basu S, Dhar R, Dutta TK. Phthalate hydrolase: distribution, diversity and molecular evolution. ENVIRONMENTAL MICROBIOLOGY REPORTS 2022; 14:333-346. [PMID: 34816599 DOI: 10.1111/1758-2229.13028] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2021] [Revised: 11/08/2021] [Accepted: 11/09/2021] [Indexed: 05/12/2023]
Abstract
The alpha/beta-fold superfamily of hydrolases is rapidly becoming one of the largest groups of structurally related enzymes with diverse catalytic functions. In this superfamily of enzymes, esterase deserves special attention because of their wide distribution in biological systems and importance towards environmental and industrial applications. Among various esterases, phthalate hydrolases are the key alpha/beta enzymes involved in the metabolism of structurally diverse estrogenic phthalic acid esters, ubiquitously distributed synthetic chemicals, used as plasticizer in plastic manufacturing processes. Although they vary both at the sequence and functional levels, these hydrolases use a similar acid-base-nucleophile catalytic mechanism to catalyse reactions on structurally different substrates. The current review attempts to present insights on phthalate hydrolases, describing their sources, structural diversities, phylogenetic affiliations and catalytically different types or classes of enzymes, categorized as diesterase, monoesterase and diesterase-monoesterase, capable of hydrolysing phthalate diester, phthalate monoester and both respectively. Furthermore, available information on in silico analyses and site-directed mutagenesis studies revealing structure-function integrity and altered enzyme kinetics have been highlighted along with the possible scenario of their evolution at the molecular level.
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Affiliation(s)
| | - Suman Basu
- Department of Microbiology, Bose Institute, Kolkata, West Bengal, India
| | - Rinita Dhar
- Department of Microbiology, Bose Institute, Kolkata, West Bengal, India
| | - Tapan K Dutta
- Department of Microbiology, Bose Institute, Kolkata, West Bengal, India
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5
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Xu J, Zhao X, Yao Q, Zong W, Dai S, Deng Z, Liu S, Yun J, Yang X, Li H. Cloning, characterization of a novel acetyl xylan esterase, and its potential application on wheat straw utilization. ALL LIFE 2021. [DOI: 10.1080/26895293.2021.1947393] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Affiliation(s)
- Jin Xu
- School of Life Sciences and Biopharmaceuticals, Guangdong Pharmaceutical University, Guangzhou, People’s Republic of China
- Guangdong Key Laboratory of Bioactive Drug Research, Guangzhou, People’s Republic of China
| | - Xiaoshen Zhao
- School of Life Sciences and Biopharmaceuticals, Guangdong Pharmaceutical University, Guangzhou, People’s Republic of China
- Guangdong Key Laboratory of Bioactive Drug Research, Guangzhou, People’s Republic of China
| | - Qian Yao
- School of Life Sciences and Biopharmaceuticals, Guangdong Pharmaceutical University, Guangzhou, People’s Republic of China
- Guangdong Key Laboratory of Bioactive Drug Research, Guangzhou, People’s Republic of China
| | - Wei Zong
- School of Life Sciences and Biopharmaceuticals, Guangdong Pharmaceutical University, Guangzhou, People’s Republic of China
- Guangdong Key Laboratory of Bioactive Drug Research, Guangzhou, People’s Republic of China
| | - Shuang Dai
- School of Life Sciences and Biopharmaceuticals, Guangdong Pharmaceutical University, Guangzhou, People’s Republic of China
- Guangdong Key Laboratory of Bioactive Drug Research, Guangzhou, People’s Republic of China
| | - Zujun Deng
- School of Life Sciences and Biopharmaceuticals, Guangdong Pharmaceutical University, Guangzhou, People’s Republic of China
- Guangdong Key Laboratory of Bioactive Drug Research, Guangzhou, People’s Republic of China
| | - Shan Liu
- Guangzhou Basic Clean Cosmetics Manufacturing Co., Ltd, Guangzhou, People’s Republic of China
| | - Jeonyun Yun
- Guangzhou Basic Clean Cosmetics Manufacturing Co., Ltd, Guangzhou, People’s Republic of China
| | - Xiong Yang
- Guangzhou Basic Clean Cosmetics Manufacturing Co., Ltd, Guangzhou, People’s Republic of China
| | - He Li
- School of Life Sciences and Biopharmaceuticals, Guangdong Pharmaceutical University, Guangzhou, People’s Republic of China
- Guangdong Key Laboratory of Bioactive Drug Research, Guangzhou, People’s Republic of China
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6
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Karnaouri A, Zerva A, Christakopoulos P, Topakas E. Screening of Recombinant Lignocellulolytic Enzymes Through Rapid Plate Assays. Methods Mol Biol 2021; 2178:479-503. [PMID: 33128767 DOI: 10.1007/978-1-0716-0775-6_30] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
In the search for novel biomass-degrading enzymes through mining microbial genomes, it is necessary to apply functional tests during high-throughput screenings, which are capable of detecting enzymatic activities directly by way of plate assay. Using the most efficient expression systems of Escherichia coli and Pichia pastoris, the production of a high amount of His-tagged recombinant proteins could be thrived, allowing the one-step isolation by affinity chromatography. Here, we describe simple and efficient assay techniques for the detection of various biomass-degrading enzymatic activities on agar plates, such as cellulolytic, hemicellulolytic, and ligninolytic activities and their isolation using immobilized-metal affinity chromatography.
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Affiliation(s)
- Anthi Karnaouri
- Industrial Biotechnology and Biocatalysis Group, Biotechnology Laboratory, Department of Synthesis and Development of Industrial Processes, School of Chemical Engineering, National Technical University of Athens, Athens, Greece
| | - Anastasia Zerva
- Industrial Biotechnology and Biocatalysis Group, Biotechnology Laboratory, Department of Synthesis and Development of Industrial Processes, School of Chemical Engineering, National Technical University of Athens, Athens, Greece
| | - Paul Christakopoulos
- Biochemical Process Engineering, Chemical Engineering, Department of Civil, Environmental and Natural Resources Engineering, Luleå University of Technology, Luleå, Sweden
| | - Evangelos Topakas
- Industrial Biotechnology and Biocatalysis Group, Biotechnology Laboratory, Department of Synthesis and Development of Industrial Processes, School of Chemical Engineering, National Technical University of Athens, Athens, Greece.
- Biochemical Process Engineering, Chemical Engineering, Department of Civil, Environmental and Natural Resources Engineering, Luleå University of Technology, Luleå, Sweden.
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Chettri D, Verma AK, Verma AK. Innovations in CAZyme gene diversity and its modification for biorefinery applications. BIOTECHNOLOGY REPORTS (AMSTERDAM, NETHERLANDS) 2020; 28:e00525. [PMID: 32963975 PMCID: PMC7490808 DOI: 10.1016/j.btre.2020.e00525] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Revised: 08/04/2020] [Accepted: 08/30/2020] [Indexed: 02/07/2023]
Abstract
For sustainable growth, concept of biorefineries as recourse to the "fossil derived" energy source is important. Here, the Carbohydrate Active enZymes (CAZymes) play decisive role in generation of biofuels and related sugar-based products utilizing lignocellulose as a carbon source. Given their industrial significance, extensive studies on the evolution of CAZymes have been carried out. Various bacterial and fungal organisms have been scrutinized for the development of CAZymes, where advance techniques for strain enhancement such as CRISPR and analysis of specific expression systems have been deployed. Specific Omic-based techniques along with protein engineering have been adopted to unearth novel CAZymes and improve applicability of existing enzymes. In-Silico computational research and functional annotation of new CAZymes to synergy experiments are being carried out to devise cocktails of enzymes for use in biorefineries. Thus, with the establishment of these technologies, increased diversity of CAZymes with broad span of functions and applications is seen.
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Verma D, Satyanarayana T. Xylanolytic Extremozymes Retrieved From Environmental Metagenomes: Characteristics, Genetic Engineering, and Applications. Front Microbiol 2020; 11:551109. [PMID: 33042057 PMCID: PMC7527525 DOI: 10.3389/fmicb.2020.551109] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2020] [Accepted: 08/21/2020] [Indexed: 01/29/2023] Open
Abstract
Xylanolytic enzymes have extensive applications in paper, food, and feed, pharmaceutical, and biofuel industries. These industries demand xylanases that are functional under extreme conditions, such as high temperature, acidic/alkaline pH, and others, which are prevailing in bioprocessing industries. Despite the availability of several xylan-hydrolyzing enzymes from cultured microbes, there is a huge gap between what is available and what industries require. DNA manipulations as well as protein-engineering techniques are also not quite satisfactory in generating xylan-hydrolyzing extremozymes. With a compound annual growth rate of 6.6% of xylan-hydrolyzing enzymes in the global market, there is a need for xylanolytic extremozymes. Therefore, metagenomic approaches have been employed to uncover hidden xylanolytic genes that were earlier inaccessible in culture-dependent approaches. Appreciable success has been achieved in retrieving several unusual xylanolytic enzymes with novel and desirable characteristics from different extreme environments using functional and sequence-based metagenomic approaches. Moreover, the Carbohydrate Active Enzymes database includes approximately 400 GH-10 and GH-11 unclassified xylanases. This review discusses sources, characteristics, and applications of xylanolytic enzymes obtained through metagenomic approaches and their amelioration by genetic engineering techniques.
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Affiliation(s)
- Digvijay Verma
- Department of Microbiology, Babasaheb Bhimrao Ambedkar (Central) University, Lucknow, India
| | - Tulasi Satyanarayana
- Department of Biological Sciences and Engineering, Netaji Subhas University of Technology, Dwarka, New Delhi, India
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Zhu D, Adebisi WA, Ahmad F, Sethupathy S, Danso B, Sun J. Recent Development of Extremophilic Bacteria and Their Application in Biorefinery. Front Bioeng Biotechnol 2020; 8:483. [PMID: 32596215 PMCID: PMC7303364 DOI: 10.3389/fbioe.2020.00483] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Accepted: 04/27/2020] [Indexed: 12/22/2022] Open
Abstract
The biorefining technology for biofuels and chemicals from lignocellulosic biomass has made great progress in the world. However, mobilization of laboratory research toward industrial setup needs to meet a series of criteria, including the selection of appropriate pretreatment technology, breakthrough in enzyme screening, pathway optimization, and production technology, etc. Extremophiles play an important role in biorefinery by providing novel metabolic pathways and catalytically stable/robust enzymes that are able to act as biocatalysts under harsh industrial conditions on their own. This review summarizes the potential application of thermophilic, psychrophilic alkaliphilic, acidophilic, and halophilic bacteria and extremozymes in the pretreatment, saccharification, fermentation, and lignin valorization process. Besides, the latest studies on the engineering bacteria of extremophiles using metabolic engineering and synthetic biology technologies for high-efficiency biofuel production are also introduced. Furthermore, this review explores the comprehensive application potential of extremophiles and extremozymes in biorefinery, which is partly due to their specificity and efficiency, and points out the necessity of accelerating the commercialization of extremozymes.
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Affiliation(s)
- Daochen Zhu
- Biofuels Institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, China
- State Key Laboratory of Applied Microbiology Southern China, Guangdong Provincial Key Laboratory of Microbial Culture Collection and Application, Guangdong Open Laboratory of Applied Microbiology, Guangdong Institute of Microbiology, Guangzhou, China
| | - Wasiu Adewale Adebisi
- Biofuels Institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, China
| | - Fiaz Ahmad
- Biofuels Institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, China
| | - Sivasamy Sethupathy
- Biofuels Institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, China
| | - Blessing Danso
- Biofuels Institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, China
| | - Jianzhong Sun
- Biofuels Institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, China
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Ding J, Zhou Y, Zhu H, Deng M, Gao Y, Yang Y, Huang Z. Characterization of EstZY: A new acetylesterase with 7-aminocephalosporanic acid deacetylase activity from Alicyclobacillus tengchongensis. Int J Biol Macromol 2020; 148:333-341. [DOI: 10.1016/j.ijbiomac.2020.01.151] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2019] [Revised: 12/04/2019] [Accepted: 01/15/2020] [Indexed: 02/03/2023]
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11
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Malgas S, Mafa MS, Mkabayi L, Pletschke BI. A mini review of xylanolytic enzymes with regards to their synergistic interactions during hetero-xylan degradation. World J Microbiol Biotechnol 2019; 35:187. [PMID: 31728656 DOI: 10.1007/s11274-019-2765-z] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Accepted: 11/06/2019] [Indexed: 10/25/2022]
Abstract
This review examines the recent models describing the mode of action of various xylanolytic enzymes and how these enzymes can be applied (sequentially or simultaneously) with their distinctive roles in mind to achieve efficient xylan degradation. With respect to homeosynergy, synergism appears to be as a result of β-xylanase and/or oligosaccharide reducing-end β-xylanase liberating xylo-oligomers (XOS) that are preferred substrates of the processive β-xylosidase. With regards to hetero-synergism, two cross relationships appear to exist and seem to be the reason for synergism between the enzymes during xylan degradation. These cross relations are the debranching enzymes such as α-glucuronidase or side-chain cleaving enzymes such as carbohydrate esterases (CE) removing decorations that would have hindered back-bone-cleaving enzymes, while backbone-cleaving-enzymes liberate XOS that are preferred substrates of the debranching and side-chain-cleaving enzymes. This interaction is demonstrated by high yields in co-production of xylan substituents such as arabinose, glucuronic acid and ferulic acid, and XOS. Finally, lytic polysaccharide monooxygenases (LPMO) have also been implicated in boosting whole lignocellulosic biomass or insoluble xylan degradation by glycoside hydrolases (GH) by possibly disrupting entangled xylan residues. Since it has been observed that the same enzyme (same Enzyme Commission, EC, classification) from different GH or CE and/or AA families can display different synergistic interactions with other enzymes due to different substrate specificities and properties, in this review, we propose an approach of enzyme selection (and mode of application thereof) during xylan degradation, as this can improve the economic viability of the degradation of xylan for producing precursors of value added products.
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Affiliation(s)
- Samkelo Malgas
- Enzyme Science Programme (ESP), Department of Biochemistry and Microbiology, Rhodes University, Grahamstown, Eastern Cape, 6140, South Africa
| | - Mpho S Mafa
- Enzyme Science Programme (ESP), Department of Biochemistry and Microbiology, Rhodes University, Grahamstown, Eastern Cape, 6140, South Africa.,Protein Structure-Function Research Unit (PSFRU), School of Molecular and Cell Biology, Wits University, Johannesburg, Gauteng, 2000, South Africa
| | - Lithalethu Mkabayi
- Enzyme Science Programme (ESP), Department of Biochemistry and Microbiology, Rhodes University, Grahamstown, Eastern Cape, 6140, South Africa
| | - Brett I Pletschke
- Enzyme Science Programme (ESP), Department of Biochemistry and Microbiology, Rhodes University, Grahamstown, Eastern Cape, 6140, South Africa.
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Crystal structure and functional characterization of a cold-active acetyl xylan esterase (PbAcE) from psychrophilic soil microbe Paenibacillus sp. PLoS One 2018; 13:e0206260. [PMID: 30379876 PMCID: PMC6209228 DOI: 10.1371/journal.pone.0206260] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Accepted: 10/09/2018] [Indexed: 12/27/2022] Open
Abstract
Cold-active acetyl xylan esterases allow for reduced bioreactor heating costs in bioenergy production. Here, we isolated and characterized a cold-active acetyl xylan esterase (PbAcE) from the psychrophilic soil microbe Paenibacillus sp. R4. The enzyme hydrolyzes glucose penta-acetate and xylan acetate, reversibly producing acetyl xylan from xylan, and it shows higher activity at 4°C than at 25°C. We solved the crystal structure of PbAcE at 2.1-Å resolution to investigate its active site and the reason for its low-temperature activity. Structural analysis showed that PbAcE forms a hexamer with a central substrate binding tunnel, and the inter-subunit interactions are relatively weak compared with those of its mesophilic and thermophilic homologs. PbAcE also has a shorter loop and different residue composition in the β4–α3 and β5–α4 regions near the substrate binding site. Flexible subunit movements and different active site loop conformations may enable the strong low-temperature activity and broad substrate specificity of PbAcE. In addition, PbAcE was found to have strong activity against antibiotic compound substrates, such as cefotaxime and 7-amino cephalosporanic acid (7-ACA). In conclusion, the PbAcE structure and our biochemical results provide the first example of a cold-active acetyl xylan esterase and a starting template for structure-based protein engineering.
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