1
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Min K, Kim H, Park HJ, Lee S, Jung YJ, Yoon JH, Lee JS, Park K, Yoo YJ, Joo JC. Improving the catalytic performance of xylanase from Bacillus circulans through structure-based rational design. BIORESOURCE TECHNOLOGY 2021; 340:125737. [PMID: 34426235 DOI: 10.1016/j.biortech.2021.125737] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Revised: 08/03/2021] [Accepted: 08/05/2021] [Indexed: 06/13/2023]
Abstract
Endo-1,4-β-xylanase is one of the most important enzymes employed in biorefineries for obtaining fermentable sugars from hemicellulosic components. Herein, we aimed to improve the catalytic performance of Bacillus circulans xylanase (Bcx) using a structure-guided rational design. A systematic analysis of flexible motions revealed that the R49 component of Bcx (i) constrains the global conformational changes essential for substrate binding and (ii) is involved in modulating flexible motion. Site-saturated mutagenesis of the R49 residue led to the engineering of the active mutants with the trade-off between flexibility and rigidity. The most active mutant R49N improved the catalytic performance, including its catalytic efficiency (7.51-fold), conformational stability (0.7 °C improvement), and production of xylose oligomers (2.18-fold higher xylobiose and 1.72-fold higher xylotriose). The results discussed herein can be applied to enhance the catalytic performance of industrially important enzymes by controlling flexibility.
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Affiliation(s)
- Kyoungseon Min
- Gwangju Bio/Energy R&D Center, Korea Institute of Energy Research (KIER), Gwangju 61003, Republic of Korea
| | - Hoyong Kim
- Center for Bio-Based Chemistry, Korea Research Institute of Chemical Technology, Ulsan 44429, Republic of Korea
| | - Hyun June Park
- Department of Biotechnology, Duksung Women's University, Seoul 01369, Republic of Korea
| | - Siseon Lee
- Department of Biotechnology, The Catholic University of Korea, Bucheon-si, Gyeonggi-do 14662, Republic of Korea
| | - Ye Jean Jung
- Department of Biotechnology, The Catholic University of Korea, Bucheon-si, Gyeonggi-do 14662, Republic of Korea; Department of Biological and Chemical Engineering, Hongik University, Sejong Ro 2639, Jochiwon, Sejong City, Republic of Korea
| | - Ji Hyun Yoon
- Department of Biotechnology, The Catholic University of Korea, Bucheon-si, Gyeonggi-do 14662, Republic of Korea
| | - Jin-Suk Lee
- Gwangju Bio/Energy R&D Center, Korea Institute of Energy Research (KIER), Gwangju 61003, Republic of Korea
| | - Kyoungmoon Park
- Department of Biological and Chemical Engineering, Hongik University, Sejong Ro 2639, Jochiwon, Sejong City, Republic of Korea
| | - Young Je Yoo
- School of Chemical and Biological Engineering, Seoul National University, Seoul 08826, Republic of Korea
| | - Jeong Chan Joo
- Center for Bio-Based Chemistry, Korea Research Institute of Chemical Technology, Ulsan 44429, Republic of Korea; Department of Biotechnology, The Catholic University of Korea, Bucheon-si, Gyeonggi-do 14662, Republic of Korea.
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2
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Kalinina AN, Gordeeva TL, Sineoky SP. Expression of the Xylanase Gene from Paenibacillus brasilensis X1 in Pichia pastoris and Characteristics of the Recombinant Enzyme. APPL BIOCHEM MICRO+ 2019. [DOI: 10.1134/s0003683819080064] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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3
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Shah V, Pierre B, Kirtadze T, Shin S, Kim JR. Stabilization of Bacillus circulans xylanase by combinatorial insertional fusion to a thermophilic host protein. Protein Eng Des Sel 2017; 30:281-290. [PMID: 28100651 DOI: 10.1093/protein/gzw081] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Accepted: 12/21/2016] [Indexed: 11/15/2022] Open
Abstract
High thermostability of an enzyme is critical for its industrial application. While many engineering approaches such as mutagenesis have enhanced enzyme thermostability, they often suffer from reduced enzymatic activity. A thermally stabilized enzyme with unchanged amino acids is preferable for subsequent functional evolution necessary to address other important industrial needs. In the research presented here, we applied insertional fusion to a thermophilic maltodextrin-binding protein from Pyrococcus furiosus (PfMBP) in order to improve the thermal stability of Bacillus circulans xylanase (BCX). Specifically, we used an engineered transposon to construct a combinatorial library of randomly inserted BCX into PfMBP. The library was then subjected to functional screening to identify successful PfMBP-BCX insertion complexes, PfMBP-BCX161 and PfMBP-BCX165, displaying substantially improved kinetic stability at elevated temperatures compared to unfused BCX and other controls. Results from subsequent characterizations were consistent with the view that lowered aggregation of BCX and reduced conformational flexibility at the termini was responsible for increased thermal stability. Our stabilizing approach neither sacrificed xylanase activity nor required changes in the BCX amino acid sequence. Overall, the current study demonstrated the benefit of combinatorial insertional fusion to PfMBP as a systematic tool for the creation of enzymatically active and thermostable BCX variants.
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Affiliation(s)
- Vandan Shah
- Othmer-Jacobs Department of Chemical and Biomolecular Engineering, New York University, 6 MetroTech Center, Brooklyn, NY 11201, USA
| | - Brennal Pierre
- Othmer-Jacobs Department of Chemical and Biomolecular Engineering, New York University, 6 MetroTech Center, Brooklyn, NY 11201, USA
| | - Tamari Kirtadze
- Othmer-Jacobs Department of Chemical and Biomolecular Engineering, New York University, 6 MetroTech Center, Brooklyn, NY 11201, USA
| | - Seung Shin
- Othmer-Jacobs Department of Chemical and Biomolecular Engineering, New York University, 6 MetroTech Center, Brooklyn, NY 11201, USA
| | - Jin Ryoun Kim
- Othmer-Jacobs Department of Chemical and Biomolecular Engineering, New York University, 6 MetroTech Center, Brooklyn, NY 11201, USA
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4
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Kötzler MP, McIntosh LP, Withers SG. Refolding the unfoldable: A systematic approach for renaturation of Bacillus circulans xylanase. Protein Sci 2017; 26:1555-1563. [PMID: 28466501 DOI: 10.1002/pro.3181] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2017] [Revised: 04/22/2017] [Accepted: 04/24/2017] [Indexed: 11/11/2022]
Abstract
Xylanases are important polysaccharide-cleaving catalysts for the pulp and paper, animal feeds and biofuels industries. They have also proved to be valuable model systems for understanding enzymatic catalysis, with one of the best studied being the GH11 xylanase from Bacillus circulans (Bcx). However, proteins from this class are very recalcitrant to refolding in vitro. This both limits their high level expression in heterologous hosts, and prevents experimental approaches, such as peptide ligation or chemical modifications, to probe and engineer their stability and function. To solve this problem, a systematic screening approach was employed to identify suitable buffer conditions for renaturing Bcx in vitro. The fractional factorial screen employed identified starting conditions for refolding, which were then refined and developed into a generic protocol for renaturing preparative amounts of active Bcx in a 50-60% yield from inclusion bodies. The method is robust and proved equally proficient at refolding circularly permuted versions that carry cysteine mutations. This general approach should be applicable to related GH11 xylanases, as well as proteins adopting a similar β-jellyroll fold, that are otherwise recalcitrant to refolding in vitro.
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Affiliation(s)
- Miriam P Kötzler
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z1
| | - Lawrence P McIntosh
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z1.,Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z3.,Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z1
| | - Stephen G Withers
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z1.,Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z3.,Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z1
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5
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Kosciow K, Domin C, Schweiger P, Deppenmeier U. Extracellular targeting of an active endoxylanase by a TolB negative mutant of Gluconobacter oxydans. ACTA ACUST UNITED AC 2016; 43:989-99. [DOI: 10.1007/s10295-016-1770-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Accepted: 03/26/2016] [Indexed: 01/28/2023]
Abstract
Abstract
Gluconobacter (G.) oxydans strains have great industrial potential due to their ability to incompletely oxidize a wide range of carbohydrates. But there is one major limitation preventing their full production potential. Hydrolysis of polysaccharides is not possible because extracellular hydrolases are not encoded in the genome of Gluconobacter species. Therefore, as a first step for the generation of exoenzyme producing G. oxydans, a leaky outer membrane mutant was created by deleting the TolB encoding gene gox1687. As a second step the xynA gene encoding an endo-1,4-β-xylanase from Bacillus subtilis was expressed in G. oxydans ΔtolB. More than 70 % of the total XynA activity (0.91 mmol h−1 l culture−1) was detected in the culture supernatant of the TolB mutant and only 10 % of endoxylanase activity was observed in the supernatant of G. oxydans xynA. These results showed that a G. oxydans strain with an increased substrate spectrum that is able to use the renewable polysaccharide xylan as a substrate to produce the prebiotic compounds xylobiose and xylooligosaccharides was generated. This is the first report about the combination of the process of incomplete oxidation with the degradation of renewable organic materials from plants for the production of value-added products.
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Affiliation(s)
- Konrad Kosciow
- grid.10388.32 0000000122403300 Institute of Microbiology and Biotechnology University of Bonn Meckenheimer Allee 168 53115 Bonn Germany
| | - Claudia Domin
- grid.10388.32 0000000122403300 Institute of Microbiology and Biotechnology University of Bonn Meckenheimer Allee 168 53115 Bonn Germany
| | - Paul Schweiger
- grid.260126.1 0000000107458995 Biology Department Missouri State University 901 S. National Ave 65897 Springfield MO USA
| | - Uwe Deppenmeier
- grid.10388.32 0000000122403300 Institute of Microbiology and Biotechnology University of Bonn Meckenheimer Allee 168 53115 Bonn Germany
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6
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Kazuyo F, Hong SY, Yeon YJ, Joo JC, Yoo YJ. Enhancing the activity of Bacillus circulans xylanase by modulating the flexibility of the hinge region. J Ind Microbiol Biotechnol 2014; 41:1181-90. [PMID: 24849049 DOI: 10.1007/s10295-014-1454-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2013] [Accepted: 04/28/2014] [Indexed: 02/06/2023]
Abstract
Enzymes undergo multiple conformational changes in solution, and these dynamics are considered to play a critical role in enzyme activity. Hinge-bending motions, resulting from reciprocal movements of dynamical quasi-rigid bodies, are thought to be related to turnover rate and are affected by the physical properties of the hinge regions. In this study, hinge identification and flexibility modification of the regions by mutagenesis were conducted to explore the relationship between hinge flexibility and catalytic activity. Bacillus circulans xylanase was selected for the identification and mutation of the hinge regions. As a result, turnover rate (V(max)) was improved approximately twofold in mutants that have more rigid hinge structure, despite the decrease in K(m) and V(max)/K(m). This result indicates that the rigidly mutated hinge has positive effects on B. circulans xylanase activity.
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Affiliation(s)
- Fukura Kazuyo
- Graduate Program of Bioengineering, Seoul National University, Seoul, 151-742, Republic of Korea
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7
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Goswami GK, Krishnamohan M, Nain V, Aggarwal C, Ramesh B. Cloning and heterologous expression of cellulose free thermostable xylanase from Bacillus brevis. SPRINGERPLUS 2014; 3:20. [PMID: 25674425 PMCID: PMC4320173 DOI: 10.1186/2193-1801-3-20] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Accepted: 01/02/2014] [Indexed: 11/10/2022]
Abstract
Xylanase gene isolated from Bacillus brevis was expressed in E. coli BL21. Sequencing of the gene (Gen Bank accession number: HQ179986) showed that it belongs to family 11 xylanases. The recombinant xylanase was predominantly secreted to culture medium and showed mesophilic nature (optimum activity at 55°C and pH 7.0). The cell free culture medium exhibited 30 IU/ml xylanse activity. The enzyme did not show any cellulose activity and was active under wide range of temperature (40°C to 80°C) and pH (4 to 9). The enzyme showed considerable thermo stability and regained over 90% of activity, when returned to 55°C after boiling for 5 min. These physiochemical properties of B. brevis xylanse show high potential of its applications in paper and pulp industry.
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Affiliation(s)
- Girish K Goswami
- Amity Institute of Biotechnology, Amity University Rajasthan, Jaipur, 302001 India
| | | | - Vikrant Nain
- Department of Biotechnology, Gautam Buddha University, Greater NOIDA, 201308 India
| | - Chetana Aggarwal
- Division of Microbiology, Indian Agricultural Research Institute, New Delhi, 110012 India
| | - Bandarupalli Ramesh
- Department of Genetics and Plant Breeding, Ch. Charan Singh University, Meerut, 250004 India
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8
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Brockerman JA, Okon M, McIntosh LP. Detection and characterization of serine and threonine hydroxyl protons in Bacillus circulans xylanase by NMR spectroscopy. JOURNAL OF BIOMOLECULAR NMR 2014; 58:17-25. [PMID: 24306180 DOI: 10.1007/s10858-013-9799-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Accepted: 11/26/2013] [Indexed: 06/02/2023]
Abstract
Hydroxyl protons on serine and threonine residues are not well characterized in protein structures determined by both NMR spectroscopy and X-ray crystallography. In the case of NMR spectroscopy, this is in large part because hydroxyl proton signals are usually hidden under crowded regions of (1)H-NMR spectra and remain undetected by conventional heteronuclear correlation approaches that rely on strong one-bond (1)H-(15)N or (1)H-(13)C couplings. However, by filtering against protons directly bonded to (13)C or (15)N nuclei, signals from slowly-exchanging hydroxyls can be observed in the (1)H-NMR spectrum of a uniformly (13)C/(15)N-labeled protein. Here we demonstrate the use of a simple selective labeling scheme in combination with long-range heteronuclear scalar correlation experiments as an easy and relatively inexpensive way to detect and assign these hydroxyl proton signals. Using auxtrophic Escherichia coli strains, we produced Bacillus circulans xylanase (BcX) labeled with (13)C/(15)N-serine or (13)C/(15)N-threonine. Signals from two serine and three threonine hydroxyls in these protein samples were readily observed via (3)JC-OH couplings in long-range (13)C-HSQC spectra. These scalar couplings (~5-7 Hz) were measured in a sample of uniformly (13)C/(15)N-labeled BcX using a quantitative (13)C/(15)N-filtered spin-echo difference experiment. In a similar approach, the threonine and serine hydroxyl hydrogen exchange kinetics were measured using a (13)C/(15)N-filtered CLEANEX-PM pulse sequence. Collectively, these experiments provide insights into the structural and dynamic properties of several serine and threonine hydroxyls within this model protein.
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Affiliation(s)
- Jacob A Brockerman
- Department of Biochemistry and Molecular Biology, Life Sciences Centre, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada
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9
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Salamanca-Cardona L, Ashe CS, Stipanovic AJ, Nomura CT. Enhanced production of polyhydroxyalkanoates (PHAs) from beechwood xylan by recombinant Escherichia coli. Appl Microbiol Biotechnol 2013; 98:831-42. [DOI: 10.1007/s00253-013-5398-4] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2013] [Revised: 11/06/2013] [Accepted: 11/09/2013] [Indexed: 11/29/2022]
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10
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Ludwiczek ML, D’Angelo I, Yalloway GN, Brockerman JA, Okon M, Nielsen JE, Strynadka NCJ, Withers SG, McIntosh LP. Strategies for Modulating the pH-Dependent Activity of a Family 11 Glycoside Hydrolase. Biochemistry 2013; 52:3138-56. [DOI: 10.1021/bi400034m] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Martin L. Ludwiczek
- Department of Biochemistry and
Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
- Department of Chemistry, University of British Columbia, Vancouver, British
Columbia, Canada V6T 1Z1
- Michael Smith Laboratories, University of British Columbia, Vancouver, British
Columbia, Canada V6T 1Z4
| | - Igor D’Angelo
- Department of Biochemistry and
Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
| | - Gary N. Yalloway
- Department of Biochemistry and
Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
- Department of Chemistry, University of British Columbia, Vancouver, British
Columbia, Canada V6T 1Z1
| | - Jacob A. Brockerman
- Department of Biochemistry and
Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
- Department of Chemistry, University of British Columbia, Vancouver, British
Columbia, Canada V6T 1Z1
- Michael Smith Laboratories, University of British Columbia, Vancouver, British
Columbia, Canada V6T 1Z4
| | - Mark Okon
- Department of Biochemistry and
Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
- Department of Chemistry, University of British Columbia, Vancouver, British
Columbia, Canada V6T 1Z1
- Michael Smith Laboratories, University of British Columbia, Vancouver, British
Columbia, Canada V6T 1Z4
| | - Jens E. Nielsen
- School
of Biomolecular and Biomedical
Science, Centre for Synthesis and Chemical Biology, UCD Conway Institute, University College Dublin, Belfield, Dublin 4, Ireland
| | - Natalie C. J. Strynadka
- Department of Biochemistry and
Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
| | - Stephen G. Withers
- Department of Biochemistry and
Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
- Department of Chemistry, University of British Columbia, Vancouver, British
Columbia, Canada V6T 1Z1
- Centre for High-throughput Biology, University of British Columbia, Vancouver, British
Columbia, Canada V6T 1Z4
| | - Lawrence P. McIntosh
- Department of Biochemistry and
Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
- Department of Chemistry, University of British Columbia, Vancouver, British
Columbia, Canada V6T 1Z1
- Michael Smith Laboratories, University of British Columbia, Vancouver, British
Columbia, Canada V6T 1Z4
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11
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12
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Kim T, Joo JC, Yoo YJ. Hydrophobic interaction network analysis for thermostabilization of a mesophilic xylanase. J Biotechnol 2012; 161:49-59. [PMID: 22642881 DOI: 10.1016/j.jbiotec.2012.04.015] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2011] [Revised: 04/12/2012] [Accepted: 04/16/2012] [Indexed: 11/16/2022]
Abstract
One widely known drawback of enzymes is their instability in diverse conditions. The thermostability of enzymes is particularly relevant for industrial applications because operation at high temperatures has the advantage of a faster reaction rate. Protein stability is mainly determined in this study by intra-molecular hydrophobic interactions that have a collective and 3-dimensional clustering effect. To interpret the thermostability of enzymes, network analysis was introduced into the protein structure, and a network parameter of structural hierarchy, k of k-clique, was used to discern more developed hydrophobic interaction clusters in the protein structure. The favorable clustering conformations of hydrophobic residues, which seemed to be important for protein thermostability, were discovered by the application of a network analysis to hydrophobic interactions of GH11 xylanases. Coordinating higher k-clique hydrophobic interaction clusters through the site-directed mutagenesis of the model enzyme, Bacillus circulans xylanase, stabilized the local structure and thus improved thermostability, such that the enzyme half-life and melting temperature increased by 78 fold and 8.8 °C, respectively. This study highlights the advantages of interpreting collective hydrophobic interaction patterns and their structural hierarchy and the possibility of applying network analysis to the thermostabilization of enzymes.
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Affiliation(s)
- Taeho Kim
- Interdisciplinary Program of Bioengineering, Seoul National University, Seoul 151-744, Republic of Korea
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13
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Goddard-Borger ED, Fiege B, Kwan EM, Withers SG. Glycosynthase-Mediated Assembly of Xylanase Substrates and Inhibitors. Chembiochem 2011; 12:1703-11. [DOI: 10.1002/cbic.201100229] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2011] [Indexed: 11/09/2022]
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14
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Joo JC, Pack SP, Kim YH, Yoo YJ. Thermostabilization of Bacillus circulans xylanase: computational optimization of unstable residues based on thermal fluctuation analysis. J Biotechnol 2010; 151:56-65. [PMID: 20959126 DOI: 10.1016/j.jbiotec.2010.10.002] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Revised: 10/01/2010] [Accepted: 10/07/2010] [Indexed: 10/18/2022]
Abstract
Low thermostability often hampers the applications of xylanases in industrial processes operated at high temperature, such as degradation of biomass or pulp bleaching. Thermostability of enzymes can be improved by the optimization of unstable residues via protein engineering. In this study, computational modeling instead of random mutagenesis was used to optimize unstable residues of Bacillus circulans xylanase (Bcx). The thermal fluctuations of unstable residues known as important to the thermal unfolding of Bcx were investigated by the molecular dynamics (MD) simulations at 300 K and 330 K to identify promising residues. The N52 site in unstable regions showed the highest thermal fluctuations. Subsequently, computational design was conducted to predict the optimal sequences of unstable residues. Five optimal single mutants were predicted by the computational design, and the N52Y mutation showed the thermostabilization effect. The N52 residue is conserved in Bacillus species xylanases and the structure analysis revealed that the N52Y mutation introduced more hydrophobic clusters for thermostability, as well as a more favorable aromatic stacking environment for substrate binding. We confirm that flexible residues at high temperature in unstable regions can be promising targets to improve thermostability of enzymes.
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Affiliation(s)
- Jeong Chan Joo
- School of Chemical and Biological Engineering, Seoul National University, Seoul 151-744, Republic of Korea
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15
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Jollymore A, Li H. Measuring “Unmeasurable” Folding Kinetics of Proteins by Single-Molecule Force Spectroscopy. J Mol Biol 2010; 402:610-7. [DOI: 10.1016/j.jmb.2010.07.059] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2010] [Revised: 07/29/2010] [Accepted: 07/29/2010] [Indexed: 10/19/2022]
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16
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Reitinger S, Yu Y, Wicki J, Ludwiczek M, D’Angelo I, Baturin S, Okon M, Strynadka NCJ, Lutz S, Withers SG, McIntosh LP. Circular Permutation of Bacillus circulans Xylanase: A Kinetic and Structural Study. Biochemistry 2010; 49:2464-74. [DOI: 10.1021/bi100036f] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Stephan Reitinger
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
- Centre for High Throughput Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
| | - Ying Yu
- Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322
| | - Jacqueline Wicki
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
- Centre for High Throughput Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
| | - Martin Ludwiczek
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
| | - Igor D’Angelo
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
| | - Simon Baturin
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
| | - Mark Okon
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
| | - Natalie C. J. Strynadka
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
- Michael Smith Laboratory, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
- Centre for Blood Research, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
| | - Stefan Lutz
- Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322
| | - Stephen G. Withers
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
- Centre for High Throughput Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
| | - Lawrence P. McIntosh
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
- Centre for High Throughput Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
- Michael Smith Laboratory, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
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17
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Ruller R, Deliberto L, Ferreira TL, Ward RJ. Thermostable variants of the recombinant xylanase a from Bacillus subtilis produced by directed evolution show reduced heat capacity changes. Proteins 2007; 70:1280-93. [PMID: 17876824 DOI: 10.1002/prot.21617] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Directed evolution techniques have been used to improve the thermal stability of the xylanase A from Bacillus subtilis (XylA). Two generations of random mutant libraries generated by error prone PCR coupled with a single generation of DNA shuffling produced a series of mutant proteins with increasing thermostability. The most Thermostable XylA variant from the third generation contained four mutations Q7H, G13R, S22P, and S179C that showed an increase in melting temperature of 20 degrees C. The thermodynamic properties of a representative subset of nine XylA variants showing a range of thermostabilities were measured by thermal denaturation as monitored by the change in the far ultraviolet circular dichroism signal. Analysis of the data from these thermostable variants demonstrated a correlation between the decrease in the heat capacity change (deltaC(p)) with an increase in the midpoint of the transition temperature (T(m)) on transition from the native to the unfolded state. This result could not be interpreted within the context of the changes in accessible surface area of the protein on transition from the native to unfolded states. Since all the mutations are located at the surface of the protein, these results suggest that an explanation of the decrease in deltaC(p) should include effects arising from the protein/solvent interface.
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Affiliation(s)
- Roberto Ruller
- Departamento de Biologia Celular e Molecular e Bioagentes Patogênicos, FMRP-USP, Ribeirão Preto-SP, Universidade de São Paulo, São Paulo, Brazil
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18
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Ludwiczek ML, Heller M, Kantner T, McIntosh LP. A secondary xylan-binding site enhances the catalytic activity of a single-domain family 11 glycoside hydrolase. J Mol Biol 2007; 373:337-54. [PMID: 17822716 DOI: 10.1016/j.jmb.2007.07.057] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2007] [Accepted: 07/24/2007] [Indexed: 11/20/2022]
Abstract
Bacillus circulans xylanase (BcX) is a single-domain family 11 glycoside hydrolase. Using NMR-monitored titrations, we discovered that an inactive variant of this enzyme, E78Q-BcX, bound xylooligosaccharides not only within its pronounced active site (AS) cleft, but also at a distal surface region. Chemical shift perturbation mapping and affinity electrophoresis, combined with mutational studies, identified the xylan-specific secondary binding site (SBS) as a shallow groove lined by Asn, Ser, and Thr residues and with a Trp at one end. The AS and SBS bound short xylooligosaccharides with similar dissociation constants in the millimolar range. However, the on and off-rates to the SBS were at least tenfold faster than those of kon approximately 3x10(5) M(-1) s(-1) and koff approximately 1000 s(-1) measured for xylotetraose to the AS of E78Q-BcX. Consistent with their structural differences, this suggests that a conformational change in the enzyme and/or the substrate is required for association to and dissociation from the deep AS, but not the shallow SBS. In contrast to the independent binding of small xylooligosaccharides, high-affinity binding of soluble and insoluble xylan, as well as xylododecaose, occurred cooperatively to the two sites. This was evidenced by an approximately 100-fold increase in relative Kd values for these ligands upon mutation of the SBS. The SBS also enhances the activity of BcX towards soluble and insoluble xylan through a significant reduction in the Michaelis KM values for these polymeric substrates. This study provides an unexpected example of how a single domain family 11 xylanase overcomes the lack of a carbohydrate-binding module through the use of a secondary binding site to enhance substrate specificity and affinity.
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Affiliation(s)
- Martin L Ludwiczek
- Department of Biochemistry and Molecular Biology, Department of Chemistry, The Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
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19
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Miyazaki K, Takenouchi M, Kondo H, Noro N, Suzuki M, Tsuda S. Thermal stabilization of Bacillus subtilis family-11 xylanase by directed evolution. J Biol Chem 2006; 281:10236-42. [PMID: 16467302 DOI: 10.1074/jbc.m511948200] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We used directed evolution to enhance the thermostability of glycosyl hydrolase family-11 xylanase from Bacillus subtilis. By combining random point mutagenesis, saturation mutagenesis, and DNA shuffling, a thermostable variant, Xyl(st), was identified which contained three amino acid substitutions: Q7H, N8F, and S179C. The half-inactivation temperature (the midpoint of the melting curves) for the Xyl(st) variant compared with the wild-type enzyme after incubation for 10 min was elevated from 58 to 68 degrees C. At 60 degrees C the wild-type enzyme was inactivated within 5 min, but Xyl(st) retained full activity for at least 2 h. The stabilization was accompanied by evidence of thermophilicity; that is, an increase in the optimal reaction temperature from 55 to 65 degrees C and lower activity at low temperatures and higher activity at higher temperatures relative to wild type. To elucidate the mechanism of thermal stabilization, three-dimensional structures were determined for the wild-type and Xyl(st) enzymes. A cavity was identified around Gln-7/Asn-8 in wild type that was filled with bulky, hydrophobic residues in Xyl(st). This site was not identified by previous approaches, but directed evolution identified the region as a weak point. Formation of an intermolecular disulfide bridge via Cys-179 was observed between monomers in Xyl(st). However, the stability was essentially the same in the presence and absence of a reducing agent, indicating that the increased hydrophobicity around the Cys-179 accounted for the stability.
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Affiliation(s)
- Kentaro Miyazaki
- Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan.
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20
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Beliën T, Hertveldt K, Van den Brande K, Robben J, Van Campenhout S, Volckaert G. Functional display of family 11 endoxylanases on the surface of phage M13. J Biotechnol 2005; 115:249-60. [PMID: 15639087 DOI: 10.1016/j.jbiotec.2004.08.013] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2003] [Revised: 08/06/2004] [Accepted: 08/19/2004] [Indexed: 01/08/2023]
Abstract
Two family 11 endoxylanases (EC 3.2.1.8) were functionally displayed on the surface of bacteriophage M13. The genes encoding endo-1,4-xylanase I from Aspergillus niger (ExlA) and endo-1,4-xylanase A from Bacillus subtilis (XynA) were fused to the gene encoding the minor coat protein g3p in phagemid vector pHOS31. Phage rescue resulted in functional monovalent display of the enzymes as was demonstrated by three independent tests. Firstly, purified recombinant phage particles showed a clear hydrolytic activity in an activity assay based on insoluble, chromagenic arabinoxylan substrate. Secondly, specific binding of endoxylanase displaying phages to immobilized endoxylanase inhibitors was demonstrated by interaction ELISA. Finally, two rounds of selection and amplification in a biopanning procedure against immobilized endoxylanase inhibitor were performed. Phages displaying endoxylanases were strongly enriched from background phages displaying unrelated proteins. These results open perspectives to use phage display for analysing protein-protein interactions at the interface between endoxylanases and their inhibitors. In addition, this technology should enable engineering of endoxylanases into novel variants with altered binding properties towards endoxylanase inhibitors.
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Affiliation(s)
- T Beliën
- Laboratory of Gene Technology, Katholieke Universiteit Leuven, Kasteelpark Arenberg 21, B-3001 Leuven, Belgium
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21
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Poon DKY, Webster P, Withers SG, McIntosh LP. Characterizing the pH-dependent stability and catalytic mechanism of the family 11 xylanase from the alkalophilic Bacillus agaradhaerens. Carbohydr Res 2003; 338:415-21. [PMID: 12559743 DOI: 10.1016/s0008-6215(02)00486-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The xylanase, BadX, from the alkalophilic Bacillus agaradhaerens was cloned, expressed and studied in comparison to a related family 11 xylanase, BcX, from B. circulans. Despite the alkaline versus neutral conditions under which these bacteria grow, BadX and BcX both exhibit optimal activity near pH 5.6 using the substrate o-nitrophenyl beta-xylobioside. Analysis of the bell-shaped activity profile of BadX yielded apparent pK(a) values of 4.2 and 7.1, assignable to its nucleophile Glu94 and general acid Glu184, respectively. In addition to having an approximately 10-fold higher k(cat)/K(m) value with this substrate at pH 6 and 40 degrees C, BadX has significantly higher thermal stability than BcX under neutral and alkaline conditions. This enhanced stability, rather than a shift in its pH-optimum, may allow BadX to hydrolyze xylan under conditions of elevated temperature and pH.
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Affiliation(s)
- David K Y Poon
- The Department of Chemistry, University of British Columbia, BC, V6T 1Z1, Vancouver, Canada
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22
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Subramaniyan S, Prema P. Biotechnology of microbial xylanases: enzymology, molecular biology, and application. Crit Rev Biotechnol 2002; 22:33-64. [PMID: 11958335 DOI: 10.1080/07388550290789450] [Citation(s) in RCA: 339] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Xylanases are hydrolases depolymerizing the plant cell wall component xylan, the second most abundant polysaccharide. The molecular structure and hydrolytic pattern of xylanases have been reported extensively and the mechanism of hydrolysis has also been proposed. There are several models for the gene regulation of which this article could add to the wealth of knowledge. Future work on the application of these enzymes in the paper and pulp, food industry, in environmental science, that is, bio-fueling, effluent treatment, and agro-waste treatment, etc. require a complete understanding of the functional and genetic significance of the xylanases. However, the thrust area has been identified as the paper and pulp industry. The major problem in the field of paper bleaching is the removal of lignin and its derivatives, which are linked to cellulose and xylan. Xylanases are more suitable in the paper and pulp industry than lignin-degrading systems.
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Affiliation(s)
- S Subramaniyan
- Biochemical Processing Division, Regional Research Laboratory (CSIR), Trivandrum, India
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23
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Joshi MD, Sidhu G, Pot I, Brayer GD, Withers SG, McIntosh LP. Hydrogen bonding and catalysis: a novel explanation for how a single amino acid substitution can change the pH optimum of a glycosidase. J Mol Biol 2000; 299:255-79. [PMID: 10860737 DOI: 10.1006/jmbi.2000.3722] [Citation(s) in RCA: 181] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The pH optima of family 11 xylanases are well correlated with the nature of the residue adjacent to the acid/base catalyst. In xylanases that function optimally under acidic conditions, this residue is aspartic acid, whereas it is asparagine in those that function under more alkaline conditions. Previous studies of wild-type (WT) Bacillus circulans xylanase (BCX), with an asparagine residue at position 35, demonstrated that its pH-dependent activity follows the ionization states of the nucleophile Glu78 (pKa 4.6) and the acid/base catalyst Glu172 (pKa 6.7). As predicted from sequence comparisons, substitution of this asparagine residue with an aspartic acid residue (N35D BCX) shifts its pH optimum from 5.7 to 4.6, with an approximately 20% increase in activity. The bell-shaped pH-activity profile of this mutant enzyme follows apparent pKa values of 3.5 and 5.8. Based on 13C-NMR titrations, the predominant pKa values of its active-site carboxyl groups are 3.7 (Asp35), 5.7 (Glu78) and 8.4 (Glu172). Thus, in contrast to the WT enzyme, the pH-activity profile of N35D BCX appears to be set by Asp35 and Glu78. Mutational, kinetic, and structural studies of N35D BCX, both in its native and covalently modified 2-fluoro-xylobiosyl glycosyl-enzyme intermediate states, reveal that the xylanase still follows a double-displacement mechanism with Glu78 serving as the nucleophile. We therefore propose that Asp35 and Glu172 function together as the general acid/base catalyst, and that N35D BCX exhibits a "reverse protonation" mechanism in which it is catalytically active when Asp35, with the lower pKa, is protonated, while Glu78, with the higher pKa, is deprotonated. This implies that the mutant enzyme must have an inherent catalytic efficiency at least 100-fold higher than that of the parental WT, because only approximately 1% of its population is in the correct ionization state for catalysis at its pH optimum. The increased efficiency of N35D BCX, and by inference all "acidic" family 11 xylanases, is attributed to the formation of a short (2.7 A) hydrogen bond between Asp35 and Glu172, observed in the crystal structure of the glycosyl-enzyme intermediate of this enzyme, that will substantially stabilize the transition state for glycosyl transfer. Such a mechanism may be much more commonly employed than is generally realized, necessitating careful analysis of the pH-dependence of enzymatic catalysis.
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Affiliation(s)
- M D Joshi
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, Canada
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24
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Abstract
Hemicellulolytic microorganisms play a significant role in nature by recycling hemicellulose, one of the main components of plant polysaccharides. Xylanases (EC 3.2.1.8) catalyze the hydrolysis of xylan, the major constituent of hemicellulose. The use of these enzymes could greatly improve the overall economics of processing lignocellulosic materials for the generation of liquid fuels and chemicals. Recently cellulase-free xylanases have received great attention in the development of environmentally friendly technologies in the paper and pulp industry. In microorganisms that produce xylanases low molecular mass fragments of xylan and their positional isomers play a key role in regulating its biosynthesis. Xylanase and cellulase production appear to be regulated separately, although the pleiotropy of mutations, which causes the elimination of both genes, suggests some linkage in the synthesis of the two enzymes. Xylanases are found in a cornucopia of organisms and the genes encoding them have been cloned in homologous and heterologous hosts with the objectives of overproducing the enzyme and altering its properties to suit commercial applications. Sequence analyses of xylanases have revealed distinct catalytic and cellulose binding domains, with a separate non-catalytic domain that has been reported to confer enhanced thermostability in some xylanases. Analyses of three-dimensional structures and the properties of mutants have revealed the involvement of specific tyrosine and tryptophan residues in the substrate binding site and of glutamate and aspartate residues in the catalytic mechanism. Many lines of evidence suggest that xylanases operate via a double displacement mechanism in which the anomeric configuration is retained, although some of the enzymes catalyze single displacement reactions with inversion of configuration. Based on a dendrogram obtained from amino acid sequence similarities the evolutionary relationship between xylanases is assessed. In addition the properties of xylanases from extremophilic organisms have been evaluated in terms of biotechnological applications.
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Affiliation(s)
- N Kulkarni
- Division of Biochemical Sciences, National Chemical Laboratory, Pune, India
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25
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Davoodi J, Wakarchuk WW, Surewicz WK, Carey PR. Scan-rate dependence in protein calorimetry: the reversible transitions of Bacillus circulans xylanase and a disulfide-bridge mutant. Protein Sci 1998; 7:1538-44. [PMID: 9684886 PMCID: PMC2144070 DOI: 10.1002/pro.5560070707] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The stabilities of Bacillus circulans xylanase and a disulfide-bridge-containing mutant (S100C/N148C) were investigated by differential scanning calorimetry (DSC) and thermal inactivation kinetics. The thermal denaturation of both proteins was found to be irreversible, and the apparent transition temperatures showed a considerable dependence upon scanning rate. In the presence of low (nondenaturing) concentrations of urea, calorimetric transitions were observed for both proteins in the second heating cycle, indicating reversible denaturation occurs under those conditions. However, even for these reversible processes, the DSC curves for the wild-type protein showed a scan-rate dependence that was similar to that in the absence of urea. Calorimetric thermograms for the disulfide mutant were significantly less scan-rate dependent in the presence of urea than in the urea-free buffer. The present data show that, just as for irreversible transitions, the apparent transition temperature for the reversible denaturation of proteins can be scan-rate dependent, confirming the prediction of Lepock et al. (Lepock JR, Rithcie KP, Kolios MC, Rodahl AM, Heinz KA, Kruuf J, 1992, Biochemistry 31:12706-12712). The kinetic factors responsible for scan-rate dependence may lead to significant distortions and asymmetry of endotherms, especially at higher scanning rates. This points to the need to check for scan-rate dependence, even in the case of reversible denaturation, before any attempt is made to analyze asymmetric DSC curves by standard thermodynamic procedures. Experiments with the disulfide-bridge-containing mutant indicate that the introduction of the disulfide bond provides additional stabilization of xylanase by changing the rate-limiting step on the thermal denaturation pathway.
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Affiliation(s)
- J Davoodi
- Department of Biochemistry, University of Ottawa, Ontario, Canada
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26
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Joshi MD, Hedberg A, McIntosh LP. Complete measurement of the pKa values of the carboxyl and imidazole groups in Bacillus circulans xylanase. Protein Sci 1997; 6:2667-70. [PMID: 9416621 PMCID: PMC2143618 DOI: 10.1002/pro.5560061224] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Electrostatic interactions in proteins can be dissected experimentally by determining the pKa values of their constituent ionizable amino acids. To complement previous studies of the glutamic acid and histidine residues in Bacillus circulans xylanase (BCX), we have used NMR methods to measure the pKa s of the seven aspartic acids and the C-terminus of this protein. The pKa s of these carboxyls are all less than the corresponding values observed with random coil polypeptides, indicating that their ionization contributes favorably to the stability of the folded enzyme. In general, the aspartic acids with the most reduced pKa s are those with limited exposure to the solvent and a high degree of conservation among homologous xylanases. Most dramatically, Asp 83 and Asp 101 have pKa s < 2 and thus remain deprotonated in native BCX under all conditions examined. Asp 83 is completely buried, forming a strong salt bridge with Arg 136. In contrast, Asp 101 is located on the surface of the protein, stabilized in the deprotonated form by an extensive network of hydrogen bonds involving an internal water molecule and the neutral side-chain and main-chain atoms of Ser 100 and Thr 145. These data provide a complete experimental database for theoretical studies of the ionization behavior of BCX under acidic conditions.
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Affiliation(s)
- M D Joshi
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, Canada
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27
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Plesniak LA, Connelly GP, Wakarchuk WW, McIntosh LP. Characterization of a buried neutral histidine residue in Bacillus circulans xylanase: NMR assignments, pH titration, and hydrogen exchange. Protein Sci 1996; 5:2319-28. [PMID: 8931150 PMCID: PMC2143293 DOI: 10.1002/pro.5560051118] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Bacillus circulans xylanase contains two histidines, one of which (His 156) is solvent exposed, whereas the other (His 149) is buried within its hydrophobic core. His 149 is involved in a network of hydrogen bonds with an internal water and Ser 130, as well as a potential weak aromatic-aromatic interaction with Tyr 105. These three residues, and their network of interactions with the bound water, are conserved in four homologous xylanases. To probe the structural role played by His 149, NMR spectroscopy was used to characterize the histidines in BCX. Complete assignments of the 1H, 13C, and 15N resonances and tautomeric forms of the imidazole rings were obtained from two-dimensional heteronuclear correlation experiments. An unusual spectroscopic feature of BCX is a peak near 12 ppm arising from the nitrogen bonded 1H epsilon 2 of His 149. Due to its solvent inaccessibility and hydrogen bonding to an internal water molecule, the exchange rate of this proton (4.0 x 10(-5) s-1 at pH*7.04 and 30 degrees C) is retarded by > 10(6)-fold relative to an exposed histidine. The pKa of His 156 is unperturbed at approximately 6.5, as measured from the pH dependence of the 15N- and 1H-NMR spectra of BCX. In contrast, His 149 has a pKa < 2.3, existing in the neutral N epsilon 2H tautomeric state under all conditions examined. BCX unfolds at low pH and 30 degrees C, and thus His 149 is never protonated significantly in the context of the native enzyme. The structural importance of this buried histidine is confirmed by the destablizing effect of substituting a phenylalanine or glutamine at position 149 in BCX.
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Affiliation(s)
- L A Plesniak
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, Canada
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28
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Plesniak LA, Wakarchuk WW, McIntosh LP. Secondary structure and NMR assignments of Bacillus circulans xylanase. Protein Sci 1996; 5:1118-35. [PMID: 8762143 PMCID: PMC2143425 DOI: 10.1002/pro.5560050614] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Bacillus circulans xylanase (BCX) is a member of the family of low molecular weight endo-beta-(1,4)-xylanases. The main-chain 1H, 13C, and 15N resonances of this 20.4-kDa enzyme were assigned using heteronuclear NMR experiments recorded on a combination of selectively and uniformly labeled protein samples. Using chemical shift, NOE, J coupling, and amide hydrogen exchange information, 14 beta-strands, arranged in a network of three beta-sheets, and a single alpha-helix were identified in BCX. The NMR-derived secondary structure and beta-sheet topology agree closely with that observed in the crystal structure of this protein. The HN of Ile 118 has a strongly upfield-shifted resonance at 4.03 ppm, indicative of a potential amide-aromatic hydrogen bond to the indole ring of Trp 71. This interaction, which is conserved in all low molecular weight xylanases of known structure, may play an important role in establishing the active site conformation of these enzymes. Following hen egg white and bacteriophage T4 lysozymes, B. circulans xylanase represents the third family of beta-glycanases for which extensive NMR assignments have been reported. These assignments provide the background for detailed studies of the mechanism of carbohydrate recognition and hydrolysis by this bacterial xylanase.
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Affiliation(s)
- L A Plesniak
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, Canada
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29
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Ziser L, Setyawati I, Withers SG. Syntheses and testing of substrates and mechanism-based inactivators for xylanases. Carbohydr Res 1995; 274:137-53. [PMID: 7585703 DOI: 10.1016/0008-6215(95)00080-d] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The syntheses of the 2,5- and 3,4-dinitrophenyl beta-xylobiosides by two separate routes are described, as well as the syntheses of the 2,4-dinitrophenyl beta-glycosides of 2-chloro-2-deoxy-xylobiose and 2-deoxy-2-fluoro-xylobiose. Both the 3,4- and 2,5-dinitrophenyl beta-xylobiosides proved to be good substrates for the Bacillus subtilis xylanase, with kcat/Km values of 1.0 and 34.4 mM-1 s-1, respectively. Excellent time-dependent inactivation of the exoxylanase/glucanase from Cellulomonas fimi was provided by 2,4-dinitrophenyl 2-deoxy-2-fluoro-beta-xylobioside, according to inactivation parameters of ki = 0.057 min-1 and Ki = 0.0035 mM.
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Affiliation(s)
- L Ziser
- Department of Chemistry, University of British Columbia, Vancouver, Canada
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30
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Sung WL, Luk CK, Chan B, Wakarchuk W, Yaguchi M, Campbell R, Willick G, Ishikawa K, Zahab DM. Expression of Trichoderma reesei and Trichoderma viride xylanases in Escherichia coli. Biochem Cell Biol 1995; 73:253-9. [PMID: 8829371 DOI: 10.1139/o95-031] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Synthetic genes encoding the 190 amino acid Trichoderma reesei xylanase II (TrX) and the closely related Trichoderma viride xylanases have been synthesized in a two-step procedure. Initially, a partial gene encoding amino acids 92-190 was constructed in fusion with the N-terminal half of the Bacillus circulans xylanase (BcX). The remaining BcX gene sequence was replaced during the assembly of the coding sequence for amino acids 1-91. Expression of the synthetic genes in Escherichia coli yielded recombinant xylanases with specific activity generally identical with the natural TrX. However, the recombinant TrX showed thermostability and temperature optimum lower than those of the natural TrX, thus indicating that the posttranslational modifications of the latter in its fungal host are essential to its greater stability. A mutation N19K further decreased the thermostability of the recombinant TrX.
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Affiliation(s)
- W L Sung
- Institute for Biological Sciences, National Research Council of Canada, Ottawa, ON, Canada
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31
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Wakarchuk WW, Campbell RL, Sung WL, Davoodi J, Yaguchi M. Mutational and crystallographic analyses of the active site residues of the Bacillus circulans xylanase. Protein Sci 1994; 3:467-75. [PMID: 8019418 PMCID: PMC2142693 DOI: 10.1002/pro.5560030312] [Citation(s) in RCA: 245] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Using site-directed mutagenesis we have investigated the catalytic residues in a xylanase from Bacillus circulans. Analysis of the mutants E78D and E172D indicated that mutations in these conserved residues do not grossly alter the structure of the enzyme and that these residues participate in the catalytic mechanism. We have now determined the crystal structure of an enzyme-substrate complex to 108 A resolution using a catalytically incompetent mutant (E172C). In addition to the catalytic residues, Glu 78 and Glu 172, we have identified 2 tyrosine residues, Tyr 69 and Tyr 80, which likely function in substrate binding, and an arginine residue, Arg 112, which plays an important role in the active site of this enzyme. On the basis of our work we would propose that Glu 78 is the nucleophile and that Glu 172 is the acid-base catalyst in the reaction.
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Affiliation(s)
- W W Wakarchuk
- Institute for Biological Sciences, National Research Council of Canada, Ottawa, Ontario
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