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Lee J, Dalton RA, Dennison C. Copper delivery to an endospore coat protein of Bacillus subtilis. Front Cell Dev Biol 2022; 10:916114. [PMID: 36133923 PMCID: PMC9484137 DOI: 10.3389/fcell.2022.916114] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Accepted: 07/26/2022] [Indexed: 11/13/2022] Open
Abstract
A family of cytosolic copper (Cu) storage proteins (the Csps) bind large quantities of Cu(I) via their Cys-lined four-helix bundles, and the majority are cytosolic (Csp3s). The presence of Csp3s in many bacteria appears inconsistent with the current dogma that bacteria, unlike eukaryotes, have evolved not to maintain intracellular pools of Cu due to its potential toxicity. Sporulation in Bacillus subtilis has been used to investigate if a Csp3 binds Cu(I) in the cytosol for a target enzyme. The activity of the Cu-requiring endospore multi-Cu oxidase BsCotA (a laccase) increases under Cu-replete conditions in wild type B. subtilis. In the strain lacking BsCsp3 lower BsCotA activity is observed and is unaffected by Cu levels. BsCsp3 loaded with Cu(I) readily activates apo-BsCotA in vitro. Experiments with a high affinity Cu(I) chelator demonstrate that Cu(I) transfer from Cu(I)-BsCsp3 must occur via an associative mechanism. BsCsp3 and BsCotA are both upregulated during late sporulation. We hypothesise that BsCsp3 acquires cuprous ions in the cytosol of B. subtilis for BsCotA.
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2
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Choolaei Z, Flick R, Khusnutdinova AN, Edwards EA, Yakunin AF. Lignin-oxidizing activity of bacterial laccases characterized using soluble substrates and polymeric lignin. J Biotechnol 2020; 325:128-137. [PMID: 33186661 DOI: 10.1016/j.jbiotec.2020.11.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Revised: 10/21/2020] [Accepted: 11/03/2020] [Indexed: 12/11/2022]
Abstract
Efficient biotransformation of lignin requires the activity of different oxidative enzymes. In this work, 19 bacterial multi-copper oxidases were screened for oxidase activity against 19 soluble substrates and revealed the highest activity in the laccase CotABsu (BSU0630) from Bacillus subtilis. Structure-based site-directed mutagenesis of CotABsu identified four conserved residues (His419, Cys492, His497, and Met502) as critical for activity against 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate) (ABTS). Greatly reduced oxidase activity was found in the CotABsu mutant proteins E213A, N214A, C229A, N264A, E298A, T415A, R416A, Q468A, and T480A. We also designed a lignin-agarose plate screen for detecting oxidase activity of purified proteins against polymeric lignin, which confirmed the results obtained with ABTS and identified three mutant variants with increased activity toward kraft lignin (E213A, T415A, and T260A). X-ray photoelectron spectroscopy analysis of low sulfonate kraft lignin after incubation with CotABsu revealed a reduction in the content of CC/CC bonds and increase in CO/CO bonds. Product analyses using mass spectrometry, liquid chromatography, and bright-field microscopy revealed an increased polymerization state of reaction products suggesting that formation of radical intermediates was followed by radical coupling. Our results provide further insights into the mechanisms of lignin oxidation by laccases.
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Affiliation(s)
- Zahra Choolaei
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario M5S 3E5, Canada
| | - Robert Flick
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario M5S 3E5, Canada
| | - Anna N Khusnutdinova
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario M5S 3E5, Canada
| | - Elizabeth A Edwards
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario M5S 3E5, Canada
| | - Alexander F Yakunin
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario M5S 3E5, Canada; Centre for Environmental Biotechnology, School of Natural Sciences, Bangor University, Bangor, LL57 2UW, UK.
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Nakhaee N, Asad S, Khajeh K, Arab SS, Amoozegar MA. Improving the thermal stability of azoreductase from Halomonas elongata by introducing a disulfide bond via site-directed mutagenesis. Biotechnol Appl Biochem 2018; 65:883-891. [PMID: 30132989 DOI: 10.1002/bab.1688] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Accepted: 08/11/2018] [Indexed: 11/06/2022]
Abstract
Azoreductases mainly reduce azo dyes, the largest class of colorants, to colorless aromatic amines. AzoH, a new azoreductase from the halophilic bacterium, Halomonas elongata, has been recently cloned and expressed in Escherichia coli. The aim of this study was to improve thermal stability of this enzyme by introducing new disulfide bonds. Since X-ray crystallography was not available, homology modeling and molecular dynamics was used to construct the enzyme three-dimensional structure. Potential disulfide bonds for increasing thermal stability were found using DIScover online software. Appropriate mutations (L49C/D108C) to form a disulfide bond were introduced by the Quik-Change method. Mutant protein expressed in E. coli showed increased thermal stability at 50 °C (increased half-life from 12.6 Min in AzoH to 26.66 Min in a mutated enzyme). The mutated enzyme could also tolerate 5% (w/v) NaCl and retained 30% of original activity after 24 H incubation, whereas the wild-type enzyme was completely inactivated. According to circular dichroism studies, the secondary structure was not altered by this mutation; however, a blue shift in intrinsic florescent graph revealed changes in the tertiary structure. This is the first study to improve thermal stability and salt tolerance of a halophilic azoreductase.
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Affiliation(s)
- Narjes Nakhaee
- Department of Biotechnology, College of Science, University of Tehran, Tehran, Iran
| | - Sedigheh Asad
- Department of Biotechnology, College of Science, University of Tehran, Tehran, Iran
| | - Khosro Khajeh
- Department of Biochemistry, Faculty of Biological Sciences, Tarbiat Modares University, Tehran, Iran
| | - Seyed Shahriar Arab
- Department of Biophysics, Faculty of Biological Sciences, Tarbiat Modares University, Tehran, Iran
| | - Mohammad Ali Amoozegar
- Extremophiles Laboratory, Department of Microbiology, School of Biology and Center of Excellence in Phylogeny of Living Organisms, College of Science, University of Tehran, Tehran, Iran
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Increasing the catalytic activity of Bilirubin oxidase from Bacillus pumilus: Importance of host strain and chaperones proteins. J Biotechnol 2016; 230:19-25. [PMID: 27165502 DOI: 10.1016/j.jbiotec.2016.04.035] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2015] [Revised: 04/12/2016] [Accepted: 04/19/2016] [Indexed: 02/02/2023]
Abstract
Aggregation of recombinant proteins into inclusion bodies (IBs) is the main problem of the expression of multicopper oxidase in Escherichia coli. It is usually attributed to inefficient folding of proteins due to the lack of copper and/or unavailability of chaperone proteins. The general strategies reported to overcome this issue have been focused on increasing the intracellular copper concentration. Here we report a complementary method to optimize the expression in E. coli of a promising Bilirubin oxidase (BOD) isolated from Bacillus pumilus. First, as this BOD has a disulfide bridge, we switched E.coli strain from BL21 (DE3) to Origami B (DE3), known to promote the formation of disulfide bridges in the bacterial cytoplasm. In a second step, we investigate the effect of co-expression of chaperone proteins on the protein production and specific activity. Our strategy allowed increasing the final amount of enzyme by 858% and its catalytic rate constant by 83%.
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5
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Niu C, Zhu L, Xu X, Li Q. Rational Design of Disulfide Bonds Increases Thermostability of a Mesophilic 1,3-1,4-β-Glucanase from Bacillus terquilensis. PLoS One 2016; 11:e0154036. [PMID: 27100881 PMCID: PMC4839689 DOI: 10.1371/journal.pone.0154036] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Accepted: 04/07/2016] [Indexed: 11/19/2022] Open
Abstract
1,3-1,4-β-glucanase is an important biocatalyst in brewing industry and animal feed industry, while its low thermostability often reduces its application performance. In this study, the thermostability of a mesophilic β-glucanase from Bacillus terquilensis was enhanced by rational design and engineering of disulfide bonds in the protein structure. Protein spatial configuration was analyzed to pre-exclude the residues pairs which negatively conflicted with the protein structure and ensure the contact of catalytic center. The changes in protein overall and local flexibility among the wild-type enzyme and the designated mutants were predicted to select the potential disulfide bonds for enhancement of thermostability. Two residue pairs (N31C-T187C and P102C-N125C) were chosen as engineering targets and both of them were proved to significantly enhance the protein thermostability. After combinational mutagenesis, the double mutant N31C-T187C/P102C-N125C showed a 48.3% increase in half-life value at 60°C and a 4.1°C rise in melting temperature (Tm) compared to wild-type enzyme. The catalytic property of N31C-T187C/P102C-N125C mutant was similar to that of wild-type enzyme. Interestingly, the optimal pH of double mutant was shifted from pH6.5 to pH6.0, which could also increase its industrial application. By comparison with mutants with single-Cys substitutions, the introduction of disulfide bonds and the induced new hydrogen bonds were proved to result in both local and overall rigidification and should be responsible for the improved thermostability. Therefore, the introduction of disulfide bonds for thermostability improvement could be rationally and highly-effectively designed by combination with spatial configuration analysis and molecular dynamics simulation.
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Affiliation(s)
- Chengtuo Niu
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of biotechnology, Jiangnan University, Wuxi, China
| | - Linjiang Zhu
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of biotechnology, Jiangnan University, Wuxi, China
| | - Xin Xu
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of biotechnology, Jiangnan University, Wuxi, China
| | - Qi Li
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of biotechnology, Jiangnan University, Wuxi, China
- State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, China
- * E-mail:
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Liu Z, Xie T, Zhong Q, Wang G. Crystal structure of CotA laccase complexed with 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonate) at a novel binding site. Acta Crystallogr F Struct Biol Commun 2016; 72:328-35. [PMID: 27050268 PMCID: PMC4822991 DOI: 10.1107/s2053230x1600426x] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2015] [Accepted: 03/13/2016] [Indexed: 01/13/2023] Open
Abstract
The CotA laccase from Bacillus subtilis is an abundant component of the spore outer coat and has been characterized as a typical laccase. The crystal structure of CotA complexed with 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) in a hole motif has been solved. The novel binding site was about 26 Å away from the T1 binding pocket. Comparison with known structures of other laccases revealed that the hole is a specific feature of CotA. The key residues Arg476 and Ser360 were directly bound to ABTS. Site-directed mutagenesis studies revealed that the residues Arg146, Arg429 and Arg476, which are located at the bottom of the novel binding site, are essential for the oxidation of ABTS and syringaldazine. Specially, a Thr480Phe variant was identified to be almost 3.5 times more specific for ABTS than for syringaldazine compared with the wild type. These results suggest this novel binding site for ABTS could be a potential target for protein engineering of CotA laccases.
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Affiliation(s)
- Zhongchuan Liu
- Key Laboratory of Environmental and Applied Microbiology, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, People’s Republic of China
- Key Laboratory of Environmental Microbiology of Sichuan Province, Chengdu 610041, People’s Republic of China
| | - Tian Xie
- Key Laboratory of Environmental and Applied Microbiology, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, People’s Republic of China
- Key Laboratory of Environmental Microbiology of Sichuan Province, Chengdu 610041, People’s Republic of China
| | - Qiuping Zhong
- Key Laboratory of Environmental and Applied Microbiology, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, People’s Republic of China
- Key Laboratory of Environmental Microbiology of Sichuan Province, Chengdu 610041, People’s Republic of China
- University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
| | - Ganggang Wang
- Key Laboratory of Environmental and Applied Microbiology, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, People’s Republic of China
- Key Laboratory of Environmental Microbiology of Sichuan Province, Chengdu 610041, People’s Republic of China
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Structural insight into the oxidation of sinapic acid by CotA laccase. J Struct Biol 2015; 190:155-61. [DOI: 10.1016/j.jsb.2015.03.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2014] [Revised: 03/09/2015] [Accepted: 03/09/2015] [Indexed: 01/22/2023]
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Martins LO, Durão P, Brissos V, Lindley PF. Laccases of prokaryotic origin: enzymes at the interface of protein science and protein technology. Cell Mol Life Sci 2015; 72:911-22. [PMID: 25572294 PMCID: PMC11113980 DOI: 10.1007/s00018-014-1822-x] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2014] [Accepted: 12/30/2014] [Indexed: 10/24/2022]
Abstract
The ubiquitous members of the multicopper oxidase family of enzymes oxidize a range of aromatic substrates such as polyphenols, methoxy-substituted phenols, amines and inorganic compounds, concomitantly with the reduction of molecular dioxygen to water. This family of enzymes can be broadly divided into two functional classes: metalloxidases and laccases. Several prokaryotic metalloxidases have been described in the last decade showing a robust activity towards metals, such as Cu(I), Fe(II) or Mn(II) and have been implicated in the metal metabolism of the corresponding microorganisms. Many laccases, with a superior efficiency for oxidation of organic compounds when compared with metals, have also been identified and characterized from prokaryotes, playing roles that more closely conform to those of intermediary metabolism. This review aims to present an update of current knowledge on prokaryotic multicopper oxidases, with a special emphasis on laccases, anticipating their enormous potential for industrial and environmental applications.
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Affiliation(s)
- Lígia O Martins
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, 2781-901, Oeiras, Portugal,
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Okano H, Ozaki M, Kanaya E, Kim JJ, Angkawidjaja C, Koga Y, Kanaya S. Structure and stability of metagenome-derived glycoside hydrolase family 12 cellulase (LC-CelA) a homolog of Cel12A from Rhodothermus marinus. FEBS Open Bio 2014; 4:936-46. [PMID: 25426413 PMCID: PMC4239480 DOI: 10.1016/j.fob.2014.10.013] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2014] [Revised: 10/27/2014] [Accepted: 10/27/2014] [Indexed: 11/24/2022] Open
Abstract
Ten novel cellulases, LC-CelA–J, were isolated from leaf–branch compost by a metagenomic approach. LC-CelA was characterized. The structure, activity, and stability of LC-CelA were similar to those of Cel12A from Rhodothermus marinus. Glu34-mediated hydrogen bonds and two disulfide bonds contribute to the stabilization of LC-CelA.
Ten genes encoding novel cellulases with putative signal peptides at the N-terminus, termed pre-LC-CelA–J, were isolated from a fosmid library of a leaf–branch compost metagenome by functional screening using agar plates containing carboxymethyl cellulose and trypan blue. All the cellulases except pre-LC-CelG have a 14–29 residue long flexible linker (FL) between the signal peptide and the catalytic domain. LC-CelA without a signal peptide (residues 20–261), which shows 76% amino acid sequence identity to Cel12A from Rhodothermus marinus (RmCel12A), was overproduced in Escherichiacoli, purified and characterized. LC-CelA exhibited its highest activity across a broad pH range (pH 5–9) and at 90 °C, indicating that LC-CelA is a highly thermostable cellulase, like RmCel12A. The crystal structure of LC-CelA was determined at 1.85 Å resolution and is nearly identical to that of RmCel12A determined in a form without the FL. Both proteins contain two disulfide bonds. LC-CelA has a 16-residue FL (residues 20–35), most of which is not visible in the electron density map, probably due to structural disorder. However, Glu34 and Pro35 form hydrogen bonds with the central region of the protein. ΔFL-LC-CelA (residues 36–261) and E34A-LC-CelA with a single Glu34 → Ala mutation were therefore constructed and characterized. ΔFL-LC-CelA and E34A-LC-CelA had lower melting temperatures (Tm) than LC-CelA by 14.7 and 12.0 °C respectively. The Tm of LC-CelA was also decreased by 28.0 °C in the presence of dithiothreitol. These results suggest that Glu34-mediated hydrogen bonds and the two disulfide bonds contribute to the stabilization of LC-CelA.
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Affiliation(s)
- Hiroyuki Okano
- Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Masashi Ozaki
- Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Eiko Kanaya
- Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Joong-Jae Kim
- Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Clement Angkawidjaja
- Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan ; International College, Osaka University, 1-30 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Yuichi Koga
- Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Shigenori Kanaya
- Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
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Liu Y, Cusano AM, Wallace EC, Mekmouche Y, Ullah S, Robert V, Tron T. Characterization of C-terminally engineered laccases. Int J Biol Macromol 2014; 69:435-41. [DOI: 10.1016/j.ijbiomac.2014.05.053] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2014] [Revised: 05/16/2014] [Accepted: 05/20/2014] [Indexed: 10/25/2022]
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Brander S, Mikkelsen JD, Kepp KP. Characterization of an alkali- and halide-resistant laccase expressed in E. coli: CotA from Bacillus clausii. PLoS One 2014; 9:e99402. [PMID: 24915287 PMCID: PMC4051777 DOI: 10.1371/journal.pone.0099402] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Accepted: 05/13/2014] [Indexed: 01/25/2023] Open
Abstract
The limitations of fungal laccases at higher pH and salt concentrations have intensified the search for new extremophilic bacterial laccases. We report the cloning, expression, and characterization of the bacterial cotA from Bacillus clausii, a supposed alkalophilic ortholog of cotA from B. subtilis. Both laccases were expressed in E. coli strain BL21(DE3) and characterized fully in parallel for strict benchmarking. We report activity on ABTS, SGZ, DMP, caffeic acid, promazine, phenyl hydrazine, tannic acid, and bilirubin at variable pH. Whereas ABTS, promazine, and phenyl hydrazine activities vs. pH were similar, the activity of B. clausii cotA was shifted upwards by ∼0.5–2 pH units for the simple phenolic substrates DMP, SGZ, and caffeic acid. This shift is not due to substrate affinity (KM) but to pH dependence of catalytic turnover: The kcat of B. clausii cotA was 1 s−1 at pH 6 and 5 s−1 at pH 8 in contrast to 6 s−1 at pH 6 and 2 s−1 at pH 8 for of B. subtilis cotA. Overall, kcat/KM was 10-fold higher for B. subtilis cotA at pHopt. While both proteins were heat activated, activation increased with pH and was larger in cotA from B. clausii. NaCl inhibited activity at acidic pH, but not up to 500–700 mM NaCl in alkaline pH, a further advantage of the alkali regime in laccase applications. The B. clausii cotA had ∼20 minutes half-life at 80°C, less than the ∼50 minutes at 80°C for cotA from B. subtilis. While cotA from B. subtilis had optimal stability at pH∼8, the cotA from B. clausii displayed higher combined salt- and alkali-resistance. This resistance is possibly caused by two substitutions (S427Q and V110E) that could repel anions to reduce anion-copper interactions at the expense of catalytic proficiency, a trade-off of potential relevance to laccase optimization.
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Affiliation(s)
- Søren Brander
- Technical University of Denmark, DTU Chemical Engineering, Kongens Lyngby, Denmark
- Technical University of Denmark, DTU Chemistry, Kongens Lyngby, Denmark
| | - Jørn D. Mikkelsen
- Technical University of Denmark, DTU Chemical Engineering, Kongens Lyngby, Denmark
| | - Kasper P. Kepp
- Technical University of Denmark, DTU Chemistry, Kongens Lyngby, Denmark
- * E-mail:
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12
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Sulaiman S, You DJ, Kanaya E, Koga Y, Kanaya S. Crystal structure and thermodynamic and kinetic stability of metagenome-derived LC-cutinase. Biochemistry 2014; 53:1858-69. [PMID: 24593046 DOI: 10.1021/bi401561p] [Citation(s) in RCA: 110] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The crystal structure of metagenome-derived LC-cutinase with polyethylene terephthalate (PET)-degrading activity was determined at 1.5 Å resolution. The structure strongly resembles that of Thermobifida alba cutinase. Ser165, Asp210, and His242 form the catalytic triad. Thermal denaturation and guanidine hydrochloride (GdnHCl)-induced unfolding of LC-cutinase were analyzed at pH 8.0 by circular dichroism spectroscopy. The midpoint of the transition of the thermal denaturation curve, T1/2, and that of the GdnHCl-induced unfolding curve, Cm, at 30 °C were 86.2 °C and 4.02 M, respectively. The free energy change of unfolding in the absence of GdnHCl, ΔG(H2O), was 41.8 kJ mol(-1) at 30 °C. LC-cutinase unfolded very slowly in GdnHCl with an unfolding rate, ku(H2O), of 3.28 × 10(-6) s(-1) at 50 °C. These results indicate that LC-cutinase is a kinetically robust protein. Nevertheless, the optimal temperature for the activity of LC-cutinase toward p-nitrophenyl butyrate (50 °C) was considerably lower than the T1/2 value. It increased by 10 °C in the presence of 1% polyethylene glycol (PEG) 1000. It also increased by at least 20 °C when PET was used as a substrate. These results suggest that the active site is protected from a heat-induced local conformational change by binding of PEG or PET. LC-cutinase contains one disulfide bond between Cys275 and Cys292. To examine whether this disulfide bond contributes to the thermodynamic and kinetic stability of LC-cutinase, C275/292A-cutinase without this disulfide bond was constructed. Thermal denaturation studies and equilibrium and kinetic studies of the GdnHCl-induced unfolding of C275/292A-cutinase indicate that this disulfide bond contributes not only to the thermodynamic stability but also to the kinetic stability of LC-cutinase.
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Affiliation(s)
- Sintawee Sulaiman
- Department of Material and Life Science, Graduate School of Engineering, Osaka University , 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
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13
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Unfolding pathway of CotA-laccase and the role of copper on the prevention of refolding through aggregation of the unfolded state. Biochem Biophys Res Commun 2012; 422:442-6. [DOI: 10.1016/j.bbrc.2012.05.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2012] [Accepted: 05/02/2012] [Indexed: 11/29/2022]
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