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Enhancing the catalytic activity of a novel GH5 cellulase GtCel5 from Gloeophyllum trabeum CBS 900.73 by site-directed mutagenesis on loop 6
BACKGROUND: Cellulases of glycosyl hydrolase (GH) family 5 share a (β/α)(8) TIM-barrel fold structure with eight βα loops surrounding the catalytic pocket. These loops exposed on the surface play a vital role in protein functions, primarily due to the interactions of some key amino acids with solven...
Autores principales: | , , , , , , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
BioMed Central
2018
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5863444/ https://www.ncbi.nlm.nih.gov/pubmed/29588661 http://dx.doi.org/10.1186/s13068-018-1080-5 |
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author | Zheng, Fei Tu, Tao Wang, Xiaoyu Wang, Yuan Ma, Rui Su, Xiaoyun Xie, Xiangming Yao, Bin Luo, Huiying |
author_facet | Zheng, Fei Tu, Tao Wang, Xiaoyu Wang, Yuan Ma, Rui Su, Xiaoyun Xie, Xiangming Yao, Bin Luo, Huiying |
author_sort | Zheng, Fei |
collection | PubMed |
description | BACKGROUND: Cellulases of glycosyl hydrolase (GH) family 5 share a (β/α)(8) TIM-barrel fold structure with eight βα loops surrounding the catalytic pocket. These loops exposed on the surface play a vital role in protein functions, primarily due to the interactions of some key amino acids with solvent and ligand molecules. It has been reported that motions of these loops facilitate substrate access and product release, and loops 6 and 7 located at the substrate entrance of the binding pocket promote proton transfer reaction at the catalytic site motions. However, the role of these flexible loops in catalysis of GH5 cellulase remains to be explored. RESULTS: In the present study, an acidic, mesophilic GH5 cellulase (with optimal activity at pH 4.0 and 70 °C), GtCel5, was identified in Gloeophyllum trabeum CBS 900.73. The specific activities of GtCel5 toward CMC-Na, barley β-glucan, and lichenan were 1117 ± 43, 6257 ± 26 and 5318 ± 54 U/mg, respectively. Multiple sequence alignment indicates that one amino acid residue at position 233 on the loop 6 shows semi-conservativeness and might contribute to the great catalytic performance. Saturation mutagenesis at position 233 was then conducted to reveal the vital roles of this position in enzyme properties. In comparison to the wild type, variants N233A and N233G showed decreased optimal temperature (− 10 °C) but increased activities (27 and 70%) and catalytic efficiencies (k(cat)/K(m); 45 and 52%), respectively. The similar roles of position 233 in catalytic performance were also verified in the other two GH5 homologs, TeEgl5A and PoCel5, by reverse mutation. Further molecular dynamics simulations suggested that the substitution of asparagine with alanine or glycine may introduce more hydrogen bonds, increase the flexibility of loop 6, enhance the interactions between enzyme and substrate, and thus improve the substrate affinity and catalytic efficiency. CONCLUSION: This study proposed a novel cellulase with potentials for industrial application. A specific position was identified to play key roles in cellulase–substrate interactions and enzyme catalysis. It is of great importance for understanding the binding mechanism of GH5 cellulases, and provides an effective strategy to improve the catalytic performance of cellulases. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13068-018-1080-5) contains supplementary material, which is available to authorized users. |
format | Online Article Text |
id | pubmed-5863444 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2018 |
publisher | BioMed Central |
record_format | MEDLINE/PubMed |
spelling | pubmed-58634442018-03-27 Enhancing the catalytic activity of a novel GH5 cellulase GtCel5 from Gloeophyllum trabeum CBS 900.73 by site-directed mutagenesis on loop 6 Zheng, Fei Tu, Tao Wang, Xiaoyu Wang, Yuan Ma, Rui Su, Xiaoyun Xie, Xiangming Yao, Bin Luo, Huiying Biotechnol Biofuels Research BACKGROUND: Cellulases of glycosyl hydrolase (GH) family 5 share a (β/α)(8) TIM-barrel fold structure with eight βα loops surrounding the catalytic pocket. These loops exposed on the surface play a vital role in protein functions, primarily due to the interactions of some key amino acids with solvent and ligand molecules. It has been reported that motions of these loops facilitate substrate access and product release, and loops 6 and 7 located at the substrate entrance of the binding pocket promote proton transfer reaction at the catalytic site motions. However, the role of these flexible loops in catalysis of GH5 cellulase remains to be explored. RESULTS: In the present study, an acidic, mesophilic GH5 cellulase (with optimal activity at pH 4.0 and 70 °C), GtCel5, was identified in Gloeophyllum trabeum CBS 900.73. The specific activities of GtCel5 toward CMC-Na, barley β-glucan, and lichenan were 1117 ± 43, 6257 ± 26 and 5318 ± 54 U/mg, respectively. Multiple sequence alignment indicates that one amino acid residue at position 233 on the loop 6 shows semi-conservativeness and might contribute to the great catalytic performance. Saturation mutagenesis at position 233 was then conducted to reveal the vital roles of this position in enzyme properties. In comparison to the wild type, variants N233A and N233G showed decreased optimal temperature (− 10 °C) but increased activities (27 and 70%) and catalytic efficiencies (k(cat)/K(m); 45 and 52%), respectively. The similar roles of position 233 in catalytic performance were also verified in the other two GH5 homologs, TeEgl5A and PoCel5, by reverse mutation. Further molecular dynamics simulations suggested that the substitution of asparagine with alanine or glycine may introduce more hydrogen bonds, increase the flexibility of loop 6, enhance the interactions between enzyme and substrate, and thus improve the substrate affinity and catalytic efficiency. CONCLUSION: This study proposed a novel cellulase with potentials for industrial application. A specific position was identified to play key roles in cellulase–substrate interactions and enzyme catalysis. It is of great importance for understanding the binding mechanism of GH5 cellulases, and provides an effective strategy to improve the catalytic performance of cellulases. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13068-018-1080-5) contains supplementary material, which is available to authorized users. BioMed Central 2018-03-22 /pmc/articles/PMC5863444/ /pubmed/29588661 http://dx.doi.org/10.1186/s13068-018-1080-5 Text en © The Author(s) 2018 Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. |
spellingShingle | Research Zheng, Fei Tu, Tao Wang, Xiaoyu Wang, Yuan Ma, Rui Su, Xiaoyun Xie, Xiangming Yao, Bin Luo, Huiying Enhancing the catalytic activity of a novel GH5 cellulase GtCel5 from Gloeophyllum trabeum CBS 900.73 by site-directed mutagenesis on loop 6 |
title | Enhancing the catalytic activity of a novel GH5 cellulase GtCel5 from Gloeophyllum trabeum CBS 900.73 by site-directed mutagenesis on loop 6 |
title_full | Enhancing the catalytic activity of a novel GH5 cellulase GtCel5 from Gloeophyllum trabeum CBS 900.73 by site-directed mutagenesis on loop 6 |
title_fullStr | Enhancing the catalytic activity of a novel GH5 cellulase GtCel5 from Gloeophyllum trabeum CBS 900.73 by site-directed mutagenesis on loop 6 |
title_full_unstemmed | Enhancing the catalytic activity of a novel GH5 cellulase GtCel5 from Gloeophyllum trabeum CBS 900.73 by site-directed mutagenesis on loop 6 |
title_short | Enhancing the catalytic activity of a novel GH5 cellulase GtCel5 from Gloeophyllum trabeum CBS 900.73 by site-directed mutagenesis on loop 6 |
title_sort | enhancing the catalytic activity of a novel gh5 cellulase gtcel5 from gloeophyllum trabeum cbs 900.73 by site-directed mutagenesis on loop 6 |
topic | Research |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5863444/ https://www.ncbi.nlm.nih.gov/pubmed/29588661 http://dx.doi.org/10.1186/s13068-018-1080-5 |
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