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Sulaeva I, Sto Pamo FG, Melikhov I, Budischowsky D, Rahikainen JL, Borisova A, Marjamaa K, Kruus K, Eijsink VGH, Várnai A, Potthast A. Beyond the Surface: A Methodological Exploration of Enzyme Impact along the Cellulose Fiber Cross-Section. Biomacromolecules 2024. [PMID: 38634234 DOI: 10.1021/acs.biomac.4c00152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/19/2024]
Abstract
Despite the wide range of analytical tools available for the characterization of cellulose, the in-depth characterization of inhomogeneous, layered cellulose fiber structures remains a challenge. When treating fibers or spinning man-made fibers, the question always arises as to whether the changes in the fiber structure affect only the surface or the entire fiber. Here, we developed an analysis tool based on the sequential limited dissolution of cellulose fiber layers. The method can reveal potential differences in fiber properties along the cross-sectional profile of natural or man-made cellulose fibers. In this analytical approach, carbonyl groups are labeled with a carbonyl selective fluorescence label (CCOA), after which thin fiber layers are sequentially dissolved with the solvent system DMAc/LiCl (9% w/v) and analyzed with size exclusion chromatography coupled with light scattering and fluorescence detection. The analysis of these fractions allowed for the recording of the changes in the chemical structure across the layers, resulting in a detailed cross-sectional profile of the different functionalities and molecular weight distributions. The method was optimized and tested in practice with LPMO (lytic polysaccharide monooxygenase)-treated cotton fibers, where it revealed the depth of fiber modification by the enzyme.
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Affiliation(s)
- Irina Sulaeva
- Core Facility Analysis of Lignocellulosics (ALICE), University of Natural Resources and Life Sciences, Vienna (BOKU), Konrad Lorenz-Strasse 24, A-3430 Tulln an der Donau, Austria
| | - Fredrik Gjerstad Sto Pamo
- Faculty of Chemistry, Biotechnology and Food Science, NMBU - Norwegian University of Life Sciences, 1432 Ås, Norway
| | - Ivan Melikhov
- Institute of Chemistry of Renewable Resources, Department of Chemistry, University of Natural Resources and Life Sciences, Vienna (BOKU), Konrad Lorenz-Strasse 24, A-3430 Tulln an der Donau, Austria
| | - David Budischowsky
- Institute of Chemistry of Renewable Resources, Department of Chemistry, University of Natural Resources and Life Sciences, Vienna (BOKU), Konrad Lorenz-Strasse 24, A-3430 Tulln an der Donau, Austria
| | - Jenni L Rahikainen
- Solutions for Natural Resources and Environment, VTT Technical Research Centre of Finland Ltd., Tietotie 2, FI-02044 Espoo, Finland
| | - Anna Borisova
- Solutions for Natural Resources and Environment, VTT Technical Research Centre of Finland Ltd., Tietotie 2, FI-02044 Espoo, Finland
| | - Kaisa Marjamaa
- Solutions for Natural Resources and Environment, VTT Technical Research Centre of Finland Ltd., Tietotie 2, FI-02044 Espoo, Finland
| | - Kristiina Kruus
- Solutions for Natural Resources and Environment, VTT Technical Research Centre of Finland Ltd., Tietotie 2, FI-02044 Espoo, Finland
- School of Chemical Engineering, Aalto University, P.O. Box 16100, 00076 Espoo, Finland
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, NMBU - Norwegian University of Life Sciences, 1432 Ås, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, NMBU - Norwegian University of Life Sciences, 1432 Ås, Norway
| | - Antje Potthast
- Institute of Chemistry of Renewable Resources, Department of Chemistry, University of Natural Resources and Life Sciences, Vienna (BOKU), Konrad Lorenz-Strasse 24, A-3430 Tulln an der Donau, Austria
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Støpamo FG, Sulaeva I, Budischowsky D, Rahikainen J, Marjamaa K, Potthast A, Kruus K, Eijsink VGH, Várnai A. Oxidation of cellulose fibers using LPMOs with varying allomorphic substrate preferences, oxidative regioselectivities, and domain structures. Carbohydr Polym 2024; 330:121816. [PMID: 38368098 DOI: 10.1016/j.carbpol.2024.121816] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2023] [Revised: 01/09/2024] [Accepted: 01/10/2024] [Indexed: 02/19/2024]
Abstract
Lytic polysaccharide monooxygenases (LPMOs) are excellent candidates for enzymatic functionalization of natural polysaccharides, such as cellulose or chitin, and are gaining relevance in the search for renewable biomaterials. Here, we assessed the cellulose fiber modification potential and catalytic performance of eleven cellulose-active fungal AA9-type LPMOs, including C1-, C4-, and C1/C4-oxidizing LPMOs with and without CBM1 carbohydrate-binding modules, on cellulosic substrates with different degrees of crystallinity and polymer chain arrangement, namely, Cellulose I, Cellulose II, and amorphous cellulose. The potential of LPMOs for cellulose fiber modification varied among the LPMOs and depended primarily on operational stability and substrate binding, and, to some extent, also on regioselectivity and domain structure. While all tested LPMOs were active on natural Cellulose I-type fibers, activity on the Cellulose II allomorph was almost exclusively detected for LPMOs containing a CBM1 and LPMOs with activity on soluble hemicelluloses and cello-oligosaccharides, for example NcAA9C from Neurospora crassa. The single-domain variant of NcAA9C oxidized the cellulose fibers to a higher extent than its CBM-containing natural variant and released less soluble products, indicating a more dispersed oxidation pattern without a CBM. Our findings reveal great functional variation among cellulose-active LPMOs, laying the groundwork for further LPMO-based cellulose engineering.
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Affiliation(s)
| | - Irina Sulaeva
- University of Natural Resources and Life Sciences (BOKU), Vienna, Austria.
| | - David Budischowsky
- University of Natural Resources and Life Sciences (BOKU), Vienna, Austria.
| | | | - Kaisa Marjamaa
- VTT Technical Research Centre of Finland, Espoo, Finland.
| | - Antje Potthast
- University of Natural Resources and Life Sciences (BOKU), Vienna, Austria.
| | - Kristiina Kruus
- VTT Technical Research Centre of Finland, Espoo, Finland; Aalto University, Espoo, Finland.
| | | | - Anikó Várnai
- Norwegian University of Life Sciences (NMBU), Ås, Norway.
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Sulaeva I, Budischowsky D, Rahikainen J, Marjamaa K, Støpamo FG, Khaliliyan H, Melikhov I, Rosenau T, Kruus K, Várnai A, Eijsink VGH, Potthast A. A novel approach to analyze the impact of lytic polysaccharide monooxygenases (LPMOs) on cellulosic fibres. Carbohydr Polym 2024; 328:121696. [PMID: 38220335 DOI: 10.1016/j.carbpol.2023.121696] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Revised: 11/26/2023] [Accepted: 12/12/2023] [Indexed: 01/16/2024]
Abstract
Enzymatic treatment of cellulosic fibres is a green alternative to classical chemical modification. For many applications, mild procedures for cellulose alteration are sufficient, in which the fibre structure and, therefore, the mechanical performance of cellulosic fibres are preserved. Lytic polysaccharide monooxygenases (LPMOs) bear a great potential to become a green reagent for such targeted cellulose modifications. An obstacle for wide implementation of LPMOs in tailored cellulose chemistry is the lack of suitable techniques to precisely monitor the LPMO impact on the polymer. Soluble oxidized cello-oligomers can be quantified using chromatographic and mass-spectrometric techniques. A considerable portion of the oxidized sites, however, remain on the insoluble cellulose fibres, and their quantification is difficult. Here, we describe a method for the simultaneous quantification of oxidized sites on cellulose fibres and changes in their molar mass distribution after treatment with LPMOs. The method is based on quantitative, heterogeneous, carbonyl-selective labelling with a fluorescent label (CCOA) followed by cellulose dissolution and size-exclusion chromatography (SEC). Application of the method to reactions of seven different LPMOs with pure cellulose fibres revealed pronounced functional differences between the enzymes, showing that this CCOA/SEC/MALS method is a promising tool to better understand the catalytic action of LPMOs.
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Affiliation(s)
- Irina Sulaeva
- Core Facility "Analysis of Lignocellulosics" (ALICE), University of Natural Resources and Life Sciences, Vienna (BOKU), Konrad Lorenz-Straße 24, A-3430 Tulln an der Donau, Austria
| | - David Budischowsky
- Institute of Chemistry of Renewable Resources, Department of Chemistry, University of Natural Resources and Life Sciences, Vienna (BOKU), Konrad Lorenz-Straße 24, A-3430 Tulln an der Donau, Austria
| | - Jenni Rahikainen
- Solutions for Natural Resources and Environment, VTT Technical Research Centre of Finland Ltd, Tietotie 2, FI-02044 Espoo, Finland
| | - Kaisa Marjamaa
- Solutions for Natural Resources and Environment, VTT Technical Research Centre of Finland Ltd, Tietotie 2, FI-02044 Espoo, Finland
| | - Fredrik Gjerstad Støpamo
- Faculty of Chemistry, Biotechnology and Food Science, NMBU - Norwegian University of Life Sciences, 1432 Ås, Norway
| | - Hajar Khaliliyan
- Institute of Chemistry of Renewable Resources, Department of Chemistry, University of Natural Resources and Life Sciences, Vienna (BOKU), Konrad Lorenz-Straße 24, A-3430 Tulln an der Donau, Austria
| | - Ivan Melikhov
- Institute of Chemistry of Renewable Resources, Department of Chemistry, University of Natural Resources and Life Sciences, Vienna (BOKU), Konrad Lorenz-Straße 24, A-3430 Tulln an der Donau, Austria
| | - Thomas Rosenau
- Institute of Chemistry of Renewable Resources, Department of Chemistry, University of Natural Resources and Life Sciences, Vienna (BOKU), Konrad Lorenz-Straße 24, A-3430 Tulln an der Donau, Austria
| | - Kristiina Kruus
- Solutions for Natural Resources and Environment, VTT Technical Research Centre of Finland Ltd, Tietotie 2, FI-02044 Espoo, Finland; School of Chemical Engineering, Aalto University, P.O. Box 16100, Espoo 00076 AALTO, Finland
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, NMBU - Norwegian University of Life Sciences, 1432 Ås, Norway
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, NMBU - Norwegian University of Life Sciences, 1432 Ås, Norway
| | - Antje Potthast
- Institute of Chemistry of Renewable Resources, Department of Chemistry, University of Natural Resources and Life Sciences, Vienna (BOKU), Konrad Lorenz-Straße 24, A-3430 Tulln an der Donau, Austria.
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Angeltveit CF, Várnai A, Eijsink VGH, Horn SJ. Enhancing enzymatic saccharification yields of cellulose at high solid loadings by combining different LPMO activities. Biotechnol Biofuels Bioprod 2024; 17:39. [PMID: 38461298 PMCID: PMC10924376 DOI: 10.1186/s13068-024-02485-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2024] [Accepted: 02/24/2024] [Indexed: 03/11/2024]
Abstract
BACKGROUND The polysaccharides in lignocellulosic biomass hold potential for production of biofuels and biochemicals. However, achieving efficient conversion of this resource into fermentable sugars faces challenges, especially when operating at industrially relevant high solid loadings. While it is clear that combining classical hydrolytic enzymes and lytic polysaccharide monooxygenases (LPMOs) is necessary to achieve high saccharification yields, exactly how these enzymes synergize at high solid loadings remains unclear. RESULTS An LPMO-poor cellulase cocktail, Celluclast 1.5 L, was spiked with one or both of two fungal LPMOs from Thermothielavioides terrestris and Thermoascus aurantiacus, TtAA9E and TaAA9A, respectively, to assess their impact on cellulose saccharification efficiency at high dry matter loading, using Avicel and steam-exploded wheat straw as substrates. The results demonstrate that LPMOs can mitigate the reduction in saccharification efficiency associated with high dry matter contents. The positive effect of LPMO inclusion depends on the type of feedstock and the type of LPMO and increases with the increasing dry matter content and reaction time. Furthermore, our results show that chelating free copper, which may leak out of the active site of inactivated LPMOs during saccharification, with EDTA prevents side reactions with in situ generated H2O2 and the reductant (ascorbic acid). CONCLUSIONS This study shows that sustaining LPMO activity is vital for efficient cellulose solubilization at high substrate loadings. LPMO cleavage of cellulose at high dry matter loadings results in new chain ends and thus increased water accessibility leading to decrystallization of the substrate, all factors making the substrate more accessible to cellulase action. Additionally, this work highlights the importance of preventing LPMO inactivation and its potential detrimental impact on all enzymes in the reaction.
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Affiliation(s)
- Camilla F Angeltveit
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Svein J Horn
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway.
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Østby H, Christensen IA, Hennum K, Várnai A, Buchinger E, Grandal S, Courtade G, Hegnar OA, Aachmann FL, Eijsink VGH. Functional characterization of a lytic polysaccharide monooxygenase from Schizophyllum commune that degrades non-crystalline substrates. Sci Rep 2023; 13:17373. [PMID: 37833388 PMCID: PMC10575960 DOI: 10.1038/s41598-023-44278-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2023] [Accepted: 10/05/2023] [Indexed: 10/15/2023] Open
Abstract
Lytic polysaccharide monooxygenases (LPMOs) are mono-copper enzymes that use O2 or H2O2 to oxidatively cleave glycosidic bonds. LPMOs are prevalent in nature, and the functional variation among these enzymes is a topic of great interest. We present the functional characterization of one of the 22 putative AA9-type LPMOs from the fungus Schizophyllum commune, ScLPMO9A. The enzyme, expressed in Escherichia coli, showed C4-oxidative cleavage of amorphous cellulose and soluble cello-oligosaccharides. Activity on xyloglucan, mixed-linkage β-glucan, and glucomannan was also observed, and product profiles differed compared to the well-studied C4-oxidizing NcLPMO9C from Neurospora crassa. While NcLPMO9C is also active on more crystalline forms of cellulose, ScLPMO9A is not. Differences between the two enzymes were also revealed by nuclear magnetic resonance (NMR) titration studies showing that, in contrast to NcLPMO9C, ScLPMO9A has higher affinity for linear substrates compared to branched substrates. Studies of H2O2-fueled degradation of amorphous cellulose showed that ScLPMO9A catalyzes a fast and specific peroxygenase reaction that is at least two orders of magnitude faster than the apparent monooxygenase reaction. Together, these results show that ScLPMO9A is an efficient LPMO with a broad substrate range, which, rather than acting on cellulose, has evolved to act on amorphous and soluble glucans.
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Affiliation(s)
- Heidi Østby
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Ås, Norway
| | - Idd A Christensen
- Norwegian Biopolymer Laboratory (NOBIPOL), Department of Biotechnology and Food Science, NTNU Norwegian University of Science and Technology, Sem Sælands Vei 6/8, 7491, Trondheim, Norway
| | - Karen Hennum
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Ås, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Ås, Norway
| | - Edith Buchinger
- Norwegian Biopolymer Laboratory (NOBIPOL), Department of Biotechnology and Food Science, NTNU Norwegian University of Science and Technology, Sem Sælands Vei 6/8, 7491, Trondheim, Norway
| | - Siri Grandal
- Norwegian Biopolymer Laboratory (NOBIPOL), Department of Biotechnology and Food Science, NTNU Norwegian University of Science and Technology, Sem Sælands Vei 6/8, 7491, Trondheim, Norway
| | - Gaston Courtade
- Norwegian Biopolymer Laboratory (NOBIPOL), Department of Biotechnology and Food Science, NTNU Norwegian University of Science and Technology, Sem Sælands Vei 6/8, 7491, Trondheim, Norway
| | - Olav A Hegnar
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Ås, Norway
| | - Finn L Aachmann
- Norwegian Biopolymer Laboratory (NOBIPOL), Department of Biotechnology and Food Science, NTNU Norwegian University of Science and Technology, Sem Sælands Vei 6/8, 7491, Trondheim, Norway
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Ås, Norway.
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Tuveng TR, Østby H, Tamburrini KC, Bissaro B, Hegnar OA, Stepnov AA, Várnai A, Berrin JG, Eijsink VGH. Revisiting the AA14 family of lytic polysaccharide monooxygenases and their catalytic activity. FEBS Lett 2023; 597:2086-2102. [PMID: 37418595 DOI: 10.1002/1873-3468.14694] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 06/08/2023] [Accepted: 06/26/2023] [Indexed: 07/09/2023]
Abstract
Lytic polysaccharide monooxygenases (LPMOs) belonging to the AA14 family are believed to contribute to the enzymatic degradation of lignocellulosic biomass by specifically acting on xylan in recalcitrant cellulose-xylan complexes. Functional characterization of an AA14 LPMO from Trichoderma reesei, TrAA14A, and a re-evaluation of the properties of the previously described AA14 from Pycnoporus coccineus, PcoAA14A, showed that these proteins have oxidase and peroxidase activities that are common for LPMOs. However, we were not able to detect activity on cellulose-associated xylan or any other tested polysaccharide substrate, meaning that the substrate of these enzymes remains unknown. Next to raising questions regarding the true nature of AA14 LPMOs, the present data illustrate possible pitfalls in the functional characterization of these intriguing enzymes.
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Affiliation(s)
- Tina R Tuveng
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Heidi Østby
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Ketty C Tamburrini
- INRAE, Aix Marseille Univ, UMR1163 Biodiversité et Biotechnologie Fongiques, Marseille, France
| | - Bastien Bissaro
- INRAE, Aix Marseille Univ, UMR1163 Biodiversité et Biotechnologie Fongiques, Marseille, France
| | - Olav A Hegnar
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Anton A Stepnov
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Jean-Guy Berrin
- INRAE, Aix Marseille Univ, UMR1163 Biodiversité et Biotechnologie Fongiques, Marseille, France
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
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Østby H, Várnai A. Hemicellulolytic enzymes in lignocellulose processing. Essays Biochem 2023; 67:533-550. [PMID: 37068264 PMCID: PMC10160854 DOI: 10.1042/ebc20220154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Revised: 01/25/2023] [Accepted: 01/30/2023] [Indexed: 04/19/2023]
Abstract
Lignocellulosic biomass is the most abundant source of carbon-based material on a global basis, serving as a raw material for cellulosic fibers, hemicellulosic polymers, platform sugars, and lignin resins or monomers. In nature, the various components of lignocellulose (primarily cellulose, hemicellulose, and lignin) are decomposed by saprophytic fungi and bacteria utilizing specialized enzymes. Enzymes are specific catalysts and can, in many cases, be produced on-site at lignocellulose biorefineries. In addition to reducing the use of often less environmentally friendly chemical processes, the application of such enzymes in lignocellulose processing to obtain a range of specialty products can maximize the use of the feedstock and valorize many of the traditionally underutilized components of lignocellulose, while increasing the economic viability of the biorefinery. While cellulose has a rich history of use in the pulp and paper industries, the hemicellulosic fraction of lignocellulose remains relatively underutilized in modern biorefineries, among other reasons due to the heterogeneous chemical structure of hemicellulose polysaccharides, the composition of which varies significantly according to the feedstock and the choice of pretreatment method and extraction solvent. This paper reviews the potential of hemicellulose in lignocellulose processing with focus on what can be achieved using enzymatic means. In particular, we discuss the various enzyme activities required for complete depolymerization of the primary hemicellulose types found in plant cell walls and for the upgrading of hemicellulosic polymers, oligosaccharides, and pentose sugars derived from hemicellulose depolymerization into a broad spectrum of value-added products.
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Affiliation(s)
- Heidi Østby
- Norwegian University of Life Sciences (NMBU), Faculty of Chemistry, Biotechnology and Food Science, P.O. Box 5003, N-1432 Aas, Norway
| | - Anikó Várnai
- Norwegian University of Life Sciences (NMBU), Faculty of Chemistry, Biotechnology and Food Science, P.O. Box 5003, N-1432 Aas, Norway
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Hansen LD, Eijsink VGH, Horn SJ, Várnai A. H 2 O 2 feeding enables LPMO-assisted cellulose saccharification during simultaneous fermentative production of lactic acid. Biotechnol Bioeng 2023; 120:726-736. [PMID: 36471631 DOI: 10.1002/bit.28298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Revised: 10/20/2022] [Accepted: 12/01/2022] [Indexed: 12/12/2022]
Abstract
Simultaneous saccharification and fermentation (SSF) is a well-known strategy for valorization of lignocellulosic biomass. Because the fermentation process typically is anaerobic, oxidative enzymes found in modern commercial cellulase cocktails, such as lytic polysaccharide monooxygenases (LPMOs), may be inhibited, limiting the overall efficiency of the enzymatic saccharification. Recent discoveries, however, have shown that LPMOs are active under anoxic conditions if they are provided with H2 O2 at low concentrations. In this study, we build on this concept and investigate the potential of using externally added H2 O2 to sustain oxidative cellulose depolymerization by LPMOs during an SSF process for lactic acid production. The results of bioreactor experiments with 100 g/L cellulose clearly show that continuous addition of small amounts of H2 O2 (at a rate of 80 µM/h) during SSF enables LPMO activity and improves lactic acid production. While further process optimization is needed, the present proof-of-concept results show that modern LPMO-containing cellulase cocktails such as Cellic CTec2 can be used in SSF setups, without sacrificing the LPMO activity in these cocktails.
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Affiliation(s)
- Line D Hansen
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Aas, Norway
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Aas, Norway
| | - Svein J Horn
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Aas, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Aas, Norway
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Chaudhari YB, Várnai A, Sørlie M, Horn SJ, Eijsink VGH. Engineering cellulases for conversion of lignocellulosic biomass. Protein Eng Des Sel 2023; 36:gzad002. [PMID: 36892404 PMCID: PMC10394125 DOI: 10.1093/protein/gzad002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2022] [Revised: 02/13/2023] [Accepted: 02/24/2023] [Indexed: 03/10/2023] Open
Abstract
Lignocellulosic biomass is a renewable source of energy, chemicals and materials. Many applications of this resource require the depolymerization of one or more of its polymeric constituents. Efficient enzymatic depolymerization of cellulose to glucose by cellulases and accessory enzymes such as lytic polysaccharide monooxygenases is a prerequisite for economically viable exploitation of this biomass. Microbes produce a remarkably diverse range of cellulases, which consist of glycoside hydrolase (GH) catalytic domains and, although not in all cases, substrate-binding carbohydrate-binding modules (CBMs). As enzymes are a considerable cost factor, there is great interest in finding or engineering improved and robust cellulases, with higher activity and stability, easy expression, and minimal product inhibition. This review addresses relevant engineering targets for cellulases, discusses a few notable cellulase engineering studies of the past decades and provides an overview of recent work in the field.
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Affiliation(s)
- Yogesh B Chaudhari
- Faculty of Chemistry, Biotechnology, and Food Science, NMBU-Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology, and Food Science, NMBU-Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway
| | - Morten Sørlie
- Faculty of Chemistry, Biotechnology, and Food Science, NMBU-Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway
| | - Svein J Horn
- Faculty of Chemistry, Biotechnology, and Food Science, NMBU-Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology, and Food Science, NMBU-Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway
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10
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van Eerde A, Várnai A, Wang Y, Paruch L, Jameson JK, Qiao F, Eiken HG, Su H, Eijsink VGH, Clarke JL. Successful Production and Ligninolytic Activity of a Bacterial Laccase, Lac51, Made in Nicotiana benthamiana via Transient Expression. Front Plant Sci 2022; 13:912293. [PMID: 35646038 PMCID: PMC9141054 DOI: 10.3389/fpls.2022.912293] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Accepted: 04/27/2022] [Indexed: 06/15/2023]
Abstract
Giant panda could have bamboo as their exclusive diet for about 2 million years because of the contribution of numerous enzymes produced by their gut bacteria, for instance laccases. Laccases are blue multi-copper oxidases that catalyze the oxidation of a broad spectrum of phenolic and aromatic compounds with water as the only byproduct. As a "green enzyme," laccases have potential in industrial applications, for example, when dealing with degradation of recalcitrant biopolymers, such as lignin. In the current study, a bacterial laccase, Lac51, originating from Pseudomonas putida and identified in the gut microbiome of the giant panda's gut was transiently expressed in the non-food plant Nicotiana benthamiana and characterized. Our results show that recombinant Lac51 exhibits bacterial laccase properties, with optimal pH and temperature at 7-8 and 40°C, respectively, when using syringaldazine as substrate. Moreover, we demonstrate the functional capability of the plant expressed Lac51 to oxidize lignin using selected lignin monomers that serve as substrates of Lac51. In summary, our study demonstrates the potential of green and non-food plants as a viable enzyme production platform for bacterial laccases. This result enriches our understanding of plant-made enzymes, as, to our knowledge, Lac51 is the first functional recombinant laccase produced in plants.
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Affiliation(s)
- André van Eerde
- NIBIO - Norwegian Institute of Bioeconomy Research, Ås, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Yanliang Wang
- NIBIO - Norwegian Institute of Bioeconomy Research, Ås, Norway
| | - Lisa Paruch
- NIBIO - Norwegian Institute of Bioeconomy Research, Ås, Norway
| | - John-Kristian Jameson
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Fen Qiao
- Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Haidian, China
| | - Hans Geir Eiken
- NIBIO - Norwegian Institute of Bioeconomy Research, Ås, Norway
| | - Hang Su
- NIBIO - Norwegian Institute of Bioeconomy Research, Ås, Norway
| | - Vincent G. H. Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
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11
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Støpamo FG, Røhr ÅK, Mekasha S, Petrović DM, Várnai A, Eijsink VGH. Characterization of a lytic polysaccharide monooxygenase from Aspergillus fumigatus shows functional variation among family AA11 fungal LPMOs. J Biol Chem 2021; 297:101421. [PMID: 34798071 PMCID: PMC8668981 DOI: 10.1016/j.jbc.2021.101421] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Revised: 11/05/2021] [Accepted: 11/08/2021] [Indexed: 11/26/2022] Open
Abstract
The discovery of oxidative cleavage of recalcitrant polysaccharides by lytic polysaccharide monooxygenases (LPMOs) has affected the study and industrial application of enzymatic biomass processing. Despite being widespread in fungi, LPMOs belonging to the auxiliary activity (AA) family AA11 have been understudied. While these LPMOs are considered chitin active, some family members have little or no activity toward chitin, and the only available crystal structure of an AA11 LPMO lacks features found in bacterial chitin-active AA10 LPMOs. Here, we report structural and functional characteristics of a single-domain AA11 LPMO from Aspergillus fumigatus, AfAA11A. The crystal structure shows a substrate-binding surface with features resembling those of known chitin-active LPMOs. Indeed, despite the absence of a carbohydrate-binding module, AfAA11A has considerable affinity for α-chitin and, more so, β-chitin. AfAA11A is active toward both these chitin allomorphs and enhances chitin degradation by an endoacting chitinase, in particular for α-chitin. The catalytic activity of AfAA11A on chitin increases when supplying reactions with hydrogen peroxide, showing that, like LPMOs from other families, AfAA11A has peroxygenase activity. These results show that, in stark contrast to the previously characterized AfAA11B from the same organism, AfAA11A likely plays a role in fungal chitin turnover. Thus, members of the hitherto rather enigmatic family of AA11 LPMOs show considerable structural and functional differences and may have multiple roles in fungal physiology.
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Affiliation(s)
- Fredrik Gjerstad Støpamo
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Åsmund Kjendseth Røhr
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Sophanit Mekasha
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Dejan M Petrović
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway.
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12
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Kadić A, Várnai A, Eijsink VGH, Horn SJ, Lidén G. In situ measurements of oxidation-reduction potential and hydrogen peroxide concentration as tools for revealing LPMO inactivation during enzymatic saccharification of cellulose. Biotechnol Biofuels 2021; 14:46. [PMID: 33602308 PMCID: PMC7893893 DOI: 10.1186/s13068-021-01894-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/24/2020] [Accepted: 02/01/2021] [Indexed: 06/12/2023]
Abstract
BACKGROUND Biochemical conversion of lignocellulosic biomass to simple sugars at commercial scale is hampered by the high cost of saccharifying enzymes. Lytic polysaccharide monooxygenases (LPMOs) may hold the key to overcome economic barriers. Recent studies have shown that controlled activation of LPMOs by a continuous H2O2 supply can boost saccharification yields, while overdosing H2O2 may lead to enzyme inactivation and reduce overall sugar yields. While following LPMO action by ex situ analysis of LPMO products confirms enzyme inactivation, currently no preventive measures are available to intervene before complete inactivation. RESULTS Here, we carried out enzymatic saccharification of the model cellulose Avicel with an LPMO-containing enzyme preparation (Cellic CTec3) and H2O2 feed at 1 L bioreactor scale and followed the oxidation-reduction potential and H2O2 concentration in situ with corresponding electrode probes. The rate of oxidation of the reductant as well as the estimation of the amount of H2O2 consumed by LPMOs indicate that, in addition to oxidative depolymerization of cellulose, LPMOs consume H2O2 in a futile non-catalytic cycle, and that inactivation of LPMOs happens gradually and starts long before the accumulation of LPMO-generated oxidative products comes to a halt. CONCLUSION Our results indicate that, in this model system, the collapse of the LPMO-catalyzed reaction may be predicted by the rate of oxidation of the reductant, the accumulation of H2O2 in the reactor or, indirectly, by a clear increase in the oxidation-reduction potential. Being able to monitor the state of the LPMO activity in situ may help maximizing the benefit of LPMO action during saccharification. Overcoming enzyme inactivation could allow improving overall saccharification yields beyond the state of the art while lowering LPMO and, potentially, cellulase loads, both of which would have beneficial consequences on process economics.
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Affiliation(s)
- Adnan Kadić
- Department of Chemical Engineering, Lund University, P.O. Box 118, 221 00, Lund, Sweden
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, NO-1432, Ås, Norway
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, NO-1432, Ås, Norway
| | - Svein Jarle Horn
- Faculty of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, NO-1432, Ås, Norway.
| | - Gunnar Lidén
- Department of Chemical Engineering, Lund University, P.O. Box 118, 221 00, Lund, Sweden.
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13
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Calderaro F, Keser M, Akeroyd M, Bevers LE, Eijsink VGH, Várnai A, van den Berg MA. Characterization of an AA9 LPMO from Thielavia australiensis, TausLPMO9B, under industrially relevant lignocellulose saccharification conditions. Biotechnol Biofuels 2020; 13:195. [PMID: 33292403 PMCID: PMC7706046 DOI: 10.1186/s13068-020-01836-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Accepted: 11/19/2020] [Indexed: 05/02/2023]
Abstract
BACKGROUND The discovery of lytic polysaccharide monooxygenases (LPMO) has changed our perspective on enzymatic degradation of plant biomass. Through an oxidative mechanism, these enzymes are able to cleave and depolymerize various polysaccharides, acting not only on crystalline substrates such as chitin and cellulose, but also on other polysaccharides, such as xyloglucan, glucomannan and starch. Despite their widespread use, uncertainties related to substrate specificity and stereospecificity, the nature of the co-substrate, in-process stability, and the nature of the optimal reductant challenge their exploitation in biomass processing applications. RESULTS In this work, we studied the properties of a novel fungal LPMO from the thermophilic fungus Thielavia australiensis, TausLPMO9B. Heterologous expression of TausLPMO9B in Aspergillus niger yielded a glycosylated protein with a methylated N-terminal histidine showing LPMO activity. High sequence identity of the AA9 domain to that of MtLPMO9B (MYCTH_80312) from Myceliophthora thermophila (84%) indicated strictly C1-oxidizing activity on cellulose, which was confirmed experimentally by the analysis of products released from cellulose using HPAEC. The enzyme was stable and active at a pH ranging from 4 to 6, thus matching the conditions commonly used in industrial biomass processing, where a low pH (between 4 and 5) is used due to the pH-optima of commercial cellulases and a desire to limit microbial contamination. CONCLUSION While the oxidative cleavage of phosphoric acid swollen cellulose (PASC) by TausLPMO9B was boosted by the addition of H2O2 as a co-substrate, this effect was not observed during the saccharification of acid pretreated corn stover. This illustrates key differences between the lab-scale tests with artificial, lignin-free substrates and industrial settings with lignocellulosic biomass as substrate.
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Affiliation(s)
- F Calderaro
- DSM Biotechnology Center, PP 699-0310, Alexander Fleminglaan 1, 2613 AX, Delft, The Netherlands.
- Molecular Enzymology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands.
| | - M Keser
- DSM Biotechnology Center, PP 699-0310, Alexander Fleminglaan 1, 2613 AX, Delft, The Netherlands
| | - M Akeroyd
- DSM Biotechnology Center, PP 699-0310, Alexander Fleminglaan 1, 2613 AX, Delft, The Netherlands
| | - L E Bevers
- DSM Biotechnology Center, PP 699-0310, Alexander Fleminglaan 1, 2613 AX, Delft, The Netherlands
| | - V G H Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - A Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - M A van den Berg
- DSM Biotechnology Center, PP 699-0310, Alexander Fleminglaan 1, 2613 AX, Delft, The Netherlands
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14
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Arntzen MØ, Bengtsson O, Várnai A, Delogu F, Mathiesen G, Eijsink VGH. Quantitative comparison of the biomass-degrading enzyme repertoires of five filamentous fungi. Sci Rep 2020; 10:20267. [PMID: 33219291 PMCID: PMC7679414 DOI: 10.1038/s41598-020-75217-z] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Accepted: 10/07/2020] [Indexed: 12/26/2022] Open
Abstract
The efficiency of microorganisms to degrade lignified plants is of great importance in the Earth's carbon cycle, but also in industrial biorefinery processes, such as for biofuel production. Here, we present a large-scale proteomics approach to investigate and compare the enzymatic response of five filamentous fungi when grown on five very different substrates: grass (sugarcane bagasse), hardwood (birch), softwood (spruce), cellulose and glucose. The five fungi included the ascomycetes Aspergillus terreus, Trichoderma reesei, Myceliophthora thermophila, Neurospora crassa and the white-rot basidiomycete Phanerochaete chrysosporium, all expressing a diverse repertoire of enzymes. In this study, we present comparable quantitative protein abundance values across five species and five diverse substrates. The results allow for direct comparison of fungal adaptation to the different substrates, give indications as to the substrate specificity of individual carbohydrate-active enzymes (CAZymes), and reveal proteins of unknown function that are co-expressed with CAZymes. Based on the results, we present a quantitative comparison of 34 lytic polysaccharide monooxygenases (LPMOs), which are crucial enzymes in biomass deconstruction.
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Affiliation(s)
- Magnus Ø Arntzen
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Ås, Norway.
| | - Oskar Bengtsson
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Ås, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Ås, Norway
| | - Francesco Delogu
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Ås, Norway
| | - Geir Mathiesen
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Ås, Norway
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Ås, Norway
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15
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Gaber Y, Rashad B, Hussein R, Abdelgawad M, Ali NS, Dishisha T, Várnai A. Heterologous expression of lytic polysaccharide monooxygenases (LPMOs). Biotechnol Adv 2020; 43:107583. [DOI: 10.1016/j.biotechadv.2020.107583] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Revised: 06/19/2020] [Accepted: 06/20/2020] [Indexed: 12/20/2022]
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16
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Østby H, Hansen LD, Horn SJ, Eijsink VGH, Várnai A. Enzymatic processing of lignocellulosic biomass: principles, recent advances and perspectives. J Ind Microbiol Biotechnol 2020; 47:623-657. [PMID: 32840713 PMCID: PMC7658087 DOI: 10.1007/s10295-020-02301-8] [Citation(s) in RCA: 55] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2020] [Accepted: 07/30/2020] [Indexed: 02/06/2023]
Abstract
Efficient saccharification of lignocellulosic biomass requires concerted development of a pretreatment method, an enzyme cocktail and an enzymatic process, all of which are adapted to the feedstock. Recent years have shown great progress in most aspects of the overall process. In particular, increased insights into the contributions of a wide variety of cellulolytic and hemicellulolytic enzymes have improved the enzymatic processing step and brought down costs. Here, we review major pretreatment technologies and different enzyme process setups and present an in-depth discussion of the various enzyme types that are currently in use. We pay ample attention to the role of the recently discovered lytic polysaccharide monooxygenases (LPMOs), which have led to renewed interest in the role of redox enzyme systems in lignocellulose processing. Better understanding of the interplay between the various enzyme types, as they may occur in a commercial enzyme cocktail, is likely key to further process improvements.
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Affiliation(s)
- Heidi Østby
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Aas, Norway
| | - Line Degn Hansen
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Aas, Norway
| | - Svein J Horn
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Aas, Norway
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Aas, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432, Aas, Norway.
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17
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Kojima Y, Várnai A, Eijsink VGH, Yoshida M. The Role of Lytic Polysaccharide Monooxygenases in Wood Rotting Basidiomycetes. TRENDS GLYCOSCI GLYC 2020. [DOI: 10.4052/tigg.2020.7j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Yuka Kojima
- Institute of Global Innovation, Tokyo University of Agriculture and Technology
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences
| | - Vincent G. H. Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences
| | - Makoto Yoshida
- Department of Environmental and Natural Resource Science, Tokyo University of Agriculture and Technology
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18
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Affiliation(s)
- Yuka Kojima
- Institute of Global Innovation, Tokyo University of Agriculture and Technology
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences
| | - Vincent G. H. Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences
| | - Makoto Yoshida
- Department of Environmental and Natural Resource Science, Tokyo University of Agriculture and Technology
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19
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Monclaro AV, Petrović DM, Alves GSC, Costa MMC, Midorikawa GEO, Miller RNG, Filho EXF, Eijsink VGH, Várnai A. Characterization of two family AA9 LPMOs from Aspergillus tamarii with distinct activities on xyloglucan reveals structural differences linked to cleavage specificity. PLoS One 2020; 15:e0235642. [PMID: 32640001 PMCID: PMC7343150 DOI: 10.1371/journal.pone.0235642] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2020] [Accepted: 06/19/2020] [Indexed: 11/23/2022] Open
Abstract
Aspergillus tamarii grows abundantly in naturally composting waste fibers of the textile industry and has a great potential in biomass decomposition. Amongst the key (hemi)cellulose-active enzymes in the secretomes of biomass-degrading fungi are the lytic polysaccharide monooxygenases (LPMOs). By catalyzing oxidative cleavage of glycoside bonds, LPMOs promote the activity of other lignocellulose-degrading enzymes. Here, we analyzed the catalytic potential of two of the seven AA9-type LPMOs that were detected in recently published transcriptome data for A. tamarii, namely AtAA9A and AtAA9B. Analysis of products generated from cellulose revealed that AtAA9A is a C4-oxidizing enzyme, whereas AtAA9B yielded a mixture of C1- and C4-oxidized products. AtAA9A was also active on cellopentaose and cellohexaose. Both enzymes also cleaved the β-(1→4)-glucan backbone of tamarind xyloglucan, but with different cleavage patterns. AtAA9A cleaved the xyloglucan backbone only next to unsubstituted glucosyl units, whereas AtAA9B yielded product profiles indicating that it can cleave the xyloglucan backbone irrespective of substitutions. Building on these new results and on the expanding catalog of xyloglucan- and oligosaccharide-active AA9 LPMOs, we discuss possible structural properties that could underlie the observed functional differences. The results corroborate evidence that filamentous fungi have evolved AA9 LPMOs with distinct substrate specificities and regioselectivities, which likely have complementary functions during biomass degradation.
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Affiliation(s)
- Antonielle V. Monclaro
- Laboratory of Enzymology, University of Brasília, Campus Universitário Darcy Ribeiro, Brasília, Brazil
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Dejan M. Petrović
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Gabriel S. C. Alves
- Laboratory of Microbiology, University of Brasília, Campus Universitário Darcy Ribeiro, Brasília, Brazil
| | - Marcos M. C. Costa
- Brazilian Agricultural Research Corporation, Embrapa CENARGEN, Brasília, Brazil
| | - Glaucia E. O. Midorikawa
- Laboratory of Microbiology, University of Brasília, Campus Universitário Darcy Ribeiro, Brasília, Brazil
| | - Robert N. G. Miller
- Laboratory of Microbiology, University of Brasília, Campus Universitário Darcy Ribeiro, Brasília, Brazil
| | - Edivaldo X. F. Filho
- Laboratory of Enzymology, University of Brasília, Campus Universitário Darcy Ribeiro, Brasília, Brazil
| | - Vincent G. H. Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
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20
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van Eerde A, Várnai A, Jameson JK, Paruch L, Moen A, Anonsen JH, Chylenski P, Steen HS, Heldal I, Bock R, Eijsink VGH, Liu‐Clarke J. In-depth characterization of Trichoderma reesei cellobiohydrolase TrCel7A produced in Nicotiana benthamiana reveals limitations of cellulase production in plants by host-specific post-translational modifications. Plant Biotechnol J 2020; 18:631-643. [PMID: 31373133 PMCID: PMC7004914 DOI: 10.1111/pbi.13227] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Revised: 07/01/2019] [Accepted: 07/26/2019] [Indexed: 05/17/2023]
Abstract
Sustainable production of biofuels from lignocellulose feedstocks depends on cheap enzymes for degradation of such biomass. Plants offer a safe and cost-effective production platform for biopharmaceuticals, vaccines and industrial enzymes boosting biomass conversion to biofuels. Production of intact and functional protein is a prerequisite for large-scale protein production, and extensive host-specific post-translational modifications (PTMs) often affect the catalytic properties and stability of recombinant enzymes. Here we investigated the impact of plant PTMs on enzyme performance and stability of the major cellobiohydrolase TrCel7A from Trichoderma reesei, an industrially relevant enzyme. TrCel7A was produced in Nicotiana benthamiana using a vacuum-based transient expression technology, and this recombinant enzyme (TrCel7Arec ) was compared with the native fungal enzyme (TrCel7Anat ) in terms of PTMs and catalytic activity on commercial and industrial substrates. We show that the N-terminal glutamate of TrCel7Arec was correctly processed by N. benthamiana to a pyroglutamate, critical for protein structure, while the linker region of TrCel7Arec was vulnerable to proteolytic digestion during protein production due to the absence of O-mannosylation in the plant host as compared with the native protein. In general, the purified full-length TrCel7Arec had 25% lower catalytic activity than TrCel7Anat and impaired substrate-binding properties, which can be attributed to larger N-glycans and lack of O-glycans in TrCel7Arec . All in all, our study reveals that the glycosylation machinery of N. benthamiana needs tailoring to optimize the production of efficient cellulases.
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Affiliation(s)
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food ScienceNorwegian University of Life Sciences (NMBU)ÅsNorway
| | - John Kristian Jameson
- Faculty of Chemistry, Biotechnology and Food ScienceNorwegian University of Life Sciences (NMBU)ÅsNorway
| | - Lisa Paruch
- NIBIONorwegian Institute of Bioeconomy ResearchÅsNorway
| | - Anders Moen
- Department of BiosciencesFaculty of Mathematics and Natural SciencesUniversity of Oslo (UiO)OsloNorway
| | - Jan Haug Anonsen
- Department of BiosciencesFaculty of Mathematics and Natural SciencesUniversity of Oslo (UiO)OsloNorway
| | - Piotr Chylenski
- Faculty of Chemistry, Biotechnology and Food ScienceNorwegian University of Life Sciences (NMBU)ÅsNorway
| | | | - Inger Heldal
- NIBIONorwegian Institute of Bioeconomy ResearchÅsNorway
| | - Ralph Bock
- Max Planck Institute of Molecular Plant PhysiologyPotsdam‐GolmGermany
| | - Vincent G. H. Eijsink
- Faculty of Chemistry, Biotechnology and Food ScienceNorwegian University of Life Sciences (NMBU)ÅsNorway
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21
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Petrović DM, Várnai A, Dimarogona M, Mathiesen G, Sandgren M, Westereng B, Eijsink VGH. Comparison of three seemingly similar lytic polysaccharide monooxygenases from Neurospora crassa suggests different roles in plant biomass degradation. J Biol Chem 2019; 294:15068-15081. [PMID: 31431506 DOI: 10.1074/jbc.ra119.008196] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Revised: 08/02/2019] [Indexed: 11/06/2022] Open
Abstract
Many fungi produce multiple lytic polysaccharide monooxygenases (LPMOs) with seemingly similar functions, but the biological reason for this multiplicity remains unknown. To address this question, here we carried out comparative structural and functional characterizations of three cellulose-active C4-oxidizing family AA9 LPMOs from the fungus Neurospora crassa, NcLPMO9A (NCU02240), NcLPMO9C (NCU02916), and NcLPMO9D (NCU01050). We solved the three-dimensional structure of copper-bound NcLPMO9A at 1.6-Å resolution and found that NcLPMO9A and NcLPMO9C, containing a CBM1 carbohydrate-binding module, bind cellulose more strongly and were less susceptible to inactivation than NcLPMO9D, which lacks a CBM. All three LPMOs were active on tamarind xyloglucan and konjac glucomannan, generating similar products but clearly differing in activity levels. Importantly, in some cases, the addition of phosphoric acid-swollen cellulose (PASC) had a major effect on activity: NcLPMO9A was active on xyloglucan only in the presence of PASC, and PASC enhanced NcLPMO9D activity on glucomannan. Interestingly, the three enzymes also exhibited large differences in their interactions with enzymatic electron donors, which could reflect that they are optimized to act with different reducing partners. All three enzymes efficiently used H2O2 as a cosubstrate, yielding product profiles identical to those obtained in O2-driven reactions with PASC, xyloglucan, or glucomannan. Our results indicate that seemingly similar LPMOs act preferentially on different types of copolymeric substructures in the plant cell wall, possibly because these LPMOs are functionally adapted to distinct niches differing in the types of available reductants.
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Affiliation(s)
- Dejan M Petrović
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), 1432 Ås, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), 1432 Ås, Norway
| | - Maria Dimarogona
- Department of Molecular Sciences, Swedish University of Agricultural Sciences, 75007 Uppsala, Sweden.,Laboratory of Biotechnology and Structural Biology, Department of Chemical Engineering, University of Patras, 26504 Patras, Greece
| | - Geir Mathiesen
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), 1432 Ås, Norway
| | - Mats Sandgren
- Department of Molecular Sciences, Swedish University of Agricultural Sciences, 75007 Uppsala, Sweden
| | - Bjørge Westereng
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), 1432 Ås, Norway
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), 1432 Ås, Norway
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22
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Petrović DM, Bissaro B, Chylenski P, Skaugen M, Sørlie M, Jensen MS, Aachmann FL, Courtade G, Várnai A, Eijsink VGH. Methylation of the N-terminal histidine protects a lytic polysaccharide monooxygenase from auto-oxidative inactivation. Protein Sci 2019; 27:1636-1650. [PMID: 29971843 DOI: 10.1002/pro.3451] [Citation(s) in RCA: 79] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Revised: 06/01/2018] [Accepted: 06/04/2018] [Indexed: 12/29/2022]
Abstract
The catalytically crucial N-terminal histidine (His1) of fungal lytic polysaccharide monooxygenases (LPMOs) is post-translationally modified to carry a methylation. The functional role of this methylation remains unknown. We have carried out an in-depth functional comparison of two variants of a family AA9 LPMO from Thermoascus aurantiacus (TaLPMO9A), one with, and one without the methylation on His1. Various activity assays showed that the two enzyme variants are identical in terms of substrate preferences, cleavage specificities and the ability to activate molecular oxygen. During the course of this work, new functional features of TaLPMO9A were discovered, in particular the ability to cleave xyloglucan, and these features were identical for both variants. Using a variety of techniques, we further found that methylation has minimal effects on the pKa of His1, the affinity for copper and the redox potential of bound copper. The two LPMOs did, however, show clear differences in their resistance against oxidative damage. Studies with added hydrogen peroxide confirmed recent claims that low concentrations of H2 O2 boost LPMO activity, whereas excess H2 O2 leads to LPMO inactivation. The methylated variant of TaLPMO9A, produced in Aspergillus oryzae, was more resistant to excess H2 O2 and showed better process performance when using conditions that promote generation of reactive-oxygen species. LPMOs need to protect themselves from reactive oxygen species generated in their active sites and this study shows that methylation of the fully conserved N-terminal histidine provides such protection.
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Affiliation(s)
- Dejan M Petrović
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Bastien Bissaro
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Piotr Chylenski
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Morten Skaugen
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Morten Sørlie
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Marianne S Jensen
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Finn L Aachmann
- Department of Biotechnology and Food Science, NOBIPOL, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Gaston Courtade
- Department of Biotechnology and Food Science, NOBIPOL, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
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23
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Chylenski P, Bissaro B, Sørlie M, Røhr ÅK, Várnai A, Horn SJ, Eijsink VG. Lytic Polysaccharide Monooxygenases in Enzymatic Processing of Lignocellulosic Biomass. ACS Catal 2019. [DOI: 10.1021/acscatal.9b00246] [Citation(s) in RCA: 90] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Piotr Chylenski
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, N-1432 Ås, Norway
| | - Bastien Bissaro
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, N-1432 Ås, Norway
| | - Morten Sørlie
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, N-1432 Ås, Norway
| | - Åsmund K. Røhr
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, N-1432 Ås, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, N-1432 Ås, Norway
| | - Svein J. Horn
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, N-1432 Ås, Norway
| | - Vincent G.H. Eijsink
- Faculty of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, N-1432 Ås, Norway
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24
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Eijsink VGH, Petrovic D, Forsberg Z, Mekasha S, Røhr ÅK, Várnai A, Bissaro B, Vaaje-Kolstad G. On the functional characterization of lytic polysaccharide monooxygenases (LPMOs). Biotechnol Biofuels 2019; 12:58. [PMID: 30923566 PMCID: PMC6423801 DOI: 10.1186/s13068-019-1392-0] [Citation(s) in RCA: 88] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2019] [Accepted: 03/06/2019] [Indexed: 05/02/2023]
Abstract
Lytic polysaccharide monooxygenases (LPMOs) are abundant in nature and best known for their role in the enzymatic conversion of recalcitrant polysaccharides such as chitin and cellulose. LPMO activity requires an oxygen co-substrate, which was originally thought to be O2, but which may also be H2O2. Functional characterization of LPMOs is not straightforward because typical reaction mixtures will promote side reactions, including auto-catalytic inactivation of the enzyme. For example, despite some recent progress, there is still limited insight into the kinetics of the LPMO reaction. Recent discoveries concerning the role of H2O2 in LPMO catalysis further complicate the picture. Here, we review commonly used methods for characterizing LPMOs, with focus on benefits and potential pitfalls, rather than on technical details. We conclude by pointing at a few key problems and potential misconceptions that should be taken into account when interpreting existing data and planning future experiments.
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Affiliation(s)
- Vincent G. H. Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), PO Box 5003, 1432 Ås, Norway
| | - Dejan Petrovic
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), PO Box 5003, 1432 Ås, Norway
| | - Zarah Forsberg
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), PO Box 5003, 1432 Ås, Norway
| | - Sophanit Mekasha
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), PO Box 5003, 1432 Ås, Norway
| | - Åsmund K. Røhr
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), PO Box 5003, 1432 Ås, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), PO Box 5003, 1432 Ås, Norway
| | - Bastien Bissaro
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), PO Box 5003, 1432 Ås, Norway
| | - Gustav Vaaje-Kolstad
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), PO Box 5003, 1432 Ås, Norway
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25
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Takeda K, Umezawa K, Várnai A, Eijsink VG, Igarashi K, Yoshida M, Nakamura N. Fungal PQQ-dependent dehydrogenases and their potential in biocatalysis. Curr Opin Chem Biol 2018; 49:113-121. [PMID: 30580186 DOI: 10.1016/j.cbpa.2018.12.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Revised: 11/16/2018] [Accepted: 12/04/2018] [Indexed: 10/27/2022]
Abstract
In 2014, the first fungal pyrroloquinoline-quinone (PQQ)-dependent enzyme was discovered as a pyranose dehydrogenase from the basidiomycete Coprinopsis cinerea (CcPDH). This discovery laid the foundation for a new Auxiliary Activities (AA) family, AA12, in the Carbohydrate-Active enZymes (CAZy) database and revealed a novel enzymatic activity potentially involved in biomass conversion. This review summarizes recent progress made in research on this fungal oxidoreductase and related enzymes. CcPDH consists of the catalytic PQQ-binding AA12 domain, an N-terminal cytochrome b AA8 domain, and a C-terminal family 1 carbohydrate-binding module (CBM1). CcPDH oxidizes 2-keto-d-glucose (d-glucosone), l-fucose, and rare sugars such as d-arabinose and l-galactose, and can activate lytic polysaccharide monooxygenases (LPMOs). Bioinformatic studies suggest a widespread occurrence of quinoproteins in eukaryotes as well as prokaryotes.
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Affiliation(s)
- Kouta Takeda
- Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan
| | - Kiwamu Umezawa
- Department of Applied Biological Chemistry, Kindai University, Nara 631-8505, Japan
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), 1432 Ås, Norway
| | - Vincent Gh Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), 1432 Ås, Norway
| | - Kiyohiko Igarashi
- Department of Biomaterial Sciences, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Makoto Yoshida
- Department of Environmental and Natural Resource Science, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan.
| | - Nobuhumi Nakamura
- Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan
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Abstract
Biomass constitutes an appealing alternative to fossil resources for the production of materials and energy. The abundance and attractiveness of vegetal biomass come along with challenges pertaining to the intricacy of its structure, evolved during billions of years to face and resist abiotic and biotic attacks. To achieve the daunting goal of plant cell wall decomposition, microorganisms have developed many (enzymatic) strategies, from which we seek inspiration to develop biotechnological processes. A major breakthrough in the field has been the discovery of enzymes today known as lytic polysaccharide monooxygenases (LPMOs), which, by catalyzing the oxidative cleavage of recalcitrant polysaccharides, allow canonical hydrolytic enzymes to depolymerize the biomass more efficiently. Very recently, it has been shown that LPMOs are not classical monooxygenases in that they can also use hydrogen peroxide (H2O2) as an oxidant. This discovery calls for a revision of our understanding of how lignocellulolytic enzymes are connected since H2O2 is produced and used by several of them. The first part of this review is dedicated to the LPMO paradigm, describing knowns, unknowns, and uncertainties. We then present different lignocellulolytic redox systems, enzymatic or not, that depend on fluxes of reactive oxygen species (ROS). Based on an assessment of these putatively interconnected systems, we suggest that fine-tuning of H2O2 levels and proximity between sites of H2O2 production and consumption are important for fungal biomass conversion. In the last part of this review, we discuss how our evolving understanding of redox processes involved in biomass depolymerization may translate into industrial applications.
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Affiliation(s)
- Bastien Bissaro
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Aas, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Aas, Norway
| | - Åsmund K Røhr
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Aas, Norway
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Aas, Norway
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27
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Kadowaki MAS, Várnai A, Jameson JK, T. Leite AE, Costa-Filho AJ, Kumagai PS, Prade RA, Polikarpov I, Eijsink VGH. Functional characterization of a lytic polysaccharide monooxygenase from the thermophilic fungus Myceliophthora thermophila. PLoS One 2018; 13:e0202148. [PMID: 30125294 PMCID: PMC6101365 DOI: 10.1371/journal.pone.0202148] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2018] [Accepted: 07/27/2018] [Indexed: 12/29/2022] Open
Abstract
Thermophilic fungi are a promising source of thermostable enzymes able to hydrolytically or oxidatively degrade plant cell wall components. Among these enzymes are lytic polysaccharide monooxygenases (LPMOs), enzymes capable of enhancing biomass hydrolysis through an oxidative mechanism. Myceliophthora thermophila (synonym Sporotrichum thermophile), an Ascomycete fungus, expresses and secretes over a dozen different LPMOs. In this study, we report the overexpression and biochemical study of a previously uncharacterized LPMO (MtLPMO9J) from M. thermophila M77 in Aspergillus nidulans. MtLPMO9J is a single-domain LPMO and has 63% sequence similarity with the catalytic domain of NcLPMO9C from Neurospora crassa. Biochemical characterization of MtLPMO9J revealed that it performs C4-oxidation and is active against cellulose, soluble cello-oligosaccharides and xyloglucan. Moreover, biophysical studies showed that MtLPMO9J is structurally stable at pH above 5 and at temperatures up to 50°C. Importantly, LC-MS analysis of the peptides after tryptic digestion of the recombinantly produced protein revealed not only the correct processing of the signal peptide and methylation of the N-terminal histidine, but also partial autoxidation of the catalytic center. This shows that redox conditions need to be controlled, not only during LPMO reactions but also during protein production, to protect LPMOs from oxidative damage.
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Affiliation(s)
- Marco A. S. Kadowaki
- Department of Physics and Interdisciplinary Science, São Carlos Institute of Physics, University of São Paulo, São Carlos, São Paulo, Brazil
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - John-Kristian Jameson
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Ana E. T. Leite
- Department of Physics and Interdisciplinary Science, São Carlos Institute of Physics, University of São Paulo, São Carlos, São Paulo, Brazil
| | - Antonio J. Costa-Filho
- Department of Physics, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo, Brazil
| | - Patricia S. Kumagai
- Department of Physics and Interdisciplinary Science, São Carlos Institute of Physics, University of São Paulo, São Carlos, São Paulo, Brazil
| | - Rolf A. Prade
- Departments of Biochemistry & Molecular Biology and Microbiology & Molecular Genetics, Oklahoma State University, Stillwater, OK, United States
| | - Igor Polikarpov
- Department of Physics and Interdisciplinary Science, São Carlos Institute of Physics, University of São Paulo, São Carlos, São Paulo, Brazil
| | - Vincent G. H. Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
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28
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Várnai A, Umezawa K, Yoshida M, Eijsink VGH. The Pyrroloquinoline-Quinone-Dependent Pyranose Dehydrogenase from Coprinopsis cinerea Drives Lytic Polysaccharide Monooxygenase Action. Appl Environ Microbiol 2018; 84:e00156-18. [PMID: 29602785 PMCID: PMC5960967 DOI: 10.1128/aem.00156-18] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2018] [Accepted: 03/28/2018] [Indexed: 01/21/2023] Open
Abstract
Fungi secrete a set of glycoside hydrolases and oxidoreductases, including lytic polysaccharide monooxygenases (LPMOs), for the degradation of plant polysaccharides. LPMOs catalyze the oxidative cleavage of glycosidic bonds after activation by an external electron donor. So far, only flavin-dependent oxidoreductases (from the auxiliary activity [AA] family AA3) have been shown to activate LPMOs. Here, we present LPMO activation by a pyrroloquinoline-quinone (PQQ)-dependent pyranose dehydrogenase (PDH) from Coprinopsis cinerea, CcPDH, the founding member of the recently discovered auxiliary activity family AA12. CcPDH contains a C-terminal family 1 carbohydrate binding module (CBM1), an N-terminal family AA8 cytochrome domain, and a central AA12 dehydrogenase domain. We have studied the ability of full-length CcPDH and its truncated variants to drive catalysis by two Neurospora crassa LPMOs. The results show that CcPDH indeed can activate the C-1-oxidizing N. crassa LPMO 9F (NcLPMO9F) and the C-4-oxidizing Neurospora crassa LPMO 9C (NcLPMO9C), that this activation depends on the cytochrome domain, and that the dehydrogenase and the LPMO reactions are strongly coupled. The two tested CcPDH-LPMO systems showed quite different efficiencies, and this difference disappeared upon the addition of free PQQ acting as a diphenol/quinone redox mediator, showing that LPMOs differ when it comes to their direct interactions with the cytochrome domain. Surprisingly, removal of the CBM domain from CcPDH had a considerable negative impact on the efficiency of the CcPDH-LPMO systems, suggesting that electron transfer in the vicinity of the substrate is beneficial. CcPDH does not oxidize cello-oligosaccharides, which makes this enzyme a useful tool for studying cellulose-oxidizing LPMOs.IMPORTANCE Lytic polysaccharide monooxygenases (LPMOs) are currently receiving increasing attention because of their importance in degrading recalcitrant polysaccharides and their potential roles in biological processes, such as bacterial virulence. LPMO action requires an external electron donor, and fungi growing on biomass secrete various so-called glucose-methanol-choline (GMC) oxidoreductases, including cellobiose dehydrogenase, which can donate electrons to LPMOs. This paper describes how an enzyme not belonging to the GMC oxidoreductase family, CcPDH, can activate LPMOs, and it provides new insights into the activation process by (i) describing the roles of individual CcPDH domains (a dehydrogenase, a cytochrome, and a carbohydrate-binding domain), (ii) showing that the PDH and LPMO enzyme reactions are strongly coupled, (iii) demonstrating that LPMOs differ in terms of their efficiencies of activation by the same activator, and (iv) providing indications that electron transferring close to the substrate surface is beneficial for the overall efficiency of the CcPDH-LPMO system.
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Affiliation(s)
- Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Kiwamu Umezawa
- Department of Environmental and Natural Resource Science, Tokyo University of Agriculture and Technology, Tokyo, Japan
| | - Makoto Yoshida
- Department of Environmental and Natural Resource Science, Tokyo University of Agriculture and Technology, Tokyo, Japan
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
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29
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Arntzen MØ, Várnai A, Mackie RI, Eijsink VGH, Pope PB. Outer membrane vesicles from Fibrobacter succinogenes S85 contain an array of carbohydrate-active enzymes with versatile polysaccharide-degrading capacity. Environ Microbiol 2017; 19:2701-2714. [PMID: 28447389 DOI: 10.1111/1462-2920.13770] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2017] [Accepted: 04/18/2017] [Indexed: 11/30/2022]
Abstract
Fibrobacter succinogenes is an anaerobic bacterium naturally colonising the rumen and cecum of herbivores where it utilizes an enigmatic mechanism to deconstruct cellulose into cellobiose and glucose, which serve as carbon sources for growth. Here, we illustrate that outer membrane vesicles (OMVs) released by F. succinogenes are enriched with carbohydrate-active enzymes and that intact OMVs were able to depolymerize a broad range of linear and branched hemicelluloses and pectin, despite the inability of F. succinogenes to utilize non-cellulosic (pentose) sugars for growth. We hypothesize that the degradative versatility of F. succinogenes OMVs is used to prime hydrolysis by destabilising the tight networks of polysaccharides intertwining cellulose in the plant cell wall, thus increasing accessibility of the target substrate for the host cell. This is supported by observations that OMV-pretreatment of the natural complex substrate switchgrass increased the catalytic efficiency of a commercial cellulose-degrading enzyme cocktail by 2.4-fold. We also show that the OMVs contain a putative multiprotein complex, including the fibro-slime protein previously found to be important in binding to crystalline cellulose. We hypothesize that this complex has a function in plant cell wall degradation, either by catalysing polysaccharide degradation itself, or by targeting the vesicles to plant biomass.
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Affiliation(s)
- Magnus Ø Arntzen
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway
| | - Anikó Várnai
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway
| | - Roderick I Mackie
- Institute for Genomic Biology, and Department of Animal Sciences, University of Illinois at Urbana-Champaign, IL, USA
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway
| | - Phillip B Pope
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway
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30
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Chylenski P, Forsberg Z, Ståhlberg J, Várnai A, Lersch M, Bengtsson O, Sæbø S, Horn SJ, Eijsink VGH. Development of minimal enzyme cocktails for hydrolysis of sulfite-pulped lignocellulosic biomass. J Biotechnol 2017; 246:16-23. [PMID: 28219736 DOI: 10.1016/j.jbiotec.2017.02.009] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2016] [Revised: 01/26/2017] [Accepted: 02/13/2017] [Indexed: 01/02/2023]
Abstract
Despite recent progress, saccharification of lignocellulosic biomass is still a major cost driver in biorefining. In this study, we present the development of minimal enzyme cocktails for hydrolysis of Norway spruce and sugarcane bagasse, which were pretreated using the so-called BALI™ process, which is based on sulfite pulping technology. Minimal enzyme cocktails were composed using several glycoside hydrolases purified from the industrially relevant filamentous fungus Trichoderma reesei and a purified commercial β-glucosidase from Aspergillus niger. The contribution of in-house expressed lytic polysaccharide monooxygenases (LPMOs) was also tested, since oxidative cleavage of cellulose by such LPMOs is known to be beneficial for conversion efficiency. We show that the optimized cocktails permit efficient saccharification at reasonable enzyme loadings and that the effect of the LPMOs is substrate-dependent. Using a cocktail comprising only four enzymes, glucan conversion for Norway spruce reached >80% at enzyme loadings of 8mg/g glucan, whereas almost 100% conversion was achieved at 16mg/g.
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Affiliation(s)
- Piotr Chylenski
- Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Zarah Forsberg
- Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Jerry Ståhlberg
- Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences, Uppsala, Sweden
| | - Anikó Várnai
- Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | | | | | - Solve Sæbø
- Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Svein Jarle Horn
- Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Vincent G H Eijsink
- Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), Ås, Norway.
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31
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Nekiunaite L, Petrović DM, Westereng B, Vaaje-Kolstad G, Hachem MA, Várnai A, Eijsink VG. Fg
LPMO9A from Fusarium graminearum
cleaves xyloglucan independently of the backbone substitution pattern. FEBS Lett 2016; 590:3346-3356. [DOI: 10.1002/1873-3468.12385] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2016] [Revised: 08/11/2016] [Accepted: 08/22/2016] [Indexed: 01/08/2023]
Affiliation(s)
- Laura Nekiunaite
- Enzyme and Protein Chemistry; Department of Systems Biology; Technical University of Denmark; Kongens Lyngby Denmark
| | - Dejan M. Petrović
- Department of Chemistry, Biotechnology and Food Science; Norwegian University of Life Sciences; Aas Norway
| | - Bjørge Westereng
- Department of Chemistry, Biotechnology and Food Science; Norwegian University of Life Sciences; Aas Norway
| | - Gustav Vaaje-Kolstad
- Department of Chemistry, Biotechnology and Food Science; Norwegian University of Life Sciences; Aas Norway
| | - Maher Abou Hachem
- Enzyme and Protein Chemistry; Department of Systems Biology; Technical University of Denmark; Kongens Lyngby Denmark
| | - Anikó Várnai
- Department of Chemistry, Biotechnology and Food Science; Norwegian University of Life Sciences; Aas Norway
| | - Vincent G.H. Eijsink
- Department of Chemistry, Biotechnology and Food Science; Norwegian University of Life Sciences; Aas Norway
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32
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Borisova AS, Isaksen T, Dimarogona M, Kognole AA, Mathiesen G, Várnai A, Røhr ÅK, Payne CM, Sørlie M, Sandgren M, Eijsink VGH. Structural and Functional Characterization of a Lytic Polysaccharide Monooxygenase with Broad Substrate Specificity. J Biol Chem 2015; 290:22955-69. [PMID: 26178376 DOI: 10.1074/jbc.m115.660183] [Citation(s) in RCA: 139] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Indexed: 01/02/2023] Open
Abstract
The recently discovered lytic polysaccharide monooxygenases (LPMOs) carry out oxidative cleavage of polysaccharides and are of major importance for efficient processing of biomass. NcLPMO9C from Neurospora crassa acts both on cellulose and on non-cellulose β-glucans, including cellodextrins and xyloglucan. The crystal structure of the catalytic domain of NcLPMO9C revealed an extended, highly polar substrate-binding surface well suited to interact with a variety of sugar substrates. The ability of NcLPMO9C to act on soluble substrates was exploited to study enzyme-substrate interactions. EPR studies demonstrated that the Cu(2+) center environment is altered upon substrate binding, whereas isothermal titration calorimetry studies revealed binding affinities in the low micromolar range for polymeric substrates that are due in part to the presence of a carbohydrate-binding module (CBM1). Importantly, the novel structure of NcLPMO9C enabled a comparative study, revealing that the oxidative regioselectivity of LPMO9s (C1, C4, or both) correlates with distinct structural features of the copper coordination sphere. In strictly C1-oxidizing LPMO9s, access to the solvent-facing axial coordination position is restricted by a conserved tyrosine residue, whereas access to this same position seems unrestricted in C4-oxidizing LPMO9s. LPMO9s known to produce a mixture of C1- and C4-oxidized products show an intermediate situation.
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Affiliation(s)
- Anna S Borisova
- From the Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden
| | - Trine Isaksen
- the Department of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences, N-1432 Ås, Norway
| | - Maria Dimarogona
- From the Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden
| | - Abhishek A Kognole
- the Department of Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky 40506
| | - Geir Mathiesen
- the Department of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences, N-1432 Ås, Norway
| | - Anikó Várnai
- the Department of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences, N-1432 Ås, Norway
| | - Åsmund K Røhr
- the Department of Biosciences, University of Oslo, N-0316 Oslo, Norway, and
| | - Christina M Payne
- From the Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden, the Department of Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky 40506
| | - Morten Sørlie
- the Department of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences, N-1432 Ås, Norway
| | - Mats Sandgren
- From the Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden,
| | - Vincent G H Eijsink
- the Department of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences, N-1432 Ås, Norway,
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Müller G, Várnai A, Johansen KS, Eijsink VGH, Horn SJ. Harnessing the potential of LPMO-containing cellulase cocktails poses new demands on processing conditions. Biotechnol Biofuels 2015; 8:187. [PMID: 26609322 PMCID: PMC4659242 DOI: 10.1186/s13068-015-0376-y] [Citation(s) in RCA: 147] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Accepted: 11/09/2015] [Indexed: 05/02/2023]
Abstract
BACKGROUND The emerging bioeconomy depends on improved methods for processing of lignocellulosic biomass to fuels and chemicals. Saccharification of lignocellulose to fermentable sugars is a key step in this regard where enzymatic catalysis plays an important role and is a major cost driver. Traditionally, enzyme cocktails for the conversion of cellulose to fermentable sugars mainly consisted of hydrolytic cellulases. However, the recent discovery of lytic polysaccharide monooxygenases (LPMOs), which cleave cellulose using molecular oxygen and an electron donor, has provided new tools for biomass saccharification. RESULTS Current commercial enzyme cocktails contain LPMOs, which, considering the unique properties of these enzymes, may change optimal processing conditions. Here, we show that such modern cellulase cocktails release up to 60 % more glucose from a pretreated lignocellulosic substrate under aerobic conditions compared to anaerobic conditions. This higher yield correlates with the accumulation of oxidized products, which is a signature of LPMO activity. Spiking traditional cellulase cocktails with LPMOs led to increased saccharification yields, but only under aerobic conditions. LPMO activity on pure cellulose depended on the addition of an external electron donor, whereas this was not required for LPMO activity on lignocellulose. CONCLUSIONS In this study, we demonstrate a direct correlation between saccharification yield and LPMO activity of commercial enzyme cocktails. Importantly, we show that the LPMO contribution to overall efficiency may be large if process conditions are adapted to the key determinants of LPMO activity, namely the presence of electron donors and molecular oxygen. Thus, the advent of LPMOs has a great potential, but requires rethinking of industrial bioprocessing procedures.
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Affiliation(s)
- Gerdt Müller
- />Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, P. O. Box 5003, 1432 Ås, Norway
| | - Anikó Várnai
- />Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, P. O. Box 5003, 1432 Ås, Norway
| | - Katja Salomon Johansen
- />Biofuels Technology, Novozymes A/S, Krogshøjvej 36, 2880 Bagsværd, Denmark
- />Division of Industrial Biotechnology, Chalmers University of Technology, Kemivägen 10, 412 96 Gothenburg, Sweden
| | - Vincent G. H. Eijsink
- />Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, P. O. Box 5003, 1432 Ås, Norway
| | - Svein Jarle Horn
- />Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, P. O. Box 5003, 1432 Ås, Norway
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Várnai A, Tang C, Bengtsson O, Atterton A, Mathiesen G, Eijsink VGH. Expression of endoglucanases in Pichia pastoris under control of the GAP promoter. Microb Cell Fact 2014; 13:57. [PMID: 24742273 PMCID: PMC4021498 DOI: 10.1186/1475-2859-13-57] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2013] [Accepted: 04/14/2014] [Indexed: 12/15/2022] Open
Abstract
Background Plant-derived biomass is a potential alternative to fossil feedstocks for a greener economy. Enzymatic saccharification of biomass has been studied extensively and endoglucanases have been found to be a prerequisite for quick initial liquefaction of biomass under industrial conditions. Pichia pastoris, widely used for heterologous protein expression, can be utilized for fungal endoglucanase production. The recently marketed PichiaPink™ expression system allows for rapid clone selection, and employs the methanol inducible AOX1 promoter to ensure high protein expression levels. However, methanol is toxic and poses a fire hazard, issues which become more significant at an industrial scale. It is possible to eliminate these risks and still maintain high productivity by switching to the constitutive GAP promoter. Results In the present study, a plasmid carrying the constitutive GAP promoter was created for PichiaPink™. We then studied expression of two endoglucanases, AfCel12A from Aspergillus fumigatus and TaCel5A from Thermoascus aurantiacus, regulated by either the AOX1 promoter or the GAP promoter. Initial experiments in tubes and small bioreactors showed that the levels of AfCel12A obtained with the constitutive promoter were similar or higher, compared to the AOX1 promoter, whereas the levels of TaCel5A were somewhat lower. After optimization of cultivation conditions using a 15-l bioreactor, the recombinant P. pastoris strains utilizing the GAP promoter produced ca. 3–5 g/l of total secreted protein, with CMCase activity equivalent to 1200 nkat/ml AfCel12A and 170 nkat/ml TaCel5A. Conclusions We present a strategy for constitutive recombinant protein expression in the novel PichiaPink™ system. Both AfCel12A and TaCel5A were successfully expressed constitutively in P. pastoris under the GAP promoter. Reasonable protein levels were reached after optimizing cultivation conditions.
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Affiliation(s)
- Anikó Várnai
- Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, PO Box 5003Chr, Magnus Falsens vei 1, N-1432 Ås, Norway.
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Pakarinen A, Haven MØ, Djajadi DT, Várnai A, Puranen T, Viikari L. Cellulases without carbohydrate-binding modules in high consistency ethanol production process. Biotechnol Biofuels 2014; 7:27. [PMID: 24559384 PMCID: PMC3974600 DOI: 10.1186/1754-6834-7-27] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Accepted: 02/06/2014] [Indexed: 05/24/2023]
Abstract
BACKGROUND Enzymes still comprise a major part of ethanol production costs from lignocellulose raw materials. Irreversible binding of enzymes to the residual substrate prevents their reuse and no efficient methods for recycling of enzymes have so far been presented. Cellulases without a carbohydrate-binding module (CBM) have been found to act efficiently at high substrate consistencies and to remain non-bound after the hydrolysis. RESULTS High hydrolysis yields could be obtained with thermostable enzymes of Thermoascus aurantiacus containing only two main cellulases: cellobiohydrolase I (CBH I), Cel7A and endoglucanase II (EG II), Cel5A. The yields were decreased by only about 10% when using these cellulases without CBM. A major part of enzymes lacking CBM was non-bound during the most active stage of hydrolysis and in spite of this, produced high sugar yields. Complementation of the two cellulases lacking CBM with CBH II (CtCel6A) improved the hydrolysis. Cellulases without CBM were more sensitive during exposure to high ethanol concentration than the enzymes containing CBM. Enzymes lacking CBM could be efficiently reused leading to a sugar yield of 90% of that with fresh enzymes. The applicability of cellulases without CBM was confirmed under industrial ethanol production conditions at high (25% dry matter (DM)) consistency. CONCLUSIONS The results clearly show that cellulases without CBM can be successfully used in the hydrolysis of lignocellulose at high consistency, and that this approach could provide new means for better recyclability of enzymes. This paper provides new insight into the efficient action of CBM-lacking cellulases. The relationship of binding and action of cellulases without CBM at high DM consistency should, however, be studied in more detail.
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Affiliation(s)
- Annukka Pakarinen
- Department of Food and Environmental Sciences, University of Helsinki, PO 27, 00014 Helsinki, Finland
| | | | - Demi Tristan Djajadi
- Department of Food and Environmental Sciences, University of Helsinki, PO 27, 00014 Helsinki, Finland
| | - Anikó Várnai
- Department of Food and Environmental Sciences, University of Helsinki, PO 27, 00014 Helsinki, Finland
- Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, PO Box 5003, N-1432 Aas, Norway
| | - Terhi Puranen
- Roal Oy, Tykkimäentie 15, FIN-05200 Rajamäki, Finland
| | - Liisa Viikari
- Department of Food and Environmental Sciences, University of Helsinki, PO 27, 00014 Helsinki, Finland
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Moilanen U, Kellock M, Várnai A, Andberg M, Viikari L. Mechanisms of laccase-mediator treatments improving the enzymatic hydrolysis of pre-treated spruce. Biotechnol Biofuels 2014; 7:177. [PMID: 25648942 PMCID: PMC4297466 DOI: 10.1186/s13068-014-0177-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Accepted: 12/03/2014] [Indexed: 05/02/2023]
Abstract
BACKGROUND The recalcitrance of softwood to enzymatic hydrolysis is one of the major bottlenecks hindering its profitable use as a raw material for platform sugars. In softwood, the guaiacyl-type lignin is especially problematic, since it is known to bind hydrolytic enzymes non-specifically, rendering them inactive towards cellulose. One approach to improve hydrolysis yields is the modification of lignin and of cellulose structures by laccase-mediator treatments (LMTs). RESULTS LMTs were studied to improve the hydrolysis of steam pre-treated spruce (SPS). Three mediators with three distinct reaction mechanisms (ABTS, HBT, and TEMPO) and one natural mediator (AS, that is, acetosyringone) were tested. Of the studied LMTs, laccase-ABTS treatment improved the degree of hydrolysis by 54%, while acetosyringone and TEMPO increased the hydrolysis yield by 49% and 36%, respectively. On the other hand, laccase-HBT treatment improved the degree of hydrolysis only by 22%, which was in the same order of magnitude as the increase induced by laccase treatment without added mediators (19%). The improvements were due to lignin modification that led to reduced adsorption of endoglucanase Cel5A and cellobiohydrolase Cel7A on lignin. TEMPO was the only mediator that modified cellulose structure by oxidizing hydroxyls at the C6 position to carbonyls and partially further to carboxyls. Oxidation of the reducing end C1 carbonyls was also observed. In contrast to lignin modification, oxidation of cellulose impaired enzymatic hydrolysis. CONCLUSIONS LMTs, in general, improved the enzymatic hydrolysis of SPS. The mechanism of the improvement was shown to be based on reduced adsorption of the main cellulases on SPS lignin rather than cellulose oxidation. In fact, at higher mediator concentrations the advantage of lignin modification in enzymatic saccharification was overcome by the negative effect of cellulose oxidation. For future applications, it would be beneficial to be able to understand and modify the binding properties of lignin in order to decrease unspecific enzyme binding and thus to increase the mobility, action, and recyclability of the hydrolytic enzymes.
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Affiliation(s)
- Ulla Moilanen
- />Department of Food and Environmental Sciences, University of Helsinki, PO Box 27, Helsinki, 00014 Finland
| | - Miriam Kellock
- />Department of Food and Environmental Sciences, University of Helsinki, PO Box 27, Helsinki, 00014 Finland
- />VTT Technical Research Centre of Finland, PO Box 1000, Espoo, 02044 Finland
| | - Anikó Várnai
- />Department of Food and Environmental Sciences, University of Helsinki, PO Box 27, Helsinki, 00014 Finland
- />Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, PO Box 5003, Aas, N-1432 Norway
| | - Martina Andberg
- />VTT Technical Research Centre of Finland, PO Box 1000, Espoo, 02044 Finland
| | - Liisa Viikari
- />Department of Food and Environmental Sciences, University of Helsinki, PO Box 27, Helsinki, 00014 Finland
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Várnai A, Costa THF, Faulds CB, Milagres AMF, Siika-aho M, Ferraz A. Effects of enzymatic removal of plant cell wall acylation (acetylation, p-coumaroylation, and feruloylation) on accessibility of cellulose and xylan in natural (non-pretreated) sugar cane fractions. Biotechnol Biofuels 2014; 7:153. [PMID: 25328538 PMCID: PMC4201721 DOI: 10.1186/s13068-014-0153-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Accepted: 09/30/2014] [Indexed: 05/05/2023]
Abstract
BACKGROUND Sugar cane internodes can be divided diagonally into four fractions, of which the two innermost ones are the least recalcitrant pith and the moderately accessible pith-rind interface. These fractions differ in enzymatic hydrolyzability due to structural differences. In general, cellulose hydrolysis in plants is hindered by its physical interaction with hemicellulose and lignin. Lignin is believed to be linked covalently to hemicellulose through hydroxycinnamic acids, forming a compact matrix around the polysaccharides. Acetyl xylan esterase and three feruloyl esterases were evaluated for their potential to fragment the lignocellulosic network in sugar cane and to indirectly increase the accessibility of cellulose. RESULTS The hydrolyzability of the pith and pith-rind interface fractions of a low-lignin-containing sugar cane clone (H58) was compared to that of a reference cultivar (RC). Acetyl xylan esterase enhanced the rate and overall yield of cellulose and xylan hydrolysis in all four substrates. Of the three feruloyl esterases tested, only TsFaeC was capable of releasing p-coumaric acid, while AnFaeA and NcFaeD released ferulic acid from both the pith and interface fractions. Ferulic acid release was higher from the less recalcitrant clone (H58)/fraction (pith), whereas more p-coumaric acid was released from the clone (RC)/fraction (interface) with a higher lignin content. In addition, a compositional analysis of the four fractions revealed that p-coumaroyl content correlated with lignin, while feruloyl content correlated with arabinose content, suggesting different esterification patterns of these two hydroxycinnamic acids. Despite the extensive release of phenolic acids, feruloyl esterases only moderately promoted enzyme access to cellulose or xylan. CONCLUSIONS Acetyl xylan esterase TrAXE was more efficient in enhancing the overall saccharification of sugar cane, compared to the feruloyl esterases AnFaeA, TsFaeC, and NcFaeD. The hydroxycinnamic acid composition of sugar cane fractions and the hydrolysis data together suggest that feruloyl groups are more likely to decorate xylan, while p-coumaroyl groups are rather linked to lignin. The three different feruloyl esterases had distinct product profiles on non-pretreated sugar cane substrate, indicating that sugar cane pith could function as a possible natural substrate for feruloyl esterase activity measurements. Hydrolysis data suggest that TsFaeC was able to release p-coumaroyl groups esterifying lignin.
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Affiliation(s)
- Anikó Várnai
- />Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, P.O. Box 5003, N-1432, Aas, Norway
- />VTT Technical Research Centre of Finland, P.O. Box 1000, Espoo, 02044 VTT Finland
- />Department of Food and Environmental Sciences, University of Helsinki, P.O. Box 27, Helsinki, 00014 Finland
| | - Thales HF Costa
- />Departamento de Biotecnologia, Escola de Engenharia de Lorena, Universidade de São Paulo, 12602-810 Lorena, SP Brasil
| | - Craig B Faulds
- />INRA, UMR 1163 Biodiversité et Biotechnologie Fongiques (BBF), POLYTECH, Aix Marseille Université, 163 avenue de Luminy, 13288 Marseille, Cedex 09 France
- />Aix-Marseille Université, INRA, BBF UMR_A 1163, 163 avenue de Luminy, 13288 Marseille, cedex 09 France
| | - Adriane MF Milagres
- />Departamento de Biotecnologia, Escola de Engenharia de Lorena, Universidade de São Paulo, 12602-810 Lorena, SP Brasil
| | - Matti Siika-aho
- />VTT Technical Research Centre of Finland, P.O. Box 1000, Espoo, 02044 VTT Finland
| | - André Ferraz
- />Departamento de Biotecnologia, Escola de Engenharia de Lorena, Universidade de São Paulo, 12602-810 Lorena, SP Brasil
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Le Costaouëc T, Pakarinen A, Várnai A, Puranen T, Viikari L. The role of carbohydrate binding module (CBM) at high substrate consistency: comparison of Trichoderma reesei and Thermoascus aurantiacus Cel7A (CBHI) and Cel5A (EGII). Bioresour Technol 2013; 143:196-203. [PMID: 23796604 DOI: 10.1016/j.biortech.2013.05.079] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2013] [Revised: 05/20/2013] [Accepted: 05/21/2013] [Indexed: 05/09/2023]
Abstract
The role of CBM in two fungal model cellulase systems, consisting of Cel7A and Cel5A, from Trichoderma reesei and Thermoascus aurantiacus, were compared in the hydrolysis of various substrates. For comparison, family-1 CBM's were introduced to the T. aurantiacus and removed from the T. reesei enzymes. Especially at high dry matter consistencies of lignocellulosic substrates, pretreated wheat straw and spruce, the T. aurantiacus enzymes lacking CBM outperformed the enzymes carrying the CBM. In these conditions, the CBM-less enzymes from both organisms obviously recognized and bound to the substrate at higher probability than in dilute systems. Avoiding the unproductive binding to lignin caused by the CBMs obviously enhanced the hydrolytic performance. The lignin binding effect was, however, not entirely caused by the CBM, but also by the different structures and affinities of the core enzymes to lignin. Due to decreased binding, the CBM-less enzymes would allow reuse, potentially decreasing hydrolysis costs.
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Affiliation(s)
- Tinaïg Le Costaouëc
- University of Helsinki, Food and Environmental Sciences, P.O. Box 27, 00014 Helsinki, Finland.
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Várnai A, Siika-aho M, Viikari L. Carbohydrate-binding modules (CBMs) revisited: reduced amount of water counterbalances the need for CBMs. Biotechnol Biofuels 2013; 6:30. [PMID: 23442543 PMCID: PMC3599012 DOI: 10.1186/1754-6834-6-30] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2012] [Accepted: 02/04/2013] [Indexed: 05/07/2023]
Abstract
BACKGROUND A vast number of organisms are known to produce structurally diversified cellulases capable of degrading cellulose, the most abundant biopolymer on earth. The generally accepted paradigm is that the carbohydrate-binding modules (CBMs) of cellulases are required for efficient saccharification of insoluble substrates. Based on sequence data, surprisingly more than 60% of the cellulases identified lack carbohydrate-binding modules or alternative protein structures linked to cellulases (dockerins). This finding poses the question about the role of the CBMs: why would most cellulases lack CBMs, if they are necessary for the efficient hydrolysis of cellulose? RESULTS The advantage of CBMs, which increase the affinity of cellulases to substrates, was found to be diminished by reducing the amount of water in the hydrolytic system, which increases the probability of enzyme-substrate interaction. At low substrate concentration (1% w/w), CBMs were found to be more important in the catalytic performance of the cellobiohydrolases TrCel7A and TrCel6A of Trichoderma reesei as compared to that of the endoglucanases TrCel5A and TrCel7B. Increasing the substrate concentration while maintaining the enzyme-to-substrate ratio enhanced adsorption of TrCel7A, independent of the presence of the CBM. At 20% (w/w) substrate concentration, the hydrolytic performance of cellulases without CBMs caught up with that of cellulases with CBMs. This phenomenon was more noticeable on the lignin-containing pretreated wheat straw as compared to the cellulosic Avicel, presumably due to unproductive adsorption of enzymes to lignin. CONCLUSIONS Here we propose that the water content in the natural environments of carbohydrate-degrading organisms might have led to the evolution of various substrate-binding structures. In addition, some well recognized problems of economical saccharification such as unproductive binding of cellulases, which reduces the hydrolysis rate and prevents recycling of enzymes, could be partially overcome by omitting CBMs. This finding could help solve bottlenecks of enzymatic hydrolysis of lignocelluloses and speed up commercialization of second generation bioethanol.
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Affiliation(s)
- Anikó Várnai
- Department of Food and Environmental Sciences, University of Helsinki, P.O. Box 27, 00014, Helsinki, Finland
| | - Matti Siika-aho
- VTT Technical Research Centre of Finland, P.O. Box 1000, 02044 VTT, Espoo, Finland
| | - Liisa Viikari
- Department of Food and Environmental Sciences, University of Helsinki, P.O. Box 27, 00014, Helsinki, Finland
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Penttilä PA, Várnai A, Pere J, Tammelin T, Salmén L, Siika-aho M, Viikari L, Serimaa R. Xylan as limiting factor in enzymatic hydrolysis of nanocellulose. Bioresour Technol 2013; 129:135-41. [PMID: 23238342 DOI: 10.1016/j.biortech.2012.11.017] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2012] [Revised: 11/01/2012] [Accepted: 11/02/2012] [Indexed: 05/10/2023]
Abstract
The role of xylan as a limiting factor in the enzymatic hydrolysis of cellulose was studied by hydrolysing nanocellulose samples prepared by mechanical fibrillation of birch pulp with varying xylan content. Analyzing the nanocelluloses and their hydrolysis residues with dynamic FT-IR spectroscopy revealed that a certain fraction of xylan remained tightly attached to cellulose fibrils despite partial hydrolysis of xylan with xylanase prior to pulp fibrillation and that this fraction remained in the structure during the hydrolysis of nanocellulose with cellulase mixture as well. Thus, a loosely bound fraction of xylan was predicted to have been more likely removed by purified xylanase. The presence of loosely bound xylan seemed to limit the hydrolysis of crystalline cellulose, indicated by an increase in cellulose crystallinity and by preserved crystal width measured with wide-angle X-ray scattering. Removing loosely bound xylan led to a proportional hydrolysis of xylan and cellulose with the cellulase mixture.
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Affiliation(s)
- Paavo A Penttilä
- University of Helsinki, Department of Physics, P.O. Box 64, FI-00014 Helsinki, Finland.
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Várnai A, Huikko L, Pere J, Siika-Aho M, Viikari L. Synergistic action of xylanase and mannanase improves the total hydrolysis of softwood. Bioresour Technol 2011; 102:9096-104. [PMID: 21757337 DOI: 10.1016/j.biortech.2011.06.059] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2011] [Revised: 06/10/2011] [Accepted: 06/14/2011] [Indexed: 05/02/2023]
Abstract
The impact of xylan and glucomannan hydrolysis on cellulose hydrolysis was studied on five pretreated softwood substrates with different xylan and glucomannan contents, both varying from 0.2% to 6.9%, using mixtures of purified enzymes. The supplementation of pure cellulase mixture with non-specific endoglucanase TrCel7B and xylanase TrXyn11 enhanced the hydrolysis of all substrates, except the steam pretreated spruce, by more than 50%. The addition of endo-β-mannanase increased the overall hydrolysis yield by 20-25%, liberating significantly more glucose than theoretically present in glucomannan. When supplemented together, xylanolytic and mannanolytic enzymes acted synergistically with cellulases. Moreover, a linear correlation was observed between the hydrolysis of polysaccharides, irrespective of the composition, indicating that glucomannan and xylan form a complex network of polysaccharides around the cellulosic fibres extending throughout the lignocellulosic matrix. Both hemicellulolytic enzymes are crucial as accessory enzymes when designing efficient mixtures for the total hydrolysis of lignocellulosic substrates containing both hemicelluloses.
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Affiliation(s)
- Anikó Várnai
- University of Helsinki, Food and Environmental Sciences, P.O. Box 27, 00014 Helsinki, Finland.
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Várnai A, Viikari L, Marjamaa K, Siika-aho M. Adsorption of monocomponent enzymes in enzyme mixture analyzed quantitatively during hydrolysis of lignocellulose substrates. Bioresour Technol 2011; 102:1220-7. [PMID: 20736135 DOI: 10.1016/j.biortech.2010.07.120] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2010] [Revised: 07/28/2010] [Accepted: 07/29/2010] [Indexed: 05/03/2023]
Abstract
The adsorption of purified Trichoderma reesei cellulases (TrCel7A, TrCel6A and TrCel5A) and xylanase TrXyn11 and Aspergillus niger β-glucosidase AnCel3A was studied in enzyme mixture during hydrolysis of two pretreated lignocellulosic materials, steam pretreated and catalytically delignified spruce, along with microcrystalline cellulose (Avicel). The enzyme mixture was compiled to resemble the composition of commercial cellulase preparations. The hydrolysis was carried out at 35 °C to mimic the temperature of the simultaneous saccharification and fermentation (SSF). Enzyme adsorption was followed by analyzing the activity and the protein amount of the individual free enzymes in the hydrolysis supernatant. Most enzymes adsorbed quickly at early stages of the hydrolysis and remained bound throughout the hydrolysis, although the conversion reached was fairly high. Only with the catalytically oxidized spruce samples, the bound enzymes started to be released as the hydrolysis degree reached 80%. The results based on enzyme activities and protein assay were in good accordance.
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Affiliation(s)
- Anikó Várnai
- University of Helsinki, Food and Environmental Sciences, P.O. Box 27, 00014 Helsinki, Finland.
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Penttilä PA, Várnai A, Leppänen K, Peura M, Kallonen A, Jääskeläinen P, Lucenius J, Ruokolainen J, Siika-aho M, Viikari L, Serimaa R. Changes in Submicrometer Structure of Enzymatically Hydrolyzed Microcrystalline Cellulose. Biomacromolecules 2010; 11:1111-7. [DOI: 10.1021/bm1001119] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Paavo A. Penttilä
- Departments of Physics and Food and Environmental Sciences, University of Helsinki, Helsinki, Finland, Departments of Biomedical Engineering and Computational Science and Applied Physics, Aalto University School of Science and Technology, Espoo, Finland, and VTT Technical Research Centre of Finland, Espoo, Finland
| | - Anikó Várnai
- Departments of Physics and Food and Environmental Sciences, University of Helsinki, Helsinki, Finland, Departments of Biomedical Engineering and Computational Science and Applied Physics, Aalto University School of Science and Technology, Espoo, Finland, and VTT Technical Research Centre of Finland, Espoo, Finland
| | - Kirsi Leppänen
- Departments of Physics and Food and Environmental Sciences, University of Helsinki, Helsinki, Finland, Departments of Biomedical Engineering and Computational Science and Applied Physics, Aalto University School of Science and Technology, Espoo, Finland, and VTT Technical Research Centre of Finland, Espoo, Finland
| | - Marko Peura
- Departments of Physics and Food and Environmental Sciences, University of Helsinki, Helsinki, Finland, Departments of Biomedical Engineering and Computational Science and Applied Physics, Aalto University School of Science and Technology, Espoo, Finland, and VTT Technical Research Centre of Finland, Espoo, Finland
| | - Aki Kallonen
- Departments of Physics and Food and Environmental Sciences, University of Helsinki, Helsinki, Finland, Departments of Biomedical Engineering and Computational Science and Applied Physics, Aalto University School of Science and Technology, Espoo, Finland, and VTT Technical Research Centre of Finland, Espoo, Finland
| | - Pentti Jääskeläinen
- Departments of Physics and Food and Environmental Sciences, University of Helsinki, Helsinki, Finland, Departments of Biomedical Engineering and Computational Science and Applied Physics, Aalto University School of Science and Technology, Espoo, Finland, and VTT Technical Research Centre of Finland, Espoo, Finland
| | - Jessica Lucenius
- Departments of Physics and Food and Environmental Sciences, University of Helsinki, Helsinki, Finland, Departments of Biomedical Engineering and Computational Science and Applied Physics, Aalto University School of Science and Technology, Espoo, Finland, and VTT Technical Research Centre of Finland, Espoo, Finland
| | - Janne Ruokolainen
- Departments of Physics and Food and Environmental Sciences, University of Helsinki, Helsinki, Finland, Departments of Biomedical Engineering and Computational Science and Applied Physics, Aalto University School of Science and Technology, Espoo, Finland, and VTT Technical Research Centre of Finland, Espoo, Finland
| | - Matti Siika-aho
- Departments of Physics and Food and Environmental Sciences, University of Helsinki, Helsinki, Finland, Departments of Biomedical Engineering and Computational Science and Applied Physics, Aalto University School of Science and Technology, Espoo, Finland, and VTT Technical Research Centre of Finland, Espoo, Finland
| | - Liisa Viikari
- Departments of Physics and Food and Environmental Sciences, University of Helsinki, Helsinki, Finland, Departments of Biomedical Engineering and Computational Science and Applied Physics, Aalto University School of Science and Technology, Espoo, Finland, and VTT Technical Research Centre of Finland, Espoo, Finland
| | - Ritva Serimaa
- Departments of Physics and Food and Environmental Sciences, University of Helsinki, Helsinki, Finland, Departments of Biomedical Engineering and Computational Science and Applied Physics, Aalto University School of Science and Technology, Espoo, Finland, and VTT Technical Research Centre of Finland, Espoo, Finland
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Roszol L, Várnai A, Lorántfy B, Noszticzius Z, Wittmann M. Negative salt effect in an acid-base diode: Simulations and experiments. J Chem Phys 2010; 132:064902. [DOI: 10.1063/1.3292001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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