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Peciulyte A, Samuelsson L, Olsson L, McFarland KC, Frickmann J, Østergård L, Halvorsen R, Scott BR, Johansen KS. Redox processes acidify and decarboxylate steam-pretreated lignocellulosic biomass and are modulated by LPMO and catalase. BIOTECHNOLOGY FOR BIOFUELS 2018; 11:165. [PMID: 29946356 PMCID: PMC6004669 DOI: 10.1186/s13068-018-1159-z] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Accepted: 05/31/2018] [Indexed: 05/07/2023]
Abstract
BACKGROUND The bioconversion of lignocellulosic feedstocks to ethanol is being commercialised, but further process development is required to improve their economic feasibility. Efficient saccharification of lignocellulose to fermentable sugars requires oxidative cleavage of glycosidic linkages by lytic polysaccharide monooxygenases (LPMOs). However, a proper understanding of the catalytic mechanism of this enzyme class and the interaction with other redox processes associated with the saccharification of lignocellulose is still lacking. The in-use stability of LPMO-containing enzyme cocktails is increased by the addition of catalase implying that hydrogen peroxide (H2O2) is generated in the slurry during incubation. Therefore, we sought to characterize the effects of enzymatic and abiotic sources of H2O2 on lignocellulose hydrolysis to identify parameters that could improve this process. Moreover, we studied the abiotic redox reactions of steam-pretreated wheat straw as a function of temperature and dry-matter (DM) content. RESULTS Abiotic reactions in pretreated wheat straw consume oxygen, release carbon dioxide (CO2) to the slurry, and decrease the pH. The magnitude of these reactions increased with temperature and with DM content. The presence of LPMO during saccharification reduced the amount of CO2 liberated, while the effect on pH was insignificant. Catalase led to increased decarboxylation through an unknown mechanism. Both in situ-generated and added H2O2 caused a decrease in pH. CONCLUSIONS Abiotic redox processes similar to those that occur in natural water-logged environments also affect the saccharification of pretreated lignocellulose. Heating of the lignocellulosic material and adjustment of pH trigger rapid oxygen consumption and acidification of the slurry. In industrial settings, it will be of utmost importance to control these processes. LPMOs interact with the surrounding redox compounds and redirect abiotic electron flow from decarboxylating reactions to fuel the oxidative cleavage of glycosidic bonds in cellulose.
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Affiliation(s)
- Ausra Peciulyte
- Division of Industrial Biotechnology, Department of Biology and Biological Engineering, Chalmers University of Technology, Kemivägen 10, 412 96 Gothenburg, Sweden
| | - Louise Samuelsson
- Division of Industrial Biotechnology, Department of Biology and Biological Engineering, Chalmers University of Technology, Kemivägen 10, 412 96 Gothenburg, Sweden
| | - Lisbeth Olsson
- Division of Industrial Biotechnology, Department of Biology and Biological Engineering, Chalmers University of Technology, Kemivägen 10, 412 96 Gothenburg, Sweden
| | | | - Jesper Frickmann
- Novozymes North America, 77 Perry’s Chapel Church Road, Franklinton, NC 27525 USA
| | | | | | | | - Katja S. Johansen
- Division of Industrial Biotechnology, Department of Biology and Biological Engineering, Chalmers University of Technology, Kemivägen 10, 412 96 Gothenburg, Sweden
- Novozymes A/S, Krogshøjvej 36, 2880 Bagsværd, Denmark
- Department of Geosciences and Natural Resource Management, Copenhagen University, Rolighedsvej 23, 1958 Frederiksberg, Denmark
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Di Russo NV, Condurso HL, Li K, Bruner SD, Roitberg AE. Oxygen diffusion pathways in a cofactor-independent dioxygenase. Chem Sci 2015; 6:6341-6348. [PMID: 26508997 PMCID: PMC4618494 DOI: 10.1039/c5sc01638j] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A combination of experimental and computational studies reveals the main O2 diffusion pathways, providing insight into how cofactor-independent oxygenases control stereospecificity and prevent oxidative inactivation.
Molecular oxygen plays an important role in a wide variety of enzymatic reactions. Through recent research efforts combining computational and experimental methods a new view of O2 diffusion is emerging, where specific channels guide O2 to the active site. The focus of this work is DpgC, a cofactor-independent oxygenase. Molecular dynamics simulations, together with mutagenesis experiments and xenon-binding data, reveal that O2 reaches the active site of this enzyme using three main pathways and four different access points. These pathways connect a series of dynamic hydrophobic pockets, concentrating O2 at a specific face of the enzyme substrate. Extensive molecular dynamics simulations provide information about which pathways are more frequently used. This data is consistent with the results of kinetic measurements on mutants and is difficult to obtain using computational cavity-location methods. Taken together, our results reveal that although DpgC is rare in its ability of activating O2 in the absence of cofactors or metals, the way O2 reaches the active site is similar to that reported for other O2-using proteins: multiple access channels are available, and the architecture of the pathway network can provide regio- and stereoselectivity. Our results point to the existence of common themes in O2 access that are conserved among very different types of proteins.
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Affiliation(s)
- Natali V Di Russo
- Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA
| | - Heather L Condurso
- Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA
| | - Kunhua Li
- Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA
| | - Steven D Bruner
- Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA
| | - Adrian E Roitberg
- Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA
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