Abstract
BackgroundEfficient degradation of lignocellulosic biomass has become a major bottleneck in industrial processes which attempt to use biomass as a carbon source for the production of biofuels and materials. To make the most effective use of the source material, both the hemicellulosic as well as cellulosic parts of the biomass should be targeted, and as such both hemicellulases and cellulases are important enzymes in biorefinery processes. Using thermostable versions of these enzymes can also prove beneficial in biomass degradation, as they can be expected to act faster than mesophilic enzymes and the process can also be improved by lower viscosities at higher temperatures, as well as prevent the introduction of microbial contamination.ResultsThis study presents the investigation of the thermostable, dual-function xylanase-glucuronoyl esterase enzyme CkXyn10C-GE15A from the hyperthermophilic bacterium Caldicellulosiruptor kristjanssonii. Biochemical characterization of the enzyme was performed, including assays for establishing the melting points for the different protein domains, activity assays for the two catalytic domains, as well as binding assays for the multiple carbohydrate-binding domains present in CkXyn10C-GE15A. Although the enzyme domains are naturally linked together, when added separately to biomass, the expected boosting of the xylanase action was not seen. This lack of intramolecular synergy might suggest, together with previous data, that increased xylose release is not the main beneficial trait given by glucuronoyl esterases.ConclusionsDue to its thermostability, CkXyn10C-GE15A is a promising candidate for industrial processes, with both catalytic domains exhibiting melting temperatures over 70 °C. Of particular interest is the glucuronoyl esterase domain, as it represents the first studied thermostable enzyme displaying this activity.
Highlights
Recent trends in industrial biofuel and biomaterial production have been focused on the use of lignocellulosic plant biomass—composed mainly of cellulose, hemicelluloses, and lignin—as a renewable feedstock to produceKrska and Larsbrink Biotechnol Biofuels (2020) 13:68 the desired end products [1]
Backbone or other sugars are linked to lignin in so-called lignin–carbohydrate complexes (LCCs), which pose another challenge in extraction of sugars by increasing the cell wall recalcitrance to degradation [9, 10]
We have investigated a novel enzyme, CkXyn10C-GE15A, which consists of seven individual Carbohydrate-active enzyme (CAZyme) domains: two catalytic domains (GH10 xylanase and carbohydrate esterase family 15 (CE15) glucuronoyl esterase) and five Carbohydrate-binding module (CBM)
Summary
Recent trends in industrial biofuel and biomaterial production have been focused on the use of lignocellulosic plant biomass—composed mainly of cellulose, hemicelluloses, and lignin—as a renewable feedstock to produceKrska and Larsbrink Biotechnol Biofuels (2020) 13:68 the desired end products [1]. Depending on the source of the plant biomass the proportion of these components vary, but typically hemicelluloses make up between 25–40% of the dry plant material in industrial crops [1,2,3,4] In both hardwood trees and grasses, the most abundant hemicellulose is xylan, comprising between 15–50% of the cell dry weight of the plant, and approximately one-third of all renewable organic carbon on earth [1,2,3, 5, 6]. Efficient degradation of lignocellulosic biomass has become a major bottleneck in industrial processes which attempt to use biomass as a carbon source for the production of biofuels and materials. Using thermostable versions of these enzymes can prove beneficial in biomass degradation, as they can be expected to act faster than mesophilic enzymes and the process can be improved by lower viscosities at higher temperatures, as well as prevent the introduction of microbial contamination
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