Abstract
Xylanolytic enzymes have a broad range of applications in industrial biotechnology as biocatalytic components of various processes and products, such as food additives, bakery products, coffee extraction, agricultural silage and functional foods. An increasing market demand has driven the growing interest for the discovery of xylanases with specific industrially relevant characteristics, such as stability at elevated temperatures and in the presence of other denaturing factors, which will facilitate their incorporation into industrial processes. In this work, we report the discovery and biochemical characterization of a new thermostable GH10 xylanase, termed XynDZ5, exhibiting only 26% amino acid sequence identity to the closest characterized xylanolytic enzyme. This new enzyme was discovered in an Icelandic hot spring enrichment culture of a Thermoanaerobacterium species using a recently developed bioinformatic analysis platform. XynDZ5 was produced recombinantly in Escherichia coli, purified and characterized biochemically. This analysis revealed that it acts as an endo-1,4-β-xylanase that performs optimally at 65–75°C and pH 7.5. The enzyme is capable of retaining high levels of catalytic efficiency after several hours of incubation at high temperatures, as well as in the presence of significant concentrations of a range of metal ions and denaturing agents. Interestingly, the XynDZ5 biochemical profile was found to be atypical, as it also exhibits significant exo-activity. Computational modeling of its three-dimensional structure predicted a (β/α)8 TIM barrel fold, which is very frequently encountered among family GH10 enzymes. This modeled structure has provided clues about structural features that may explain aspects of its catalytic performance. Our results suggest that XynDZ5 represents a promising new candidate biocatalyst appropriate for several high-temperature biotechnological applications in the pulp, paper, baking, animal-feed and biofuel industries.
Highlights
Hemicelluloses comprise almost one third of all renewable organic matter on the planet and are the most abundant biopolymer group after cellulose (Saha, 2003; Soni et al, 2018). 20–40% of the hemicellulose content is xylan, an amorphous structural polysaccharide found in both hardwood and annual plants (Basit et al, 2018)
Among the 2,822 putative protein-encoding genes obtained, 94 CAZy hits were detected, which corresponded to 53 distinct CAZy families: 29 glycoside hydrolases (GH), ten glycosyl transferases (GTs), four carbohydrate esterases (CEs), one polysaccharide lyase (PL) and nine carbohydrate-binding modules (CBMs)
Members of the families of glycoside hydrolases GH3, GH5, GH10, GH26 and GH51 can putatively act as endo-1,4-β-xylanases (E.C. 3.2.1.8), members of the family GH26 can act as endo-1,3-β- xylanases (E.C 3.2.1.32), while members of the families GH1, GH3, GH5, GH39, GH51, GH52 and GH120 contain putative 1,4-β-xylosidases (E.C. 3.2.137)
Summary
Hemicelluloses comprise almost one third of all renewable organic matter on the planet and are the most abundant biopolymer group after cellulose (Saha, 2003; Soni et al, 2018). 20–40% of the hemicellulose content is xylan, an amorphous structural polysaccharide found in both hardwood and annual plants (Basit et al, 2018). Xylanolytic enzymes are produced by organisms that are capable of utilizing pentoses, mainly xylose and arabinose, as carbon sources. Endo-β-1,4-xylanases (EC 3.2.1.8) are the glycoside hydrolases (GH) that cleave the inner β-1,4 bonds between two xylose monomers in the xylan backbone and xylo-oligosaccharides (XOs) (Chakdar et al, 2016). The GH10 family includes mainly endo-1,4-β-xylanases originating from all three domains of life. They exhibit versatile substrate specificity, as they are often able to hydrolyse low-molecular-weight cellulosic substrates (Juturu and Wu, 2012). Contrary to GH10, most GH11 family enzymes are fungal and bacterial endo-β-1,4xylanases (EC 3.2.1.8) that cleave internal β-1,4-xylosidic bonds, acting exclusively on D-xylose-containing substrates without hydrolytic activity against cellulose. GH11 xylanases typically fold into a β-jelly roll architecture (Paes et al, 2012)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
