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Discovery of a Thermostable GH10 Xylanase with Broad Substrate Specificity from the Arctic Mid-Ocean Ridge Vent System.

ABSTRACT: A two-domain GH10 xylanase-encoding gene (amor_gh10a) was discovered from a metagenomic data set, generated after in situ incubation of a lignocellulosic substrate in hot sediments on the sea floor of the Arctic Mid-Ocean Ridge (AMOR). AMOR_GH10A comprises a signal peptide, a carbohydrate-binding module belonging to a previously uncharacterized family, and a catalytic glycosyl hydrolase (GH10) domain. The enzyme shares the highest sequence identity (42%) with a hypothetical protein from a Verrucomicrobia bacterium, and its GH10 domain shares low identity (24 to 28%) with functionally characterized xylanases. Purified AMOR_GH10A showed thermophilic and halophilic properties and was active toward various xylans. Uniquely, the enzyme showed high activity toward amorphous cellulose, glucomannan, and xyloglucan and was more active toward cellopentaose than toward xylopentaose. Binding assays showed that the N-terminal domain of this broad-specificity GH10 binds strongly to amorphous cellulose, as well as to microcrystalline cellulose, birchwood glucuronoxylan, barley β-glucan, and konjac glucomannan, confirming its classification as a novel CBM (CBM85).IMPORTANCE Hot springs at the sea bottom harbor unique biodiversity and are a promising source of enzymes with interesting properties. We describe the functional characterization of a thermophilic and halophilic multidomain xylanase originating from the Arctic Mid-Ocean Ridge vent system, belonging to the well-studied family 10 of glycosyl hydrolases (GH10). This xylanase, AMOR_GH10A, has a surprisingly wide substrate range and is more active toward cellopentaose than toward xylopentaose. This substrate promiscuity is unique for the GH10 family and could prove useful in industrial applications. Emphasizing the versatility of AMOR_GH10A, its N-terminal domain binds to both xylans and glycans, while not showing significant sequence similarities to any known carbohydrate-binding module (CBM) in the CAZy database. Thus, this N-terminal domain lays the foundation for the new CBM85 family.

SUBMITTER: Fredriksen L

PROVIDER: S-EPMC6414390 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description: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.

Project description:Textures and compositions of minerals can be used to infer the physiochemical conditions present within magmatic systems. Given that plagioclase is an abundant phase in many magmatic systems, understanding the link between texture and process is vital. Here, we present a database of textural and compositional data for?>?1800 plagioclase crystals in mid-ocean ridge basalt from the Gakkel Ridge (Arctic Ocean) to investigate the physiochemical conditions and processes that govern the formation of plagioclase textures and compositions. The Gakkel basalts have high modal crystal contents (up to 50%). The crystal cargo is complex, with both individual plagioclase and glomerocrysts showing large variations in crystal habit, zoning and resorption. The most common types of zoning are reverse and patchy; we attribute patchy zoning to infilling following either skeletal growth or resorption. Resorption is abundant, with multiple resorption events commonly present in a single crystal, and results from both magmatic recharge and decompression. Periods of strong undercooling, distinct to quench crystallisation, are indicated by matured skeletal crystals and thin normally zoned melt inclusion-rich bands following resorption. Individual samples often contain diverse textural and compositional plagioclase groups. Furthermore, most plagioclase is not in equilibrium with its host melt. Finally, the porous open structures of some glomerocrysts suggest that they represent pieces of entrained disaggregated mush. We interpret this to indicate that the crystal cargo is not generally phenocrystic in origin. Instead, plagioclase crystals that formed in different parts of a mush-dominated plumbing system were entrained into ascending melts. The textures of individual crystals are a function of their respective histories of (under)cooling, magma mixing and decompression. The morphologies of melt inclusion trapped in the plagioclase crystals are associated with specific host crystal textures, suggesting a link between plagioclase crystallisation processes and melt inclusion entrapment. The database of plagioclase presented herein may serve as a template for the interpretation of plagioclase textures in magmatic systems elsewhere.

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Discovery of a Thermostable GH10 Xylanase with Broad Substrate Specificity from the Arctic Mid-Ocean Ridge Vent System.

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