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The aerobic hyperthermophile“Fervidibacter sacchari”catabolizes diverse polysaccharides and is the only cultivated member of the class“Fervidibacteria”within the phylumArmatimonadota. It encodes 117 putative glycoside hydrolases (GHs), including two from GH family 50 (GH50). In this study, we expressed, purified, and functionally characterized one of these GH50 enzymes, Fsa16295Glu. We show that Fsa16295Glu is a β-1,3-endoglucanase with optimal activity on carboxymethyl curdlan (CM-curdlan) and only weak agarase activity, despite most GH50 enzymes being described as β-agarases. The purified enzyme has a wide temperature range of 4–95°C (optimal 80°C), making it the first characterized hyperthermophilic representative of GH50. The enzyme is also active at a broad pH range of at least 5.5–11 (optimal 6.5–10). Fsa16295Glu possesses a relatively highkcat/KMof 1.82 × 107 s−1M−1with CM-curdlan and degrades CM-curdlan nearly completely to sugar monomers, indicating preferential hydrolysis of glucans containing β-1,3 linkages. Finally, a phylogenetic analysis of Fsa16295Glu and all other GH50 enzymes revealed that Fsa16295Glu is distant from other characterized enzymes but phylogenetically related to enzymes from thermophilic archaea that were likely acquired horizontally from“Fervidibacteria.”Given its functional and phylogenetic novelty, we propose that Fsa16295Glu represents a new enzyme subfamily, GH50_3.
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This content will become publicly available on October 1, 2026
Characterization of the thermophilic xylanase Fsa02490Xyn from the hyperthermophile Fervidibacter sacchari belonging to glycoside hydrolase family 10
Fervidibacter sacchariis an aerobic hyperthermophile belonging to the phylumArmatimonadotathat degrades a variety of polysaccharides. Its genome encodes 117 enzymes with one or more annotated glycoside hydrolase (GH) domain, but the roles of these putative GHs in polysaccharide catabolism are poorly defined. Here, we describe oneF. saccharienzyme encoding a GH10 domain, Fsa02490Xyn, that was previously shown to be active onMiscanthus, oat β‐glucan, and beech‐wood xylan, with optimal activity at 90–100 °C. We show that Fsa02490Xyn is also active on birch‐wood xylan and gellan gum. The pH range on beech‐wood xylan was 4.5 to 9.5 (pHopt7.0–8.0). Fsa024940Xyn had aKmof 2.375 mm,Vmaxof 1250 μm·min−1, andkcat/Kmof 1.259 × 104 s−1·m−1when using apara‐nitrophenyl‐𝛽‐xylobioside assay. A phylogenetic analysis of GH10 family enzymes revealed a large clade of enzymes from diverse members of the classFervidibacteria, including Fsa02490Xyn and a second enzyme fromF. sacchari, with apparent horizontal gene transfer withinFervidibacteriaand betweenFervidibacteriaand thermophilicBacillota. This study establishes Fsa02490Xyn as a hyperthermophilic GH10 enzyme with endo‐β‐1,4‐xylanase activity and identifies a large clade of homologous GH10 enzymes within the classFervidibacteria. Impact statementThe depolymerization of xylan at high temperatures is important because this process limits the degradation of polysaccharides in nature and the synthesis of biofuels from plant wastes. Our study is also important becauseF. sacchariis one of only a few cultivated members of theArmatimonadota, which are polysaccharide‐degradation specialists.
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- PAR ID:
- 10650800
- Publisher / Repository:
- John Wiley & Sons Ltd.
- Date Published:
- Journal Name:
- FEBS Open Bio
- Volume:
- 15
- Issue:
- 10
- ISSN:
- 2211-5463
- Page Range / eLocation ID:
- 1629 to 1642
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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