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Table 1 Classification of glycoside hydrolases (GH) family consisting of xylanase

From: A detailed overview of xylanases: an emerging biomolecule for current and future prospective

GH family Clan Activities in family Properties Mode of action References
Structure Functional
GH 5 GH-A endo-β-1,4-Xylanase; β-glucosidase cellulase Consist of seven amino acid
(β/α)8 barrel fold
Highly conserved
Largest GH family
Substitute on main xylan chain
CNB-Glu
CPD-Glu
Retaining
Collins et al. (2005), Lombard et al. (2014)
GH 7 GH-B endo-β-1,4-Glucanase High-molecular weight and low pI
β-Jelly roll
small substrate-binding site (4 subsite and 1 catalytic site)
Common characteristics with family 10 and 11 CNB-Glu
CPD-Glu
Retaining
Collins et al. (2005), Lombard et al. (2014)
GH 8 GH-M Cellulases; chitosanases; lichenases; endo-1,4-β-xylanases (α/α)6 fold
Large substrate-binding cleft
Cold-adapted
Break xylan into X3 and X4
Highly active on long-chain XOS
CNB-Asp
CPD-Glu
Inversion of the anomeric
Collins et al. (2002, 2005), Lombard et al. (2014)
GH 10 Family G GH-A endo-1,4-β-Xylanases; endo-1,3-β-xylanases Low-molecular mass high pI (8–9.5)
(α/β)8 barrel fold
Small yet numerous (4–5) substrate-binding sites
Attack on aryl β-glycosides and aglyconic bond of X2 and X3, respectively
Highly active on short XOS
CNB-Glu
CPD-Glu
Retaining
Ahmed et al. (2009), Collins et al. (2005), Lombard et al. (2014), Motta et al. (2013)
GH11 GH-C xylanases “true xylanases” (active on xylose substrate) High MW and lower pI values
β-Jelly roll
Small size
Large substrate-binding clefts (7 subsites)
Attack on aryl β-glycosides and aglyconic bond of X2 and X3, respectively
Inactive on aryl cellobiosides
High substrate selectivity and catalytic efficiency
Wide pH and temperature stability
Cold-adapted
Highly active on long-chain XOS
CNB-Glu
CPD-Glu
Retaining
Ahmed et al. (2009), Collins et al. (2005), Lombard et al. (2014), Motta et al. (2013)
GH 43 GH-F β-Xylosidase
α-l-Arabinofuranosidase; xylanase
β-Propeller (5 blade) fold
Catalytic residue glutamate and aspartate in the center
Debranching and degradation of hemicellulose polymer CNB-Asp
CPD-Glu
Inverting single displacement mechanism
Collins et al. (2005), Lombard et al. (2014), Mewis et al. (2016)
  1. X2, xylobiose; X3, xylotriose; X4, xylotetraose; XOS, xylooligosaccharides; CNB, catalytic nucleophile/base; CPD, catalytic proton donor; Asp, aspartic acid; Glu, glutamic acid