GH11

GH11 is a glycoside hydrolase family designated as family 11 in the CAZy database. It comprises endo-beta-1,4-xylanases that catalyze the hydrolysis of xylan, a major hemicellulose component of plant cell walls, into xylo-oligosaccharides and xylose. Members are typically secreted by fungi and bacteria and function extracellularly in plant cell wall deconstruction.

Structure: GH11 enzymes are generally small single-domain proteins, around 200 amino acids, adopting a beta-jelly-roll fold. The active site contains two catalytic glutamate residues that mediate acid/base and nucleophilic roles. The substrate-binding cleft is long and shallow, favoring binding of linear xylans and accommodating unsubstituted regions of xylan.

Substrate specificity and mechanism: They hydrolyze internal beta-1,4-xylosidic linkages in xylan. Substitution on xylan (arabinosyl, acetyl, feruloyl groups) can hinder activity. They release xylo-oligosaccharides rather than just xylose. Optima vary by enzyme but many GH11 xylanases are active around pH 5–7 and temperatures of 40–60°C; thermostable variants exist.

Relation to other GH families and modules: GH11 is distinct from GH10 xylanases in having a smaller, single-domain beta-jelly-roll architecture and typically a higher affinity for unsubstituted xylan. Some GH11 enzymes are secreted as catalytic modules fused to carbohydrate-binding modules (CBMs) such as CBM1, aiding attachment to plant cell walls.

Distribution and applications: GH11 xylanases are found in fungal genera such as Trichoderma and Aspergillus and in bacteria such as Bacillus. They have industrial relevance in pulp and paper bleaching, animal feed, and bioconversion of lignocellulosic biomass, where they act in concert with other enzymes to degrade hemicellulose.