Acetylxylan esterase

Function

Acetylxylan esterase (AXE) catalyzes the deacetylation of xylans and xylo-oligosaccharides. AXE is involved in the biodegradation of hemicellulose. AXE hydrolyzes the ester linkages of the acetyl groups in position 2 and/or 3 of xylose moiety of naturally acetylated xylan from hardwood. AXE is one of the accessory enzymes which are part of the xylanolytic system. Together with xylanase, β-xylosidase, α-arabinofuranosidase and methylglucoronidase, AXE is required for the complete degradation of xylan.^[1]

Relevance

Solubility of cellulose is critical for the use of this abundant biomass as biofuel. Xylan is the major constituent of hemicellulose which is the second most abundant polysaccharide in plants. Several enzymes are needed for making cellulose soluble via complete hydrolysis. Among those are cellulase, xylanase and AXE.

Structural Highlights

• Acetylxylan esterase with paraoxon inhibitor, ethylene glycol, acetate and Ca+2 ions.
• Paraoxon inhibitor binding site (3m83). ^[2]
• Ca+2 coordination site. Water molecules are shown as red spheres.

3D structures of acetylxylan esterase

Acetylxylan esterase 3D structures