Catalytic NodB homology domain of Streptomyces lividans acetylxylan esterase and its bacterial homologs
This family is represented by Streptomyces lividans acetylxylan esterase (SlAXE, EC 3.1.1.72), a member of the carbohydrate esterase 4 (CE4) superfamily. SlAXE deacetylates O-acetylated xylan, a key component of plant cell walls. It shows no detectable activity on generic esterase substrates including para-nitrophenyl acetate. It is specific for sugar-based substrates and will precipitate acetylxylan as a result of deacetylation. SlAXE also functions as a chitin and chitooligosaccharide de-N-acetylase with equal efficiency to its activity on xylan. SlAXE forms a dimer. Each monomer contains a catalytic NodB homology domain with the same overall topology and a deformed (beta/alpha)8 barrel fold as other CE4 esterases, which encompasses a mononuclear metalloenzyme employing a conserved His-His-Asp zinc-binding triad closely associated with the conserved catalytic base (aspartic acid) and acid (histidine), to carry out acid/base catalysis. SlAXE possess a single metal center with a chemical preference for Co2+.
Jiyao W et al.(2023). "The conserved domain database in 2023.",