Glycosyl hydrolase family 43, beta-D-xylosidases and arabinofuranosidases
This glycosyl hydrolase family 43 (GH43) subgroup includes mostly enzymes that have been annotated as having beta-1,4-xylosidase (beta-D-xylosidase;xylan 1,4-beta-xylosidase; EC 3.2.1.37) activity, including Selenomonas ruminantium beta-D-xylosidase SXA. These are part of an array of hemicellulases that are involved in the final breakdown of plant cell-wall whereby they degrade xylan. They hydrolyze beta-1,4 glycosidic bonds between two xylose units in short xylooligosaccharides. It also includes various GH43 family GH43 arabinofuranosidases (EC 3.2.1.55) including Humicola insolens alpha-L-arabinofuranosidase AXHd3, Bacteroides ovatus alpha-L-arabinofuranosidase (BoGH43, XynB), and the bifunctional Phanerochaete chrysosporium xylosidase/arabinofuranosidase (Xyl;PcXyl). GH43 are inverting enzymes (i.e. they invert the stereochemistry of the anomeric carbon atom of the substrate) that have an aspartate as the catalytic general base, a glutamate as the catalytic general acid and another aspartate that is responsible for pKa modulation and orienting the catalytic acid. Many GH43 enzymes display both alpha-L-arabinofuranosidase and beta-D-xylosidase activity using aryl-glycosides as substrates. A common structural feature of GH43 enzymes is a 5-bladed beta-propeller domain that contains the catalytic acid and catalytic base. A long V-shaped groove, partially enclosed at one end, forms a single extended substrate-binding surface across the face of the propeller.
Jiyao W et al.(2023). "The conserved domain database in 2023.",