Glycosyl hydrolase family 43, such as Bacteroides ovatus alpha-L-arabinofuranosidase (BoGH43, XynB)
This glycosyl hydrolase family 43 (GH43) subgroup includes enzymes that have been characterized to have alpha-L-arabinofuranosidase (EC 3.2.1.55) and beta-1,4-xylosidase (beta-D-xylosidase;xylan 1,4-beta-xylosidase; EC 3.2.1.37) activities. Beta-1,4-xylosidases 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. These 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. Also included in this subfamily are Bacteroides ovatus alpha-L-arabinofuranosidases, BoGH43A and BoGH43B, both having a two-domain architecture, consisting of an N-terminal 5-bladed beta-propeller domain harboring the catalytic active site, and a C-terminal beta-sandwich domain. However, despite significant functional overlap between these two enzymes, BoGH43A and BoGH43B share just 41% sequence identity. The latter appears to be significantly less active on the same substrates, suggesting that these paralogs may play subtly different roles during the degradation of xyloglucans from different sources, or may function most optimally at different stages in the catabolism of xyloglucan oligosaccharides (XyGOs), for example before or after hydrolysis of certain side-chain moieties. It also includes Phanerochaete chrysosporium BKM-F-1767 Xyl, a bifunctional xylosidase/arabinofuranosidase. 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.
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