Glycosyl hydrolase family 43 protein such as Bacteroides thetaiotaomicron VPI-5482 arabinofuranosidase Bt3655. This glycosyl hydrolase family 43 (GH43)-like family includes the characterized arabinofuranosidases (EC 3.2.1.55): Bacteroides thetaiotaomicron VPI-5482 (Bt3655;BT_3655) and Penicillium chrysogenum 31B Abf43B, as well as Bifidobacterium adolescentis ATCC 15703 beta-xylosidase (EC 3.2.1.37) BAD_1527. It belongs to the glycosyl hydrolase clan F (according to carbohydrate-active enzymes database (CAZY)) which includes family 43 (GH43) and 62 (GH62) families. GH43 includes enzymes with beta-xylosidase (EC 3.2.1.37), beta-1,3-xylosidase (EC 3.2.1.-), alpha-L-arabinofuranosidase (EC 3.2.1.55), arabinanase (EC 3.2.1.99), xylanase (EC 3.2.1.8), endo-alpha-L-arabinanases (beta-xylanases) and galactan 1,3-beta-galactosidase (EC 3.2.1.145) activities. 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.

Glycosyl hydrolase families 43 and 62 form CAZY clan GH-F. This glycosyl hydrolase clan F (according to carbohydrate-active enzymes database (CAZY)) includes family 43 (GH43) and 62 (GH62). GH43 includes enzymes with beta-xylosidase (EC 3.2.1.37), beta-1,3-xylosidase (EC 3.2.1.-), alpha-L-arabinofuranosidase (EC 3.2.1.55), arabinanase (EC 3.2.1.99), xylanase (EC 3.2.1.8), endo-alpha-L-arabinanases (beta-xylanases) and galactan 1,3-beta-galactosidase (EC 3.2.1.145) activities. GH62 includes enzymes characterized as arabinofuranosidases (alpha-L-arabinofuranosidases; EC 3.2.1.55) that specifically cleave either alpha-1,2 or alpha-1,3-L-arabinofuranose side chains from xylans. 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 of the enzymes in this family display both alpha-L-arabinofuranosidase and beta-D-xylosidase activity using aryl-glycosides as substrates. GH62 are also predicted to be inverting enzymes. A common structural feature of both, GH43 and GH62 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.

Glycosyl hydrolase family 43 protein; uncharacterized. This glycosyl hydrolase family 43 (GH43)-like subfamily includes uncharacterized enzymes similar to those with beta-1,4-xylosidase (xylan 1,4-beta-xylosidase; EC 3.2.1.37), beta-1,3-xylosidase (EC 3.2.1.-), alpha-L-arabinofuranosidase (EC 3.2.1.55), arabinanase (EC 3.2.1.99), xylanase (EC 3.2.1.8), endo-alpha-L-arabinanase and galactan 1,3-beta-galactosidase (EC 3.2.1.145) activities. 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. Many of the enzymes in this family 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.

Glycosyl hydrolase family 43 protein such as Geobacillus stearothermophilus endo-alpha-1,5-L-arabinanase AbnA. This glycosyl hydrolase family 43 (GH43) subgroup includes mostly enzymes with alpha-L-arabinofuranosidase (ABF; EC 3.2.1.55) and endo-alpha-L-arabinanase (ABN; EC 3.2.1.99) activities. It includes Geobacillus stearothermophilus T-6 NCIMB 40222 AbnA, Bacillus subtilis subsp. subtilis str. 168 (Abn2;YxiA;J3A;BSU39330) (Arb43B), and Thermotoga petrophila RKU-1 (AbnA;TpABN;Tpet_0637). 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. The GH43 ABN enzymes hydrolyze alpha-1,5-L-arabinofuranoside linkages while the ABF enzymes cleave arabinose side chains so that the combined actions of these two enzymes reduce arabinan to L-arabinose and/or arabinooligosaccharides. Many of these enzymes are different from other arabinases; they are organized into two different domains with a divalent metal cluster close to the catalytic residues to guarantee the correct protonation state of the catalytic residues and consequently the enzyme activity. These arabinan-degrading enzymes are important in the food industry for efficient production of L-arabinose from agricultural waste; L-arabinose is often used as a bioactive sweetener. 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.

Glycosyl hydrolase family 43 such as Fibrobacter succinogenes subsp. succinogenes S85 arabinoxylan alpha-L-arabinofuranosidase. This glycosyl hydrolase family 43 (GH43) 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. They 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. This subfamily includes the characterized Clostridium stercorarium F-9 beta-xylosidase Xyl43B. It also includes Humicola insolens AXHd3 (HiAXHd3), a GH43 arabinofuranosidase (EC 3.2.1.55) that hydrolyzes O3-linked arabinose of doubly substituted xylans, a feature of the polysaccharide that is recalcitrant to degradation. It possesses an additional C-terminal beta-sandwich domain such that the interface between the domains comprises a xylan binding cleft that houses the active site pocket. The HiAXHd3 active site is tuned to hydrolyze arabinofuranosyl or xylosyl linkages, and the topology of the distal regions of the substrate binding surface confers specificity. It also includes Fibrobacter succinogenes subsp. succinogenes S85 arabinoxylan alpha-L-arabinofuranosidase (Axh1;Fisuc_1769;FSU_2269), Paenibacillus sp. E18 alpha-L-arabinofuranosidase (Abf43A), Bifidobacterium adolescentis ATCC 15703 double substituted xylan alpha-1,3-L-specific arabinofuranosidase d3 (AXHd3;AXH-d3;BaAXH-d3;BAD_0301;E-AFAM2), and Chrysosporium lucknowense C1 arabinoxylan hydrolase / double substituted xylan alpha-1,3-L-arabinofuranosidase (Abn7;AXHd). 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.