Carbohydrate Binding Module 6 (CBM6); many are appended to glycoside hydrolase (GH) family 11 and GH43 xylanase domains. This family includes carbohydrate binding module 6 (CBM6) domains that are appended mainly to glycoside hydrolase (GH) family domains, including GH3, GH11, and GH43 domains. These CBM6s are non-catalytic carbohydrate binding domains that facilitate the strong binding of the GH catalytic modules with their dedicated, insoluble substrates. Examples of proteins having CMB6s belonging to this family are Microbispora bispora GghA, a 1,4-beta-D-glucan glucohydrolase (GH3); Clostridium thermocellum xylanase U (GH11), and Penicillium purpurogenum ABF3, a bifunctional alpha-L-arabinofuranosidase/xylobiohydrolase (GH43). GH3 comprises enzymes with activities including beta-glucosidase (hydrolyzes beta-galactosidase) and beta-xylosidase (hydrolyzes 1,4-beta-D-xylosidase). GH11 family comprises enzymes with xylanase (endo-1,4-beta-xylanase) activity which catalyze the hydrolysis of beta-1,4 bonds of xylan, the major component of hemicelluloses, to generate xylooligosaccharides and xylose. GH43 includes beta-xylosidases and beta-xylanases, using aryl-glycosides as substrates. CBM6 is an unusual CBM as it represents a chimera of two distinct binding sites with different modes of binding: binding site I within the loop regions and binding site II on the concave face of the beta-sandwich fold.

Cellulose Binding Domain Type IV.

Carbohydrate binding module (family 6).

Glycosyl hydrolase family 43, including Butyrivibrio proteoclasticus arabinofuranosidase Xsa43E. This glycosyl hydrolase family 43 (GH43) subgroup belongs to the GH43_AXH-like subgroup which includes enzymes that have been characterized with beta-xylosidase (EC 3.2.1.37), alpha-L-arabinofuranosidase (EC 3.2.1.55), alpha-1,2-L-arabinofuranosidase 43A (arabinan-specific; EC 3.2.1.-), endo-alpha-L-arabinanase as well as arabinoxylan arabinofuranohydrolase (AXH) 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. AXHs specifically hydrolyze the glycosidic bond between arabinofuranosyl substituents and xylopyranosyl backbone residues of arabinoxylan. This subgroup includes Cellvibrio japonicus arabinan-specific alpha-1,2-arabinofuranosidase, CjAbf43A, which confers its specificity by a surface cleft that is complementary to the helical backbone of the polysaccharide, and Butyrivibrio proteoclasticus GH43 enzyme Xsa43E, also an arabinofuranosidase, which has been shown to cleave arabinose side chains from short segments of xylan. Several of these enzymes also contain carbohydrate binding modules (CBMs) that bind cellulose or xylan. 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, includes arabinoxylan arabinofuranohydrolase, beta-xylosidase, endo-1,4-beta-xylanase, and alpha-L-arabinofuranosidase. This subgroup includes Bacillus subtilis arabinoxylan arabinofuranohydrolase (XynD;BsAXH-m23;BSU18160), Butyrivibrio proteoclasticus alpha-L-arabinofuranosidase (Xsa43E;bpr_I2319), Clostridium stercorarium alpha-L-arabinofuranosidase XylA, and metagenomic beta-xylosidase (EC 3.2.1.37) / alpha-L-arabinofuranosidase (EC 3.2.1.55) CoXyl43. It belongs to the glycosyl hydrolase clan F (according to carbohydrate-active enzymes database (CAZY)) which includes family 43 (GH43) and 62 (GH62) families. The GH43_AXH-like subgroup includes enzymes that have been characterized with beta-xylosidase, alpha-L-arabinofuranosidase, endo-alpha-L-arabinanase as well as arabinoxylan arabinofuranohydrolase (AXH) 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. AXHs specifically hydrolyze the glycosidic bond between arabinofuranosyl substituents and xylopyranosyl backbone residues of arabinoxylan. Metagenomic beta-xylosidase/alpha-L-arabinofuranosidase CoXyl43 shows synergy with Trichoderma reesei cellulases and promotes plant biomass saccharification by degrading xylo-oligosaccharides, such as xylobiose and xylotriose, into the monosaccharide xylose. Studies show that the hydrolytic activity of CoXyl43 is stimulated in the presence of calcium. Several of these enzymes also contain carbohydrate binding modules (CBMs) that bind cellulose or xylan. 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.

ChainA, ENDO-1,4-BETA-XYLANASE Y [Acetivibrio thermocellus],1GKL_B Chain B, ENDO-1,4-BETA-XYLANASE Y [Acetivibrio thermocellus],1WB4_A Chain A, Endo-1,4-beta-xylanase Y [Acetivibrio thermocellus],1WB4_B Chain B, Endo-1,4-beta-xylanase Y [Acetivibrio thermocellus],1WB5_A Chain A, Endo-1,4-beta-xylanase Y [Acetivibrio thermocellus],1WB5_B Chain B, Endo-1,4-beta-xylanase Y [Acetivibrio thermocellus],1WB6_A Chain A, ENDO-1,4-BETA-XYLANASE Y [Acetivibrio thermocellus],1WB6_B Chain B, ENDO-1,4-BETA-XYLANASE Y [Acetivibrio thermocellus]

ChainA, Endo-1,4-beta-xylanase Y [Acetivibrio thermocellus]

ChainA, Endo-1,4-beta-xylanase Y [Acetivibrio thermocellus],1GKK_B Chain B, Endo-1,4-beta-xylanase Y [Acetivibrio thermocellus],3ZI7_A Chain A, Endo-1,4-beta-xylanase Y [Acetivibrio thermocellus YS],3ZI7_B Chain B, Endo-1,4-beta-xylanase Y [Acetivibrio thermocellus YS],4BAG_A Chain A, ENDO-1,4-BETA-XYLANASE Y [Acetivibrio thermocellus],4BAG_B Chain B, ENDO-1,4-BETA-XYLANASE Y [Acetivibrio thermocellus],4H35_A Chain A, Endo-1,4-beta-xylanase Y [Acetivibrio thermocellus],4H35_B Chain B, Endo-1,4-beta-xylanase Y [Acetivibrio thermocellus],5FXM_A Chain A, Endo-1,4-beta-xylanase Y [Acetivibrio thermocellus],6Y8G_AAA Chain AAA, Endo-1,4-beta-xylanase Y [Acetivibrio thermocellus],6Y8G_BBB Chain BBB, Endo-1,4-beta-xylanase Y [Acetivibrio thermocellus]

Crystalstructure of a glycoside hydrolase family 43 arabinoxylan arabinofuranohydrolase from Bacillus subtilis. [Bacillus subtilis],3C7F_A Crystal structure of a glycoside hydrolase family 43 arabinoxylan arabinofuranohydrolase from bacillus subtilis in complex with xylotriose. [Bacillus subtilis],3C7H_A Crystal structure of glycoside hydrolase family 43 arabinoxylan arabinofuranohydrolase from Bacillus subtilis in complex with AXOS-4-0.5. [Bacillus subtilis],3C7O_A Crystal structure of a glycoside hydrolase family 43 arabinoxylan arabinofuranohydrolase from Bacillus subtilis in complex with cellotetraose. [Bacillus subtilis]

Crystalstructure of a glycoside hydrolase family 43 arabinoxylan arabinofuranohydrolase from Bacillus subtilis in complex with xylotetraose. [Bacillus subtilis]

Endo-1,4-beta-xylanase Y OS=Acetivibrio thermocellus OX=1515 GN=xynY PE=1 SV=1

Arabinoxylan arabinofuranohydrolase OS=Paenibacillus polymyxa OX=1406 GN=xynD PE=1 SV=1

Arabinoxylan arabinofuranohydrolase OS=Bacillus subtilis (strain 168) OX=224308 GN=xynD PE=1 SV=2

Xylanase/beta-glucanase OS=Ruminococcus flavefaciens OX=1265 GN=xynD PE=3 SV=2

Endo-1,4-beta-xylanase Z OS=Acetivibrio thermocellus (strain ATCC 27405 / DSM 1237 / JCM 9322 / NBRC 103400 / NCIMB 10682 / NRRL B-4536 / VPI 7372) OX=203119 GN=xynZ PE=1 SV=3