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Glycoside Hydrolase Family 74
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|Glycoside Hydrolase Family GH74|
|Clan||none, 7-fold β-propeller|
|Active site residues||known|
|CAZy DB link|
Glycoside hydrolases of this family hydrolyze β-1,4-linkages of various glucans. With the exception of Cel74 from Thermotoga maritima, all biochemically characterized enzymes are specific toward xyloglucans and/or xyloglucan-oligosaccharides. Cel74 from Thermotoga maritima exhibits the highest activity on barley β-glucan, with relative activity of 20% toward xyloglucan . A wide diversity in the modes of action by GH74 enzymes has been reported. "Oligoxyloglucan reducing end-specific cellobiohydrolase (OXG-RCBH, EC 188.8.131.52)" from Geotrichum sp. M128  and "oligoxyloglucan reducing end-specific xyloglucanobiohydrolase (OREX)" from Emericella nidulans (formerly known as Aspergillus nidulans)  are active on only xyloglucan oligosaccharides and have essentially no ability to degrade xyloglucan polysaccharides. They release oligosaccharides with two glucose units from non-reducing end of xyloglucan oligosaccharides. On the other hand, GH74 enzymes designated as xyloglucanase; xyloglucan specific endo-β-1,4-glucanases: XEG; and xyloglucan hydrolases: Xgh, (EC 184.108.40.206), exhibit endo-type activity on xyloglucan from tamarind seed, a readily available and well-investigated xyloglucan . Many GH74 xyloglucanases hydrolyze the glycosidic linkage of unbranched glucose residues, but several members including Geotrichum sp. OXG-RCBH , E. nidulans OREX , and Hypocrea jecorina (formerly known as Trichoderma reesei) Cel74A  accommodate side-chain xylose residues at subsite -1 of the active site.
Kinetics and Mechanism
Crystal structure of OXG-RCBH demonstrated that Asp35 and Asp465 are located in the middle of the binding cleft, and their crucial roles in hydrolytic activity were experimentally confirmed by site-directed mutagenesis . However, their identities as general acid and general base were not assigned. The corresponding Asp residues in Xgh74A from Clostridium thermocellum are nicely located between subsites -1 and +1 in the complex structure with xyloglucan-derived oligosaccharides .
Overall structures of GH74 enzymes consist of a tandem repeat of two seven-bladed β-propeller domains. The two domains form a substrate binding cleft at the interface. The catalytic residues are located in the middle of this cleft. One side of the binding cleft of OXG-RCBH is blocked by a so-called 'exo-loop' which is found only in exo-acting enzymes in this family . A crystal structure of a complex with xyloglucan-derived oligosaccharides elucidated the interaction with the side-chains of the substrate by these enzymes .
- First stereochemistry determination
- Xeg74 from Thermobifida fusca by 1H-NMR .
- First gene cloning
- The first gene cloned was AviIII from Aspergillus aculeatus , and the first xyloglucanase activity was confirmed by the study on EglC from Aspergillus niger .
- First general acid residue identification
- Xgh74A from Clostridium thermocellum .
- First general base residue identification
- Xgh74A from Clostridium thermocellum .
- First 3-D structure
- OXG-RCBH from Geotrichum sp. M128 .
- Chhabra SR and Kelly RM. (2002) Biochemical characterization of Thermotoga maritima endoglucanase Cel74 with and without a carbohydrate binding module (CBM). FEBS Lett. 531, 375-80.
- Yaoi K and Mitsuishi Y. (2002) Purification, characterization, cloning, and expression of a novel xyloglucan-specific glycosidase, oligoxyloglucan reducing end-specific cellobiohydrolase. J Biol Chem. 277, 48276-81. DOI:10.1074/jbc.M208443200 |
- Bauer S, Vasu P, Mort AJ, and Somerville CR. (2005) Cloning, expression, and characterization of an oligoxyloglucan reducing end-specific xyloglucanobiohydrolase from Aspergillus nidulans. Carbohydr Res. 340, 2590-7. DOI:10.1016/j.carres.2005.09.014 |
- York WS, Harvey LK, Guillen R, Albersheim P, and Darvill AG. (1993) Structural analysis of tamarind seed xyloglucan oligosaccharides using beta-galactosidase digestion and spectroscopic methods. Carbohydr Res. 248, 285-301.
- Desmet T, Cantaert T, Gualfetti P, Nerinckx W, Gross L, Mitchinson C, and Piens K. (2007) An investigation of the substrate specificity of the xyloglucanase Cel74A from Hypocrea jecorina. FEBS J. 274, 356-63. DOI:10.1111/j.1742-4658.2006.05582.x |
- Irwin DC, Cheng M, Xiang B, Rose JK, and Wilson DB. (2003) Cloning, expression and characterization of a family-74 xyloglucanase from Thermobifida fusca. Eur J Biochem. 270, 3083-91.
- Yaoi K, Kondo H, Noro N, Suzuki M, Tsuda S, and Mitsuishi Y. (2004) Tandem repeat of a seven-bladed beta-propeller domain in oligoxyloglucan reducing-end-specific cellobiohydrolase. Structure. 12, 1209-17. DOI:10.1016/j.str.2004.04.020 |
- Martinez-Fleites C, Guerreiro CI, Baumann MJ, Taylor EJ, Prates JA, Ferreira LM, Fontes CM, Brumer H, and Davies GJ. (2006) Crystal structures of Clostridium thermocellum xyloglucanase, XGH74A, reveal the structural basis for xyloglucan recognition and degradation. J Biol Chem. 281, 24922-33. DOI:10.1074/jbc.M603583200 |
- Takada G, Kawagushi T, Yoneda T, Kawasaki M, Sumitani JI, and Arai M. Molecular cloning and expression of the celluloytic system of Aspergillus aculeatus, p. 364-373. In Ohmiya K, Hayashi K, Sakka K, Kobayashi Y, Karita S, and Kimura T (ed.), Genetics, biochemistry and ecology of cellulose degradation. 1999 Uni Publishers, Tokyo, Japan, ISBN 4-946450-17-3.
- Hasper AA, Dekkers E, van Mil M, van de Vondervoort PJ, and de Graaff LH. (2002) EglC, a new endoglucanase from Aspergillus niger with major activity towards xyloglucan. Appl Environ Microbiol. 68, 1556-60.