Glycoside Hydrolase Family 74

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• Author: ^^^Katsuro Yaoi^^^ and ^^^Takuya Ishida^^^
• Responsible Curator: ^^^Katsuro Yaoi^^^

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Glycoside Hydrolase Family GH74
Clan	none, 7-fold β-propeller
Mechanism	inverting
Active site residues	known
CAZy DB link
http://www.cazy.org/GH74.html

Substrate specificities

Glycoside hydrolases of this family hydrolyze β-1,4-linkages of various glucans. With one exception of Cel74 from Thermotoga maritima, all biochemically characterized enzymes are specific toward xyloglucans and/or xyloglucan-oligosaccharides. Cel74 from Thermotoga maritima have highest activity on barley β-glucan, but still have 20% activity on xyloglucan. A wide diversity in mode of action by GH-74 enzymes have been reported. Oligxyloglucan reducing end-specific cellobiohydrolase from Geotrichum sp. M128, OXG-RCBH (EC 3.2.1.150) and oligoxyloglucan reducing end-specific xyloglucanobiohydrolase from Emericella nidulans formerly known as Aspergillus nidulans(OREX) are active on only xyloglucan oligosaccharides and have no ability to degrade xyloglucan polymer. They release oligosaccharides with two glucose units from non-reducing end of xyloglucan oligosaccharides [1]. On the other hands, GH-74 enzymes designated as xyloglucanase; xyloglucan specific endo-β-1,4-glucanases: XEG; and xyloglucan hydrolases: Xgh, (EC 3.2.1.151), exhibit endo-type activity on xyloglucan from tamarind seed which is well investigated xyloglucan. Many of GH-74 xyloglucanases hydrolyze glycosidic linkage of unbranched glucose residue, but several members including OXG-RCBH, OREX, and Cel74A from Hypocrea jecorina formerly known as Trichoderma reesei are accommodated to accept the side-chain xylose residues at active site.

Kinetics and Mechanism

Family 74 enzymes are inverting enzymes, as shown by NMR analysis on Xeg74 from Thermobifida fusca and XEG from Geotrichum sp. M128.

Catalytic Residues

Crystal structure of OXG-RCBH demonstrated that Asp35 and Asp465 are located in the middle of the binding cleft, and its crucial roles in hydrolytic activity were experimentally confirmed by using site-directed mutagenesis [2]. The corresponding Asp residues in Clostridium thermocellum are nicely located between subsite -1 and +1 in the complex structure [3].

Three-dimensional structures

Over all structure of GH-74 enzymes consist of a tandem repeat of two seven-bladed β-propeller domains. The two domains form a open cleft substrate binding site at the interface. Catalytic residues are located in the middle of the cleft. One side of the binding cleft of OXG-RCBH are blocked by 'exo-loop' which is found only in exo-acting enzyme in this family. Crystal structure of complex with xyloglucan oligo-saccharides elucidated the interaction towards side-chain of the substrate by the enzymes [2, 3].

Family Firsts

First stereochemistry determination

Xeg74 from Thermobifida fusca by ¹H-NMR [4].

First gene cloning

EglC from Aspergillus niger [5].

First general acid residue identification

OXG-RCBH from Geotrichum sp. M128 [2].

First general base residue identification

OXG-RCBH from Geotrichum sp. M128 [2].

First 3-D structure

OXG-RCBH from Geotrichum sp. M128 [2].

References

1. 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. 2002;277(50):48276-81. DOI:10.1074/jbc.M208443200 |
2. 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. 2004;12(7):1209-17. DOI:10.1016/j.str.2004.04.020 |
3. 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. 2006;281(34):24922-33. DOI:10.1074/jbc.M603583200 |
4. 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. 2003;270(14):3083-91. DOI:10.1046/j.1432-1033.2003.03695.x |
5. 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. 2002;68(4):1556-60. DOI:10.1128/AEM.68.4.1556-1560.2002 |