Glycoside Hydrolase Family 120

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• Author: ^^^Spencer Williams^^^
• Responsible Curator: ^^^Spencer Williams^^^

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Glycoside Hydrolase Family GH120
Clan	none
Mechanism	retaining
Active site residues	known
CAZy DB link
https://www.cazy.org/GH120.html

Substrate specificities

Glycoside hydrolases of family GH120 are β-xylosidases. XylC from Thermoanaerobacterium saccharolyticum hydrolyzed xylobiose and xylotriose, and aryl β-xylosides [1]. No activity was detected on oat spelt or birch wood xylans. Both T. saccharolyticum XylC and XylB from Bifidobacterium adolescentis can hydrolyze assorted aryl β-xylosides [1, 2].

Kinetics and Mechanism

Incubation of XylC from T. saccharolyticum with 4-nitrophenyl β-xyloside and alcohols including methanol, ethanol and 1-propanol resulted in the formation of the corresponding alkyl glycosides through transglycosidation [1]. The stereochemistry of 4-nitrophenyl β-xyloside hydrolysis catalyzed by XylB from Bifidobacterium adolescentis was monitored by ¹H NMR spectroscopy and revealed the initial formation of the β-anomer of xylose [2]. These data support the assignment of a retaining mechanism to these enzymes and the family, and is consistent with the enzyme utilizing a classical Koshland double-displacement mechanism.

Catalytic Residues

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Three-dimensional structures

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Family Firsts

First stereochemistry determination

Observation of transglycosylation by T. saccharolyticum XylC [1].

First catalytic nucleophile identification

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First general acid/base residue identification

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First 3-D structure

XylC from T. saccharolyticum (PDB ID 3vsv) [3].

References

1. Shao W, Xue Y, Wu A, Kataeva I, Pei J, Wu H, and Wiegel J. (2011). Characterization of a novel beta-xylosidase, XylC, from Thermoanaerobacterium saccharolyticum JW/SL-YS485. Appl Environ Microbiol. 2011;77(3):719-26. DOI:10.1128/AEM.01511-10 |
2. Cecchini DA, Fauré R, Laville E, and Potocki-Veronese G. (2015). Biochemical identification of the catalytic residues of a glycoside hydrolase family 120 β-xylosidase, involved in xylooligosaccharide metabolisation by gut bacteria. FEBS Lett. 2015;589(20 Pt B):3098-106. DOI:10.1016/j.febslet.2015.08.012 |
3. Huang CH, Sun Y, Ko TP, Chen CC, Zheng Y, Chan HC, Pang X, Wiegel J, Shao W, and Guo RT. (2012). The substrate/product-binding modes of a novel GH120 β-xylosidase (XylC) from Thermoanaerobacterium saccharolyticum JW/SL-YS485. Biochem J. 2012;448(3):401-7. DOI:10.1042/BJ20121359 |