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Glycoside Hydrolase Family 146
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- Author: ^^^Jonathon Briggs^^^
- Responsible Curator: ^^^Harry Gilbert^^^
| Glycoside Hydrolase Family GH146 | |
| Clan | GH-A |
| Mechanism | retaining |
| Active site residues | known |
| CAZy DB link | |
| https://www.cazy.org/GH146.html | |
Substrate specificities
This glycoside hydrolase family has only one assigned activity to date, β-arabinofuranosidease. The founding member of this family, BT_0349, was shown to cleave both β1,2- and β1,3-linked arabinofuranose sidechains present in branched sugar beet arabinan [1].
Kinetics and Mechanism
The only characterised GH146 enzyme, BT_0349 displays exo-activity on β-linked arabinofuranose by deploying a retaining mechanism, based on identification of catalytic residues [1].
Catalytic Residues
The catalytic nucleophile and general acid/base residues of the founding member of GH146, BT_0349, were identified as Cys414 and Glu318, respectively [1].
Three-dimensional structures
The crystal structure of BT_0349, solved using SAD methods to a resolution of 2.1 A, revealed a four-domain structure. The N-terminal catalytic domain comprises an (α/ α)5 barrel followed by three β-sandwich domains (1, 2 & 3). An arabinofuranose is present in the active site pocket of the catalytic domain, while a zinc atom is coordinated by three cystines and a glutamate in the same domain. The catalytic apparatus is completely conserved with GH127, however GH127 lacks β-sandwich domain 3 which is positioned over the active site, effectively burying the bound arabinofuranose [1].
Family Firsts
- First stereochemistry determination
- BT_0349 from B. thetaiotaomicron [1].
- First catalytic nucleophile identification
- BT_0349 from B. thetaiotaomicron [1].
- First general acid/base residue identification
- BT_0349 from B. thetaiotaomicron [1].
- First 3-D structure
- BT_0349 from B. thetaiotaomicron [1].
References
- Luis AS, Briggs J, Zhang X, Farnell B, Ndeh D, Labourel A, Baslé A, Cartmell A, Terrapon N, Stott K, Lowe EC, McLean R, Shearer K, Schückel J, Venditto I, Ralet MC, Henrissat B, Martens EC, Mosimann SC, Abbott DW, and Gilbert HJ. (2018). Dietary pectic glycans are degraded by coordinated enzyme pathways in human colonic Bacteroides. Nat Microbiol. 2018;3(2):210-219. DOI:10.1038/s41564-017-0079-1 |