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Glycoside Hydrolase Family 93
| Glycoside Hydrolase Family GH93 | |
| Clan | GH-E |
| Mechanism | retaining |
| Active site residues | known |
| CAZy DB link | |
| http://www.cazy.org/fam/GH93.html | |
Substrate specificities
The characterized member of family 93 are known to hydrolyse α-1,5-L-arabinan. [1],[2] EC:3.2.1-
Kinetics and Mechanism
GH93 enzymes are exoenzymes which only release arabinobiose from the non-reducing end. Net retention of the configuration of the anomeric carbon is proposed from the products of the transglycosylation activity of the protein Abnx from Penicillium chrysogenum. [1] It was recently supported in the crystal structure of the Arb93A enzyme from Fusarium graminearum in complex with arabinobiose, the degradation product of alpha-methyl-arabinotetraose. [2]
Catalytic Residues
From the crystal structure of Arb93A, Glu170 and Glu242 are proposed to act as nucleophile and acid/base respectively. Mutagenesis experiment support their role in catalysis and they are strictly conserved between the family members. [3]
Three-dimensional structures
The recent crystal structure of Arb93A reveals a six-bladed beta-propeller fold characteristic of sialidases of clan GHE. The catalytic machinery is however very different from that of sialidases. [3]
Family Firsts
First sterochemistry determination
This was determined with the Abxn enzyme using the H1-NMR technique to follow the products of its transglycosylation activity [2]
First catalytic nucleophile identification This was proposed based on the structure of Arb93A [3]
First general acid/base residue identification This was proposed based on the structure of Arb93A [3]
First 3-D structure Determined for Arb93A by Carapito and co-workers [3]
References
- Sakamoto T and Thibault JF. (2001). Exo-arabinanase of Penicillium chrysogenum able to release arabinobiose from alpha-1,5-L-arabinan. Appl Environ Microbiol. 2001;67(7):3319-21. DOI:10.1128/AEM.67.7.3319-3321.2001 |
- Carapito R, Imberty A, Jeltsch JM, Byrns SC, Tam PH, Lowary TL, Varrot A, and Phalip V. (2009). Molecular basis of arabinobio-hydrolase activity in phytopathogenic fungi: crystal structure and catalytic mechanism of Fusarium graminearum GH93 exo-alpha-L-arabinanase. J Biol Chem. 2009;284(18):12285-96. DOI:10.1074/jbc.M900439200 |
- Sakamoto T, Fujita T, and Kawasaki H. (2004). Transglycosylation catalyzed by a Penicillium chrysogenum exo-1,5-alpha-L-arabinanase. Biochim Biophys Acta. 2004;1674(1):85-90. DOI:10.1016/j.bbagen.2004.06.001 |
- Gaskell A, Crennell S, and Taylor G. (1995). The three domains of a bacterial sialidase: a beta-propeller, an immunoglobulin module and a galactose-binding jelly-roll. Structure. 1995;3(11):1197-205. DOI:10.1016/s0969-2126(01)00255-6 |