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Glycoside Hydrolase Family 128
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- Author: ^^^Yuichi Sakamoto^^^
- Responsible Curator: ^^^Yuichi Sakamoto^^^
| Glycoside Hydrolase Family GH128 | |
| Clan | GH-A |
| Mechanism | predicted retaining |
| Active site residues | predicted |
| CAZy DB link | |
| https://www.cazy.org/GH128.html | |
Substrate specificities
Family GH128 contains β-1,3-glucanases that cleave β-1,3 linkages in various β-glucans such as lentinan from Lentinula edodes, laminarin from Laminaria digitata, pachyman from Poria cocos, and curdlan from Alcaligenes faecalis. The first GH128 enzyme, GLU1, was cloned from L. edodes fruiting bodies (shiitake mushroom). GLU1 did not degrade β-1,3-linkages within β-1,3-1,4-glucans such as barley glucan, indicating the enzyme is categorized into EC 3.2.1.39 [1].
Kinetics and Mechanism
L. edodes GLU1 catalyzed the hydrolysis of glucans composed of β-1,3-linked main chains, and reaction product analysis indicated that the enzyme had an endo-hydrolytic mode of action. The optimal pH and temperature of the enzyme for laminarin were pH 4 and at 50 °C, respectively. Detailed mechanistic studies on GH128 have not been performed, but three-dimensional structure prediction has indicated that GLU1 is a member of Clan GH-A. As such, GH128 members are predicted to be retaining enzymes [1].
Catalytic Residues
From the sequence alignment of GH128 members, two conserved glutamic acids, E103 and E195 in L. edodes GLU1, were predicted to be the catalytic residues [1].
Three-dimensional structures
A three-dimensional structure homology model of L. edodes GLU1 indicated similarity with severl (beta/alpha)8-barrel (TIM-barrel) structures, including a GH39 beta-xylosidase and a GH5 beta-mannanase [1]. Therefore, GH128 has been included in Clan GH-A.
Family Firsts
- First stereochemistry determination
- Predicted to be retaining by membership in Clan GH-A (not experimentally verified) [1].
- First catalytic nucleophile identification
- Predicted by sequence alignment (not experimentally verified) [1].
- First general acid/base residue identification
- Predicted by sequence alignment (not experimentally verified) [1].
- First 3-D structure
- Predicted by modelling to be homologous to Clan GH-A (not experimentally verified) [1].