Glycoside Hydrolase Family 128

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• Author: ^^^Yuichi Sakamoto^^^
• Responsible Curator: ^^^Yuichi Sakamoto^^^

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Glycoside Hydrolase Family GH128
Clan	GH-x
Mechanism	retaining/inverting
Active site residues	known/not known
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

A GH128 enzyme, GLU1, catalyzed depolymerization of glucans composed of β-1,3-linked main chains, and reaction product analysis indicated that the enzyme had an endolytic mode. The optimal pH and temperature of the enzyme for laminarin were pH 4 and at 50 °C, respectively. From the result of the three-dimensional structure prediction, GLU1 would be categorized to GH-A clan in CAZy server. Therefore, it have been inferred that GH 128 enzymes are retaining enzymes [1].

Catalytic Residues

From the sequence alignment of GH128 members, two conserved glutamic acids, E103 and E195 in GLU1, were expected to perform as the catalytic residues

Three-dimensional structures

The deduced sequence of GLU1 was used to predict three-dimensional structure using the Phyre server (http://www.sbg.bio.ic.ac.uk/~phyre/; 9). The result indicated that the three-dimensional structure of GLU1 matches some (b/a)8 TIM barrel structures, such as GH39 b-xylosidase (Q9ZFM2) and GH5 b-mannanase (Q4W8M3). Therefore, GH128 would be categorized to GH-A clan [1].

Family Firsts

First stereochemistry determination

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First catalytic nucleophile identification

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First general acid/base residue identification

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First 3-D structure

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References

1. Sakamoto Y, Nakade K, and Konno N. (2011). Endo-β-1,3-glucanase GLU1, from the fruiting body of Lentinula edodes, belongs to a new glycoside hydrolase family. Appl Environ Microbiol. 2011;77(23):8350-4. DOI:10.1128/AEM.05581-11 |