Glycoside Hydrolase Family 44

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• Author: ^^^Peter Reilly^^^
• Responsible Curator: ^^^Peter Reilly^^^

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Glycoside Hydrolase Family GH44
Clan	None specified, but Kitago et al. [1] and Nam et al. [2] suggest that it belongs to Clan GH-A.
Mechanism	Retaining
Active site residues	Catalytic proton donor/acceptor: Glu; catalytic nucleophile: Glu
CAZy DB link
https://www.cazy.org/GH44.html

Substrate specificities

Active on many substances, including cellooligosaccharides of DP4 and longer, carboxymethylcellulose, xylan, lichenan, Avicel (slightly), and xyloglucan, which appears to be a prime substrate [4,5].

Kinetics and Mechanism

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Catalytic Residues

Clostridium thermocellum endoglucanase: catalytic proton donor/acceptor: Glu186; catalytic nucleophile: Glu359 [1]. Protein from metagenomic library: catalytic proton donor/acceptor: Glu221; catalytic nucleophile: Glu393 [2].Clostridium acetobutylicum endoglucanase: catalytic proton donor/acceptor: Glu180; catalytic nucleophile: Glu352 [3].

Three-dimensional structures

The first three-dimensional structure was by Kitago et al. [1], who found a TIM-like barrel domain and a beta-sandwich domain in C. thermocellum endoglucanase. Similar structures were found by Nam et al. [2] in a protein from a metagenomic library and Warner et al. [3] in C. acetobutylicum endoglucanase. Ca and Zn ions are found as ligands [1].

Family Firsts

First stereochemistry determination

Kitago et al. [1] found that C. thermocellum endoglucanase acts by a retaining mechanism. They observed that a beta-anomer was preferentially formed during cyclohexaitol hydrolysis.

First catalytic nucleophile identification

Kitago et al. [1], by testing activity of the C. thermocellum endoglucanase E359Q mutant.

First general acid/base residue identification

Kitago et al. [1], by testing activity of the C. thermocellum endoglucanase E186Q mutant.

First 3-D structure

Kitago et al. [1] of C. thermocellum endoglucanase. It had a resolution of 0.96 Å and allowed the identification of the catalytic residues and the mechanism.

References

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5. Warner CD, Go RM, García-Salinas C, Ford C, and Reilly PJ. 2010b. Kinetic characterization of a glycoside hydrolase family 44 endoglucanase from Ruminococcus flavefaciens FD-1. Submitted for publication.