Glycoside Hydrolase Family 79

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• Author: Hitomi Ichinose and Satoshi Kaneko
• Responsible Curator: Satoshi Kaneko

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Glycoside Hydrolase Family GH79
Clan	GH-A
Mechanism	retaining
Active site residues	known
CAZy DB link
https://www.cazy.org/GH79.html

Substrate specificities

Family GH79 glycoside hydrolases are found widely distributed in bacteria and eukaryota including fungi, plants, and animals. The characterized activities of this family include β-glucuronidase (EC 3.2.1.31) [1], β-4-O-methyl-glucuronidase (EC 3.2.1.-) [2], baicalin β-glucuronidase (EC 3.2.1.167) [3], heparanase (EC 3.2.1.166) [4, 5, 6, 7, 8] and hyaluronidase (EC 3.2.1.-) [9]. GH79s are involved in the metabolism of proteoglycans, such as heparan sulfate proteoglycan, chondroitin sulfate proteoglycan, and hyaluronan from animals and arabinogalactan-proteins from higher plants.

Some GH79 β-glucuronidases have been shown to release both glucuronic acid (GlcA) and 4-O-methyl-GlcA from arabinogalactan proteins [2, 10]. The Aspergillus niger enzyme shows high activity for 4-O-methyl-GlcA residues [2]. Scutellaria baicalensis β-glucuronidase hydrolyzes baicalein 7-O-β-glucuronide, which is a major flavone of S. baicalensis [3]. Heparanase is an endo-β-glucuronidase that degrades the heparan sulfate side chains of heparan sulfate proteoglycans. Heparanases are found in mammals such as human, mouse (Mus musculus), rat (Rattus norvegicus), cattle (Bos indicus), and chicken (Gallus gallus).

Kinetics and Mechanism

GH79 β-glucuronidases are retaining enzymes, as first demonstrated by ¹-NMR studies of the hydrolysis of p-nitrophenyl β-glucuronide by a β-glucuronidase from Acidobacterium capsulatum [11].

Catalytic Residues

The catalytic residues were first identified in the A. capsulatum β-glucuronidase as Glu173 (general acid/base) and Glu287 (catalytic nucleophile) by trapping of the 2-fluoroglucuronyl-enzyme intermediate and site-directed mutagenesis studies [11].

Three-dimensional structures

The three-dimensional structure of A. capsulatum β-glucuronidase solved using X-ray crystallography represented the first structure of an enzyme of GH79 (PDB IDs 3vny, 3vnz, 3vo0) [11]. The catalytic domain of the enzyme is a (β/α)₈ TIM-barrel fold, as found for all members of clan GH-A.

Family Firsts

First stereochemistry determination

Acidobacterium capsulatum β-glucuronidase by ¹H-NMR [11].

First catalytic nucleophile identification

A. capsulatum β-glucuronidase by 2-fluoroglucuroic acid labeling and the mutagenesis study [11].

First general acid/base residue identification

A. capsulatum β-glucuronidase by structural identification and the mutagenesis study [11].

First 3-D structure

A. capsulatum β-glucuronidase (PDB IDs 3vny, 3vnz, 3vo0) [11].

References

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