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 enzymes are found widely distributed in bacteria and eukaryota including fungi, plants, and animals. The characterized activities of this family include β-glucuronidase (E.C. 3.2.1.31) [1], β-4-O-methyl-glucuronidase (E.C. 3.2.1.-) [2], baicalin β-glucuronidase (E.C. 3.2.1.167) [3], heparanase (E.C. 3.2.1.-) [4, 5, 6, 7, 8] and hyaluronidase (E.C. 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 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 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 proton-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 (acid/base) and Glu287 (nucleophile) by trapping of the 2-fluoroglucuronyl-enzyme intermediate and the 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 [11]. The catalytic domain of the enzyme is a (β/α)8 TIM-barrel fold as 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 [11].

References

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11. (2012) Michikawa M, Ichinose H, Mitsuru M, Peter Biely, Seino Jongkees, Makoto Yoshida, Toshihisa Kotake, Yoichi Tsumuraya, Stephen Withers, Zui Fujimoto, and Satoshi Kaneko. Structural and biochemical characterization of glycoside hydrolase family 79 β-glucuronidase from Acidobacterium capsulatum. J Biol Chem. in press.