Glycoside Hydrolase Family 129

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• Author: ^^^Hisashi Ashida^^^
• Responsible Curator: ^^^Shinya Fushinobu^^^

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Glycoside Hydrolase Family GH129
Clan	none
Mechanism	retaining
Active site residues	not known
CAZy DB link
https://www.cazy.org/GH129.html

Substrate specificities

This family of glycoside hydrolases was established based on the α-N-acetylgalactosaminidase (NagBb) from Bifidobacterium bifidum JCM 1254, which shows slight sequence similarity with GH101 endo-α-N-acetylgalactosaminidases [1]. NagBb acts more rapidly on GalNAcα1-pNP than Galβ1-3GalNAcα1-pNP, therefore its substrate specificity is quite different from GH101 enzymes (EC 3.2.1.97). This specificity is also different from those of previously known exo-α-N-acetylgalactosaminidases (EC 3.2.1.49) in GH27, GH36 and GH109. As such, NagBb may be appropriately referred to as a exo/endo-α-N-acetylgalactosaminidase.

NagBb most preferably hydrolyzes GalNAcα1-Ser, a minimal structure of Tn antigen on mucin-type glycoproteins, suggesting that NagBb might be involved in degradation of intestinal mucins. The members of GH129 are distributed in several bifidobacterial species such as B. longum subsp. longum, B. longum subsp. infants and B. breve, which are frequently found in intestines of infants.

Kinetics and Mechanism

NagBb is a retaining enzyme. The stereochemistry of hydrolysis has been monitored by normal-phase HPLC using GalNAcα1-pNP as a substrate [1]. GH129 is distantly related to GH101 as well as GH13 α-amylases; members of these latter two families are also classified as retaining enzymes.

Catalytic Residues

Asp-435 in NagBb is predicted as catalytic nucleophile by remote homology-based fold recognition using GH13 α-amylase 1 (TVAI) from Thermoactinomyces vulgaris R-47 (PDB code 1JI1) as a template [1]. Asp-330 in NagBb may be the so-called "fixer": analogous to the third invariant catalytic residue conserved in GH101 and GH13 enzymes, which is proposed as a transition-state stabilizer. The general acid/base residue is in GH129 unknown.

Three-dimensional structures

Currently not determined experimentally.

Family Firsts

First stereochemistry determination

NagBb from Bifidobacterium bifidum JCM 1254 by normal-phase HPLC [1].

First catalytic nucleophile identification

To be determined experimentally.

First general acid/base residue identification

To be determined experimentally.

First 3-D structure

To be determined experimentally.

References

1. Kiyohara M, Nakatomi T, Kurihara S, Fushinobu S, Suzuki H, Tanaka T, Shoda SI, Kitaoka M, Katayama T, Yamamoto K, and Ashida H. (2012). α-N-acetylgalactosaminidase from infant-associated bifidobacteria belonging to novel glycoside hydrolase family 129 is implicated in alternative mucin degradation pathway. J Biol Chem. 2012;287(1):693-700. DOI:10.1074/jbc.M111.277384 |