Glycoside Hydrolase Family 135

This page is currently under construction. This means that the Responsible Curator has deemed that the page's content is not quite up to CAZypedia's standards for full public consumption. All information should be considered to be under revision and may be subject to major changes.

• Author: ^^^Spencer Williams^^^
• Responsible Curator: ^^^Spencer Williams^^^

---

Glycoside Hydrolase Family GH135
Clan	none
Mechanism	unknown
Active site residues	known/not known
CAZy DB link
https://www.cazy.org/GH135.html

Substrate specificities

A single report has disclosed fungal glycoside hydrolases with the ability to degrade a fungal heteropolysaccharide galactosaminogalactan (GAG) [1]. GAG is produced by Aspergillus fumigatus as an exopolysaccharide, and is comprised of a linear heterogeneous polysaccharide containing α-1,4-linked galactose, N-acetylgalactosamine, and galactosamine residues, and which is found in both a secreted form and bound to the cell wall of hyphae [2]. The recombinant protein hydrolyzed purified and cell wall-associated GAG. While it is unclear precisely where within the GAG chain the enzyme acts, and thus whether it should be considered an α-galactosidase, α-galactosaminase (i.e. cleaving an α-galactosamine linkage) or an N-acetyl-α-galactosaminidase, and 3-D complex of the protein with N-acetylgalactosamine (see below) is suggestive that the enzyme possesses α-galactosaminidase activity.

Kinetics and Mechanism

Very little is known about the kinetics or mechanism of this enzyme, owing to the lack of homogeneous, well-defined substrates. No activity was detected using a range of simple 4-nitrophenyl glycosides [1]. Instead, the cleavage GAG by Sph3 could be monitored by release of reducing ends. It is not known whether the enzyme hydrolyzes substrate with retention or inversion of anomeric configuration.

Catalytic Residues

Structural and sequence alignments identified three conserved acidic amino acid residues, Asp166, Glu167, and Glu222 (numbering for Aspergillus clavatus), which were located within the putative active site groove. Mutagenesis of these residues individually either decreased or abolished the catalytic activity of Sph3 towards purified GAG. The D166A, D166N, and E167A variants displayed no significant activity. The E222A variant displayed no activity, while the E222Q variant retained 60% of wild-type activity.

Three-dimensional structures

Three-dimensional structures are available for one GH family 135 member, Aspergillus clavatus Sph3 [1]. This protein has a classical (β/α)₈ TIM barrel fold, with two small additional helices, one on either end of the sixth α helix. This fold was described as sharing similarities with enzymes belonging to families GH18, GH27, and GH84.

Family Firsts

First stereochemistry determination

Unknown.

First catalytic nucleophile identification

Unknown.

First general acid/base residue identification

Unknown.

First 3-D structure

Sph3 from Aspergillus clavatus [1].

References

1. Bamford NC, Snarr BD, Gravelat FN, Little DJ, Lee MJ, Zacharias CA, Chabot JC, Geller AM, Baptista SD, Baker P, Robinson H, Howell PL, and Sheppard DC. (2015). Sph3 Is a Glycoside Hydrolase Required for the Biosynthesis of Galactosaminogalactan in Aspergillus fumigatus. J Biol Chem. 2015;290(46):27438-50. DOI:10.1074/jbc.M115.679050 |
2. Fontaine T, Delangle A, Simenel C, Coddeville B, van Vliet SJ, van Kooyk Y, Bozza S, Moretti S, Schwarz F, Trichot C, Aebi M, Delepierre M, Elbim C, Romani L, and Latgé JP. (2011). Galactosaminogalactan, a new immunosuppressive polysaccharide of Aspergillus fumigatus. PLoS Pathog. 2011;7(11):e1002372. DOI:10.1371/journal.ppat.1002372 |