Glycoside Hydrolase Family 158

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: ^^^Kazune Tamura^^^
• Responsible Curator: ^^^Harry Brumer^^^

---

Glycoside Hydrolase Family GH158
Clan	GH-A
Mechanism	retaining
Active site residues	known
CAZy DB link
https://www.cazy.org/GH158.html

Substrate specificities

Members of family 158 have been shown to display activity towards β(1,3)-glucans, making it the fourth clan GH-A family known to contain β(1,3)-glucanase activity, alongside GH17, GH128, and GH148. The founding member of this family, Vvad_PD1638 from Victivallis vadensis, was shown to be active on carboxymethyl-curdlan in a high-throughput screen [1].

BuGH158 from the prominent human gut symbiont Bacteroides uniformis was the first GH158 member to receive detailed characterization [2]. BuGH158 is an endo β(1,3)-glucanase with high specificity towards laminarin from Laminaria digitata, a β(1,3)-glucan with single β(1,6)-glucose branches. BuGH158 is unable to tolerate more extensive branching as evidenced by poor activity towards other β(1,3)-glucans with longer, more frequent branches like laminarin from Eisenia bicyclis and yeast β-glucan [2]. The unbranched, linear β(1,3)-glucan curdlan was also not effectively hydrolyzed by BuGH158, due the glucans poor solubility in water (Vvad_PD1638 described above was active on a curdlan proxy that was chemically modified to increase water-solubility [1]).

Kinetics and Mechanism

As a family within clan GH-A, GH158 members were inferred to be retaining enzymes. Retention of anomeric stereochemistry was experimentally confirmed by ¹H NMR on the product of hydrolysis of 2-chloro-4-nitrophenyl laminaribioside by BuGH158 from Bacteroides uniformis [2]. As such, these enzymes follow the classical Koshland double-displacement mechanism, which proceed via a covalent glycosyl-enzyme intermediate.

Catalytic Residues

The catalytic nucleophile and catalytic acid/base residues of BuGH158 were determined to be E220 and E137 [2]. This glutamate pair is located on loops immediately following beta-strands 7 (nucleophile) and 4 (acid/base), consistent with all other clan GH-A enzymes.

Three-dimensional structures

The X-ray crystal structure of BuGH158 from Bacteroides uniformis determined by multi-wavelength anomalous dispersion represents the founding structural representative of this family [2]. The 1.8 A structure reveal in addition to an N-terminal (a/b)8 TIM barrel domain, which is a hallmark of clan GH-A structures, a C-terminal eight-stranded immunoglobulin (Ig)-like domain that makes extensive contacts with the TIM barrel. A loop from the Ig-like domain extends over the TIM barrel to shape the active site cleft.

Family Firsts

First stereochemistry determination

Content is to be added here.

First catalytic nucleophile identification

Content is to be added here.

First general acid/base residue identification

Content is to be added here.

First 3-D structure

Content is to be added here.

References

1. Helbert W, Poulet L, Drouillard S, Mathieu S, Loiodice M, Couturier M, Lombard V, Terrapon N, Turchetto J, Vincentelli R, and Henrissat B. (2019). Discovery of novel carbohydrate-active enzymes through the rational exploration of the protein sequences space. Proc Natl Acad Sci U S A. 2019;116(13):6063-6068. DOI:10.1073/pnas.1815791116 |

3. Davies, G.J. and Sinnott, M.L. (2008) Sorting the diverse: the sequence-based classifications of carbohydrate-active enzymes. The Biochemist, vol. 30, no. 4., pp. 26-32. Download PDF version.