Glycoside Hydrolase Family 192

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• Author: Masahiro Nakajima
• Responsible Curator: Masahiro Nakajima

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Glycoside Hydrolase Family GH192
Clan	GH-S
Mechanism	inverting
Active site residues	not known
CAZy DB link
https://www.cazy.org/GH192.html

Substrate specificities

PgSGL1(H744_1c0224, KEGG) and PgSGL2(H744_2c1936, KEGG) from Photobacterium gaetbulicola and EeSGL1(A0A081KBI6, Uniprot) from Endozoicomonas elysicola were characterized as reported in 2025 [1]. The three enzymes specifically hydrolyze β-1,2-glucan to produce β-1,2-glucooligosaccharides in an endolytic manner [1].

Kinetics and Mechanism

Hydrolysis of β-1,2-glucan by PgSGL1 suggests that the enzyme follows anomer-inverting mechanism [1]. Analysis of the change of the degree of optical rotation during hydrolysis of β-1,2-glucan and after addition of aquaeous ammonia. Sharp decrease of the degree of optical rotation by aquaeous ammonia is the same pattern as in the case of GH162 β-1,2-glucanase from Talaromyces funiculosus (TfSGL), an anomer-inverting enzyme [2].

Catalytic Residues

E221(EeSGL1) is the putative general acid as this residue is structurally well-superimposed with the general acid (E262) in GH162 TfSGL [1, 2]. E221Q mutant shows drastic decrease in catalytic activity compared to the wild-type enzyme [1]. E221 is also conserved across other GH-S clan families including GH144, GH193, and GH194. This residue is also conserved in GH189, a family related to clan GH-S, as an acid/base catalyst [3]).
Similarly, D149(EeSGL1) is a residue conserved spatially with several β-1,2-glucanases; GH144 (from Chitinophaga pinensis and Xanthomonas campestris pv. campestris) GH193 (from Sanguibacter keddieii), and GH194 (from P. gaetbulicala) [1, 4]. D149N mutant also shows drastically decreased activity against the wild-type enzyme. However, mutational analysis alone is insufficient to definitively identify catalytic residues because a reaction mechanism of GH192 is atypical.

Three-dimensional structures

A ligand-free structure of EeSGL1 is available [1].

Family Firsts

First stereochemisty determination

A bacterial β-1,2-glucanase from P. gaetbulicola by monitoring the change in optical rotation [1].

First general base residue identification

not known.

First general acid residue identification

not known.

First 3-D structure

A bacterial β-1,2-glucanase from E. elysicola using molecular replacement [1].

References

1. Nakajima M, Tanaka N, Motouchi S, Kobayashi K, Shimizu H, Abe K, Hosoyamada N, Abara N, Morimoto N, Hiramoto N, Nakata R, Takashima A, Hosoki M, Suzuki S, Shikano K, Fujimaru T, Imagawa S, Kawadai Y, Wang Z, Kitano Y, Nihira T, Nakai H, and Taguchi H. (2025). New glycoside hydrolase families of β-1,2-glucanases. Protein Sci. 2025;34(6):e70147. DOI:10.1002/pro.70147 |
2. Tanaka N, Nakajima M, Narukawa-Nara M, Matsunaga H, Kamisuki S, Aramasa H, Takahashi Y, Sugimoto N, Abe K, Terada T, Miyanaga A, Yamashita T, Sugawara F, Kamakura T, Komba S, Nakai H, and Taguchi H. (2019). Identification, characterization, and structural analyses of a fungal endo-β-1,2-glucanase reveal a new glycoside hydrolase family. J Biol Chem. 2019;294(19):7942-7965. DOI:10.1074/jbc.RA118.007087 |
3. Tanaka N, Saito R, Kobayashi K, Nakai H, Kamo S, Kuramochi K, Taguchi H, Nakajima M, and Masaike T. (2024). Functional and structural analysis of a cyclization domain in a cyclic β-1,2-glucan synthase. Appl Microbiol Biotechnol. 2024;108(1):187. DOI:10.1007/s00253-024-13013-9 |
4. Abe K, Nakajima M, Yamashita T, Matsunaga H, Kamisuki S, Nihira T, Takahashi Y, Sugimoto N, Miyanaga A, Nakai H, Arakawa T, Fushinobu S, and Taguchi H. (2017). Biochemical and structural analyses of a bacterial endo-β-1,2-glucanase reveal a new glycoside hydrolase family. J Biol Chem. 2017;292(18):7487-7506. DOI:10.1074/jbc.M116.762724 |