Glycoside Hydrolase Family 194

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• Author: Masahiro Nakajima
• Responsible Curator: Masahiro Nakajima

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Glycoside Hydrolase Family GH194
Clan	GH-S
Mechanism	inverting
Active site residues	not known
CAZy DB link
https://www.cazy.org/GH194.html

Substrate specificities

PgSGL3(H744_1c0222, KEGG) from Photobacterium gaetbulicola is specific to β-1,2-glucan among polysaccharides. The enzyme hydrolyzes β-1,2-glucan endolytically to produce β-1,2-glucooligosaccharides. PgSGL3 preferentially produce β-1,2-glucooctasaccharide at the initial stage of hydrolysis of β-1,2-glucan.

Kinetics and Mechanism

PgSGL3 follows anomer-inverting mechanism, which is determined by measuring change in optical rotation during hydrolysis of β-1,2-glucan [1].

Catalytic Residues

E214(PgSGL3) is the putative general acid as this residue is structurally well-superimposed with the general acid (E262) in GH162 β-1,2-glucanase from Talaromyces funiculosus [2]. E214Q mutant shows drastic decrease in catalytic activity compared to the wild-type enzyme [1]. E214 is also conserved across other GH-S clan families including GH144, GH192, and GH193.
Similarly, D148 (PgSGL3) is one of the candidate for the general base as this residue is a spatially conserved residue shared with several β-1,2-glucanases; GH144 (from Chitinophaga pinensis and Xanthomonas campestris pv. campestris), GH192 (from P. gaetbulicala), GH193 (from Sanguibacter keddieii) [1, 2]. However, no complex structure with a substrate is available.

Three-dimensional structures

A ligand-free structure of PgSGL3 is available [1].

Family Firsts

First stereochemistry 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 P. gaetbulicola using the iodide single-wavelength anomalous diffraction phasing method.

References

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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 |
3. 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 |