Glycoside Hydrolase Family 18

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• Author: ^^^Gideon Davies^^^
• Responsible Curator: ^^^Gideon Davies^^^

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Glycoside Hydrolase Family GH18
Clan	GH-K
Mechanism	retaining
Active site residues	known (acid/neighbouring group)
CAZy DB link
http://www.cazy.org/fam/GH18.html

Substrate specificities

GH18 is unusual in having both catalytically active chitinase (EC 3.2.1.14) and endo-β-N-acetylglucosaminidases (EC 3.2.1.96) but there are also sub-families of non-hydrolytic proteins that function as carbohydrate binding modules / "lectins" or as xylanase inhibitors.

Kinetics and Mechanism

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Catalytic Residues

The catalytically active GH18 enzymes use a double displacement reaction mechanism with "neighbouring group participation".

Three-dimensional structures

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Family Firsts

First sterochemistry determination

Often incorrectly reported as inverting, this family performs catalysis with retention of anomeric configuration as first shown on the Bacillus ciculans enzyme [1].

First catalytic nucleophile identification

This family si one of many that uses neighboruing group participation for catalysis with the N-acetyl carbonyl group acting as the nucleophile; first proposed (I believe) for this family in [2].

First general acid/base residue identification

On the basis of 3-D structure [3].

First 3-D structure

The first two 3-D structures for GH18 members were the Serratia marcescens chitinase A and the plant defence protein hevamine published "back-to-back" in Structure in 1994 [3, 4].

References

1. Armand S, Tomita H, Heyraud A, Gey C, Watanabe T, and Henrissat B. (1994). Stereochemical course of the hydrolysis reaction catalyzed by chitinases A1 and D from Bacillus circulans WL-12. FEBS Lett. 1994;343(2):177-80. DOI:10.1016/0014-5793(94)80314-5 |
2. Terwisscha van Scheltinga AC, Armand S, Kalk KH, Isogai A, Henrissat B, and Dijkstra BW. (1995). Stereochemistry of chitin hydrolysis by a plant chitinase/lysozyme and X-ray structure of a complex with allosamidin: evidence for substrate assisted catalysis. Biochemistry. 1995;34(48):15619-23. DOI:10.1021/bi00048a003 |
3. Perrakis A, Tews I, Dauter Z, Oppenheim AB, Chet I, Wilson KS, and Vorgias CE. (1994). Crystal structure of a bacterial chitinase at 2.3 A resolution. Structure. 1994;2(12):1169-80. DOI:10.1016/s0969-2126(94)00119-7 |
5. Terwisscha van Scheltinga AC, Kalk KH, Beintema JJ, and Dijkstra BW. (1994). Crystal structures of hevamine, a plant defence protein with chitinase and lysozyme activity, and its complex with an inhibitor. Structure. 1994;2(12):1181-9. DOI:10.1016/s0969-2126(94)00120-0 |
6. Robert V. Stick and Spencer J. Williams. (2009) Carbohydrates. Elsevier Science.

7. Sinnott, M.L. (1990) Catalytic mechanisms of enzymic glycosyl transfer. Chem. Rev. 90, 1171-1202. DOI: 10.1021/cr00105a006