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/inverting
Active site residues	known/not known
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

Content is to be added here.

Catalytic Residues

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

Three-dimensional structures

Content is to be added here.

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

Cite some reference here, with a short (1-2 senetence) explanation [2].

First general acid/base residue identification

Cite some reference here, with a short (1-2 senetence) explanation [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 [4, 5].

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

4. 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 |
6. 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 |
7. 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 |