Sequence-based classification of glycoside hydrolases

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• Authors: ^^^Steve Withers^^^, ^^^Spencer Williams^^^
• Responsible Curator: ^^^Spencer Williams^^^

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Sequence-based classification

Sequence classification methods require knowledge of at least part of the amino acid sequence for an enzyme. Algorithmic methods are then used to compare sequences. Each of the resulting families contain proteins that are related by sequence, and by corollary, 3D fold. An obvious shortcoming of sequence-based classifications is that they can only be applied to proteins for which sequence information is available. On the other hand sequence-based classification schemes allow classification of proteins for which no biochemical evidence has been obtained such as the thousands of uncharacterized glycosidase-related sequences that originate from genome sequencing efforts worldwide. Sequence based classification methods are rather different (and in many ways complimentary) to the Enzyme Commission classification scheme, which assigns proteins to groups based on the nature of the reactions that they catalyze.

Classification of glycoside hydrolases

Using a combination of comparison algorithms the glycoside hydrolases have been classified into more than 100 GH families [1]. This classification is permanently available through the Carbohydrate Active enZyme database [2]. Classification of glycoside hydrolases into families allows many useful predictions to be made since it has long been noted that the catalytic machinery and molecular mechanism is conserved for the vast majority of the GH families [3] as well as the geometry around the glycosidic bond (irrespective of naming conventions) [4].

Classification of glycoside hydrolases into 'clans'

Classification of families into larger groups, termed 'clans', has been proposed [5]. A `clan' is a group of families that possess significant similarity in their tertiary structure, catalytic residues and mechanism. Thus knowledge of 3D structure and the functional assignment of catalytic residues is required for classification into clans. Families within clans are thought to have a common evolutionary ancestry. For an updated table of glycoside hydrolase clans see the CAZy Database [6].

References

1. Henrissat B (1991). A classification of glycosyl hydrolases based on amino acid sequence similarities. Biochem J. 1991;280 ( Pt 2)(Pt 2):309-16. DOI:10.1042/bj2800309 |

2. Carbohydrate Active Enzymes database; URL http://www.cazy.org/

3. Gebler J, Gilkes NR, Claeyssens M, Wilson DB, Béguin P, Wakarchuk WW, Kilburn DG, Miller RC Jr, Warren RA, and Withers SG. (1992). Stereoselective hydrolysis catalyzed by related beta-1,4-glucanases and beta-1,4-xylanases. J Biol Chem. 1992;267(18):12559-61. | Google Books | Open Library
4. Henrissat B, Callebaut I, Fabrega S, Lehn P, Mornon JP, and Davies G. (1995). Conserved catalytic machinery and the prediction of a common fold for several families of glycosyl hydrolases. Proc Natl Acad Sci U S A. 1995;92(15):7090-4. DOI:10.1073/pnas.92.15.7090 |
5. Henrissat B and Bairoch A. (1996). Updating the sequence-based classification of glycosyl hydrolases. Biochem J. 1996;316 ( Pt 2)(Pt 2):695-6. DOI:10.1042/bj3160695 |

6. Carbohydrate Active Enzymes database, glycoside hydrolase classification; URL http://www.cazy.org/Glycoside-Hydrolases.html