Carbohydrate-active enzymes

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• Authors: Stephen Withers, Spencer Williams, and Harry Brumer
• Responsible Curator: Spencer Williams

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Individual monosaccharide units have the potential to be joined together to form oligo- and polysaccharides, with the glycosidic linkage occurring between the anomeric position of one sugar with the hydroxyl group of another [1, 2]. Owing to the many hydroxy groups on each sugar, the potential for two possible anomeric configurations, and the possibility of different ring sizes (pyranose and furanose are the most common), there is a combinatorially-large number of structures possible [3]. Further, carbohydrates can be linked to other, non-carbohydrate molecules to generate a wide range of glycoconjugates [4]. Reflecting this structural diversity, there is a large diversity of enzymes involved in the biosynthesis, modification, binding and catabolism of carbohydrates.

The Carbohydrate Active EnZyme ("CAZy") classification

The Carbohydrate Active EnZyme (CAZy) classification is a sequence-based classification of enzymes that synthesize or break-down saccharides, which originated with the seminal grouping of glycoside hydrolases by Bernard Henrissat ([5, 6, 7, 8]; see [9] for a lucid historical review). The creation of a family requires at least one biochemically-characterized member, and is based on the concept that sequence defines protein structure, and protein structure defines function. Generally, but not exclusively, functional properties often extend to other members of the family, and provides a framework upon which to base testable hypotheses of enzyme structure and function [10]. Since its inception, the CAZy classification and associated database has undergone continually active curation, including the addition of new enzyme and associated module classes [11, 12, 13]. Hence, the CAZy classification presently comprises the following modules:

• Glycosyltransferase Families [14, 15, 16]
• Glycoside Hydrolase Families [6, 7, 8]
• Polysaccharide Lyase Families [17, 18]
• Carbohydrate Esterase Families [19, 20]
• Auxiliary Activity Families [21]
• Carbohydrate Binding Module Families (non-catalytic; included due to their association with catalytic modules) [11].

Further information on the composition of the families and mechanistic details can be obtained via these pages and the corresponding Lexicon entries.

References

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1. Robert V. Stick and Spencer J. Williams. (2009) Carbohydrates. Elsevier Science.
2. Michael Sinnott. (2007) Carbohydrate Chemistry and Biochemistry. Royal Society of Chemistry.
4. Maureen E. Taylor and Kurt Drickamer. (2011-04-21) Introduction to Glycobiology. Oxford University Press, USA.

9. Davies, G.J. and Sinnott, M.L. (2008) Sorting the diverse: the sequence-based classifications of carbohydrate-active enzymes. The Biochemist, vol. 30, no. 4., pp. 26-32. DOI:10.1042/BIO03004026.

16. Claus-Wilhelm von der Lieth, Thomas Luetteke, and Martin Frank. (2010-01-19) Bioinformatics for Glycobiology and Glycomics: An Introduction. Wiley.

    Chapter 5: Coutinho PM, Rancurel C, Stam M, Bernard T, Couto FM, Danchin EGJ, Henrissat B. "Carbohydrate-active Enzymes Database: Principles and Classification of Glycosyltransferases."