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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:
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. [DaviesSinnott2008]
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."
