Glycoside Hydrolases and Glycosyltransferases. Families, Modules, and Implications for Genomics

Abstract

One of the first insights into the modular nature of carbohydrate-active enzymes was provided by the dissection of a plant cell wall-degrading enzyme into two functional modules (van Tilbeurgh et al., 1986). The general architecture deduced for this protein featured two independent globular modules: a cellulase catalytic domain, responsible for the hydrolysis reaction itself, and a cellulose-binding module, devoid of catalytic activity but promoting adsorption of the enzyme onto insoluble crystalline cellulose. Similar observations were made for other polysaccharide-degrading enzymes such as plant chitinases (Lucas et al., 1985; Shinshi et al., 1990; Lerner and Raikhel, 1992). In the early 1990s it was shown that this modular structure could be deduced from sequence examination alone (Gilkes et al., 1991). It is now clear that the two major classes of carbohydrate-active enzymes, glycoside hydrolases and glycosyltransferases, frequently display a modular structure (Figs. 1 and2). In the genomic era, this modularity is of particular importance for correct open reading frame (ORF) annotation and functional prediction.!!...!!