The biosynthesis of disaccharides, oligosaccharides and polysaccharides involves the action of hundreds of different glycosyltransferases. These enzymes catalyse the transfer of sugar moieties from activated donor molecules to specific acceptor molecules, forming glycosidic bonds. A classification of glycosyltransferases using nucleotide diphospho-sugar, nucleotide monophospho-sugar and sugar phosphates (2.4.1.-) and related proteins into distinct sequence based families has been described [1]. This classification is available on the CAZy (CArbohydrate-Active EnZymes) web site. The same three-dimensional fold is expected to occur within each of the families. Because 3-D structures are better conserved than sequences, several of the families defined on the basis of sequence similarities may have similar 3-D structures and therefore form 'clans'.

The six-hairpin glycoside transferase domain contains up to seven alpha-hairpins arranged in closed circular array. Protein families that contain domains with this structure include glucoamylases, various endocellulases and exocellulases (catalytic domain), N-acyl-D-glucosamine 2-epimerases, bacterial maltose phosphorylase (central domain), and bacterial glucoamylases (C-terminal domain).

1. A classification of nucleotide-diphospho-sugar glycosyltransferases based on amino acid sequence similarities. Biochem. J. 326 ( Pt 3), 929-39

The biosynthesis of disaccharides, oligosaccharides and polysaccharides involves the action of hu
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