InterPro domain: IPR001830

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 ([intenz: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'.

Glycosyltransferase family 20 GT20 comprises enzymes with only one known activity; alpha, alpha-trehalose-phosphate synthase [UDP-forming] ( 2.4.1.15 ).

Synthesis of trehalose in the yeast Saccharomyces cerevisiae is catalysed by the trehalose-6-phosphate (Tre6P) synthase/phosphatase complex, which is composed of at least three different subunits encoded by the genes TPS1, TPS2, and TSL1. Tps1 and Tps2 carry the catalytic activities of trehalose synthesis, namely Tre6P synthase (Tps1) and Tre6P phosphatase (Tps2), while TsI1 has regulatory functions. There is some evidence that TsI1 and Tps3 may share a common function with respect to regulation and/or structural stabilisation of the Tre6P synthase/phosphatase complex in exponentially growing, heat-shocked cells [ 2 ].

OtsA (trehalose-6-phosphate synthase) from Escherichia coli has homology to the full-length TPS1, the N-terminal part of TPS2 and an internal region of TPS3 (TSL1) of yeast [ 3 ].

1. A classification of nucleotide-diphospho-sugar glycosyltransferases based on amino acid sequence similarities. Biochem. J. 326 ( Pt 3), 929-39
2. Structural analysis of the subunits of the trehalose-6-phosphate synthase/phosphatase complex in Saccharomyces cerevisiae and their function during heat shock. Mol. Microbiol. 24, 687-95
3. Analysis of the otsBA operon for osmoregulatory trehalose synthesis in Escherichia coli and homology of the OtsA and OtsB proteins to the yeast trehalose-6-phosphate synthase/phosphatase complex. Gene 145, 9-15