Glycosyl transferase, family 3, subgroup, N-terminal <p>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 (<db_xref db="EC" dbkey="2.4.1.-"/>) and related proteins into distinct sequence based families has been described [<cite idref="PUB00009409"/>]. 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'.</p><p>The glycosyl transferase family includes anthranilate phosphoribosyltransferase (TrpD, <db_xref db="EC" dbkey="2.4.2.18"/>) and thymidine phosphorylase (<db_xref db="EC" dbkey="2.4.2.2"/>). All these proteins can transfer a phosphorylated ribose substrate. Thymidine phosphorylase (<db_xref db="EC" dbkey="2.4.2.2"/>) catalyses the reversible phosphorolysis of thymidine, deoxyuridine and their analogues to their respective bases and 2-deoxyribose 1-phosphate. This enzyme regulates the availability of thymidine and is therefore essential to nucleic acid metabolism.</p><p>This N-terminal domain is found in various family 3 glycosyl transferases, including anthranilate phosphoribosyltransferase (TrpD, <db_xref db="EC" dbkey="2.4.2.18"/>) and thymidine phosphorylase (<db_xref db="EC" dbkey="2.4.2.2"/>). All these proteins can transfer a phosphorylated ribose substrate. Thymidine phosphorylase catalyses the reversible phosphorolysis of thymidine, deoxyuridine and their analogues to their respective bases and 2-deoxyribose 1-phosphate. This enzyme regulates the availability of thymidine and is therefore essential to nucleic acid metabolism.</p>