InterPro: IPR002201 Glycosyl transferase, family 9

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 (EC: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 [2]. 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 9 GT9 comprises enzymes with two known activity; lipopolysaccharide N-acetylglucosaminyltransferase (EC:2.4.1.56), heptosyltransferase (EC:2.4).

Heptosyltransferase I is thought to add L-glycero-D-manno-heptose to the inner 3-deoxy-D-manno-octulosonic acid (Kdo) residue of the lipopolysaccharide core [3]. Heptosyltransferase II is a glycosyltransferase involved in the synthesis of the inner core region of lipopolysaccharide [4]. Lipopolysaccharide is a major component of the outer leaflet of the outer membrane in Gram-negative bacteria. It is composed of three domains; lipid A, Core oligosaccharide and the O-antigen. These enzymes transfer heptose to the lipopolysaccharide core [3].