Lipopolysaccharide heptosyltransferase is involved in the biosynthesis of lipooligosaccharide (LOS). Lipopolysaccharide (LPS) is a major component of the outer membrane of gram-negative bacteria. LPS heptosyltransferase transfers heptose molecules from ADP-heptose to 3-deoxy-D-manno-octulosonic acid (KDO), a part of the inner core component of LPS. This family belongs to the GT-B structural superfamily of glycoslytransferases, which have characteristic N- and C-terminal domains each containing a typical Rossmann fold. The two domains have high structural homology despite minimal sequence homology. The large cleft that separates the two domains includes the catalytic center and permits a high degree of flexibility.