OpsX from Haemophilus influenzae represents a novel type of heptosyltransferase I in lipopolysaccharide biosynthesis.

The inner core region of the lipopolysaccharide (LPS) of Haemophilus influenzae is characterized by the presence of a phosphorylated 3-deoxy-alpha-D-manno-octulosonic acid (Kdo). In this study, we show that the heptosyltransferase I adding the first L-glycero-D-manno-heptose residue to this acceptor is encoded by the gene opsX, which differs in substrate specificity from the other heptosyltransferase I, known as WaaC.