Abstract

3-Deoxy-d-manno-octulosonate 8-phosphate (KDO8P) synthase and 3-deoxy-d-arabino-heptulosonate 7-phosphate (DAH7P) synthase are two enzymes that catalyse related reactions in two distinct biosynthetic pathways. KDO8P synthase is responsible for the formation of an essential component of the lipopolysaccharide in Gram-negative bacteria. DAH7P synthase catalyses the first step of the shikimate pathway to aromatic amino acids. Both enzymes have been identified as targets for drug design. We have used a combination of structural studies, substrate analogues and site-directed mutagenesis to probe small but significant differences in the active sites of these two enzymes. These studies have illuminated important mechanistic differences and have clarified the evolutionary relationship between these two enzymes. In addition, we have shown that the activity of the M. tuberculosis DAH7P synthase is regulated synergistically by a combination of two aromatic amino acids, demonstrating an unusual mechanism for the regulation of aromatic metabolism.