Structure of 3-deoxy-manno-octulosonate cytidylyltransferase from Haemophilus influenzae complexed with the substrate 3-deoxy-manno-octulosonate in the beta-configuration.

The enzyme 3-deoxy-manno-octulosonate cytidylyltransferase (CMP-KDO synthetase; CKS) catalyzes the activation of 3-deoxy-D-manno-octulosonate (or 2-keto-3-deoxy-manno-octonic acid; KDO) by forming CMP-KDO. CKS is unique to Gram-negative bacteria and is an attractive target for the development of antibacterial agents. The crystal structure of CKS from Haemophilus influenzae in complex with the substrate KDO has been determined at 2.30 A resolution by combining single-wavelength anomalous diffraction and molecular-replacement methods. The two monomers in the asymmetric unit differ in the conformation of their C-terminal alpha-helix (Ala230-Asn254). The KDO bound to the active site exists as the beta-pyranose form in the (5)C(2) chair conformation. The structure of CKS from H. influenzae in complex with KDO will be useful in structure-based inhibitor design.