Crystallization and preliminary X-ray crystallographic studies of 3-deoxy-manno-octulosonate cytidylyltransferase from Haemophilus influenzae.

The enzyme 3-deoxy-manno-octulosonate cytidylyltransferase (CMP-KDO synthetase; CKS) catalyzes the activation of 3-deoxy-manno-octulosonate (KDO) by forming CMP-KDO. It is essential for the biosynthesis of lipopolysaccharides in Gram-negative bacteria and is a potential target for the discovery of antibacterial agents. L-CKS from Haemophilus influenzae was overexpressed with a C-terminal hexahistidine tag in Escherichia coli and crystallized in the presence of the substrate KDO at 297 K using PEG 4000 as a precipitant and ethylene glycol as an additive. The diffraction limit and spot shape of the native crystal could be improved significantly by dehydration/annealing. X-ray diffraction data were collected to 2.5 A resolution from a native crystal. The crystals are orthorhombic, belonging to the space group P2(1)2(1)2(1), with unit-cell parameters a = 48.6, b = 83.1, c = 117.3 A. The presence of two monomers of recombinant L-CKS in the crystallographic asymmetric unit gives a reasonable V(M) of 2.05 A(3) Da(-1), with a solvent content of 40.0%.