3-Deoxy-D-manno-octulosonate 8-phosphate (KDO8P) synthase catalyzes the condensation of phosphoenolpyruvate (PEP) with arabinose 5-phosphate (A5P) to form KDO8P and inorganic phosphate. KDO8P is the phosphorylated precursor of 3-deoxy-D-manno-octulosonate, an essential sugar of the lipopolysaccharide of Gram-negative bacteria. The crystal structure of the Escherichia coli KDO8P synthase has been determined by multiple wavelength anomalous diffraction and the model has been refined to 2.4 Å

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... ctor, 19.9%; R-free, 23.9%). KDO8P synthase is a homotetramer in which each monomer has the fold of a (␤/␣) 8 barrel. On the basis of the features of the active site, PEP and A5P are predicted to bind with their phosphate moieties 13 Å apart such that KDO8P synthesis would proceed via a linear intermediate. A reaction similar to KDO8P synthesis, the condensation of phosphoenolpyruvate, and erythrose 4-phosphate to form 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAH7P), is catalyzed by DAH7P synthase. In the active site of DAH7P synthase the two substrates PEP and erythrose 4-phosphate appear to bind in a configuration similar to that proposed for PEP and A5P in the active site of KDO8P synthase. This observation suggests that KDO8P synthase and DAH7P synthase evolved from a common ancestor and that they adopt the same catalytic strategy. 2 The structure factor amplitudes of the native data set and the refined coordinates of KDO8P synthase have been deposited in the Protein Data Bank (entry 1D9E).