3-Deoxy-D-manno-octulosonate 8-phosphate (KDO8P) synthase catalyzes the con
densation of phosphoenolpyruvate (PEP) with arabinose B-phosphate (A5P) to
form KDO8P and inorganic phosphate, KDO8P is the phosphorylated precursor o
f 3-deoxy-D-manno-octulosonate, an essential sugar of the lipopolysaccharid
e of Gram-negative bacteria. The crystal structure of the Escherichia coli
KDO8P synthase has been determined by multiple wavelength anomalous diffrac
tion and the model has been refined to 2.4 Angstrom (R-factor, 19.9%; R-fre
e, 23.9%). KDO8P synthase is a homotetramer in which each monomer has the f
old of a (beta/alpha)(8) barrel. On the basis of the features of the active
site, PEP and A5P are predicted to bind with their phosphate moieties 13 A
ngstrom apart such that KDO8P synthesis would proceed via a linear intermed
iate. A reaction similar to KDO8P synthesis, the condensation of phosphoeno
lpyruvate, and erythrose 4-phosphate to form 3-deoxy-D-arabino-heptulosonat
e 7-phosphate (DAH7P), is catalyzed by DAH7P synthase, In the active site o
f 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 ac
tive site of KDO8P synthase, This observation suggests that KDO8P synthase
and DAH7P synthase evolved from a common ancestor and that they adopt the s
ame catalytic strategy.