Fig. 1.

A proposed Kdo dioxygenase that generates the Ko moiety of B. ambifaria and Y. pestis LPS. A. A possible Fe²⁺/α-ketoglutarate/O₂-dependent dioxygenase, designated KdoO, might account for the origin of the Ko unit after Kdo₂-lipid A formation, consistent with the fact that Ko-containing bacteria make CMP-Kdo and transfer two Kdo residues to lipid A in the same manner as bacteria lacking Ko (15). LpxO, which generates the secondary S-2-hydroxymyristate substituent of Salmonella lipid A, provides a precedent for an analogous Kdo₂-lipid A hydroxylation (17). B. The bamb_0774 gene, located between waaC and waaA on the B. ambifaria chromosome [Copeland A, et al. (2006) Complete sequence of chromosomes 1, 2, and 3 and plasmid 1 of Burkholderia cenocepacia AMMD, submitted August 2006 to the European Molecular Biology Laboratory/GenBank/DNA Data Base in Japan databases] (35), was identified as a possible structural gene for the Kdo hydroxylase because it encodes a protein with the active site signature of a Fe²⁺/α-ketoglutarate/O₂-dependent dioxygenase (18). KdoO otherwise displays no sequence similarity to LpxO. C. Alignment of Bamb_0774 from B. ambifaria and Y1812 from Y. pestis KIM. These proteins share 52% identity (shown in red) and 64% similarity, and both contain the potential iron-binding motif, HXDX_nH (n > 40) (potential downstream His residues shown in blue). Schematic representations: Kdo, black boxes; Ko, orange box; glucosamine, blue ovals; acyl chains, green squiggles; phosphate group, P.