Fig. 4.
18O from 18O2 is incorporated into the outer Kdo unit of Kdo2-lipid A by KdoO. A and B. KdoO expressing cells grown with 18O2 generate a Kdo2-lipid A derivative that is 1 m/z larger (as a doubly-charged species) than seen with 16O2-grown cells (blue vs. yellow spectra, respectively), confirming the incorporation of an O2-derived oxygen atom into the product. The asterisk* indicates the presence of the sodium adduct [M-3H + Na] ion of Kdo2-lipid A. C, D, and E. ESI-MS/MS analysis of Kdo2-lipid A, Ko-Kdo-lipid A, and [18O]Ko-Kdo-lipid A shows that YpKdoO modifies the outer Kdo unit, as evidenced in E by the [M-H]- ion of [18O]Ko at m/z 255.073, the [M-H216O-H]-ion of [18O]Ko at m/z 237.062, and the absence of corresponding [16O]Kdo fragments. Schematic descriptions are the same as in Fig. 1, except that [18O]Ko is indicated with a blue box.