FIG 3.

Examination of the lipopolysaccharide core structures of O-antigen mutants by staining of carbohydrates and negative-ion multistage MALDI-MS. (A) Consistent with previously published data (58–60), the bands in the purified LPS lane shown in the PAGE gel and stained by emerald green are labeled lipid A–core–O-antigen (one unit), lipid A-core (no O-antigen subunit), and lipid A and are indicated by black arrows. (B) MALDI-MS analysis of O-LPS derived from the LVS 0708 mutant. MSⁿ analyses were performed to sequentially determine the components of the O-LPS. (C) MS/MS analysis of the precursor ion observed at m/z 1,747. (D) Subsequent MS³ analysis performed on the fragment ion observed at m/z 1,527. Peaks marked with asterisks designate major masses minus water or CO₂. (E) Completed core structure for LVS 0708::TrgTn (predicted for the Schu S4 1236::TrgTn strain as well) and predicted structure for LVS 0706::TrgTn (as well as the Schu S4 1238::TrgTn strain).