FIGURE 1.

Determination of the topology of LptC. A, the graphic indicates the predicted OGM accessibility of cysteine derivatives of LptC under three experimental conditions. B, the fluorescent proteins generated under the three conditions were separated by SDS-PAGE and are shown. C, to verify equal expression and loading for each of the tested LptC constructs, the same gel was stained with SimplyBlue SafeStain. The arrow to the right of B and C indicates the migration of LptC. In condition 1, exposed Cys residues in intact cells were labeled by OGM before a quenching by β-mercaptoethanol and preparation of membrane ghosts. In condition 2, exposed Cys residues were blocked by preincubation with MTSET, which was removed prior to preparation of membrane ghosts and OGM labeling of newly exposed Cys residues. In condition 3, membrane ghosts were labeled directly with OGM.