MS analysis of intact PilE from N. gonorrhoeae strains grown in defined, choline-free medium. (A) Wt (N400) grown on solid conventional medium. (B) Wt (N400) grown on solid defined, choline-free medium. (C) pilE(S68A) (GE68) grown on solid defined, choline-free medium. The species labeled as bearing PE/PC modifications also carry the hexose-2,4-diacetamido-2,4,6-trideoxyhexose dissacharide (HexDATDH) in its acetylated (ac) form. The peaks in the MS spectra that are not labeled are listed in Table S3 in the supplemental material.