Oligosaccharide profile of VexL reaction products. Oligosaccharide profile of VexL reaction products. Shown is a charge-deconvoluted QToF mass spectrum of Vi antigen oligosaccharides generated by VexL depolymerization. Ions correspond to polymers of O-acetylated HexNAcA residues, from two to seven residues in length (yellow box symbols), with a nonreducing terminal 4-deoxy-α-d-galact-4-enuronosyl residue (gray box). Species with nonstoichiometric O-acetylation [Δ42.010 atomic mass units (amu)] and/or water-loss (Δ18.010 amu) are indicated with red and green arrows, respectively. Sean D. Liston et al. PNAS 2018;115:21:E4870-E4879 ©2018 by National Academy of Sciences