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. 2003 Nov;71(11):6426–6434. doi: 10.1128/IAI.71.11.6426-6434.2003

FIG. 4.

FIG. 4.

Linear negative-ion MALDI-MS spectrum of O-deacylated LOS from wild-type strain 7169. All ion values are represented as average (avg.) masses. In the high-mass region above m/z 2500, six deprotonated molecular ion species, (M-H)−, were identified at m/z 2633.2, 2756.4, 2795.3, 2879.6, 2918.5, and 3042.1. At lower mass levels, several prompt fragments were observed that were generated by cleavage at the labile KDO-lipid A glycosidic linkage yielding two oligosaccharide (OS) fragments at m/z 1737.1 and 1898.6 and three di-N-acyl lipid A (lipid A′) fragments at m/z 895.9, 1019.0, and 1142.5, respectively. The two OS fragments differed by the mass of a single hexose (Hex; ΔM = 162 Da) and the three lipid A′ species differed by the mass of one or two PEAs (ΔM = 123 Da). The heterogeneity of the OS (two isoforms) and lipid A′ (three isoforms) was consistent with the presence of the six LOS glycoforms differing in the total number of hexose residues (8 or 9) and/or the number of PEAs (0, 1, or 2) that modified one or more of the two phosphates (P) on lipid A′. The calculated average masses for the intact molecular ions and their OS and lipid A′ fragments are shown in the boxed inset structure.