TABLE 3.
Molecular weight analysis of O-deacylated LOS by electrospray MS for MA-1 and MA-1 galE
| N. meningitidis strain | LOS | Observed (calculated) mol wta | Relative abundanceb by MALDI (ESI) | Proposed compositionc |
|---|---|---|---|---|
| MA-1 | LOS B | 2,428.0 (2,428.22) | 50 (36) | Hex2-Hep2-GlcNAc-PEA1-Kdo2-lipid A |
| LOS B′ | 2,551.1 (2,551.27) | 100 (100) | Hex2-Hep2-GlcNAc-PEA2-Kdo2-lipid A* | |
| MA-1 galE | LOS A | 2,266.4 (2,266.07) | 32 (43) | Hex-Hep2-GlcNAc-PEA1-Kdo2-lipid A* |
| LOS A′ | 2,389.3 (2,389.12) | 100 (100) | Hex-Hep2-GlcNAc-PEA2-Kdo2-lipid A* | |
| LOS B | 2,427.8 (2,428.22) | 20d (13) | Hex2-Hep2-GlcNAc-PEA1-Kdo2-lipid A* | |
| LOS B′ | 2,551.7 (2,551.27) | 11 (12) | Hex2-Hep2-GlcNAc-PEA2-Kdo2-lipid A* |
All molecular weights for O-deacylated LOS are reported from the MALDI data as their average mass values based on singly deprotonated charged molecular ions, (M − H)−.
Expressed as a percentage; determined from peak heights of the singly charged molecular ions for MALDI and of the doubly and triply charged ions for ESI.
After O deacylation, the lipid A moiety is converted into diphosphoryl diacyl lipid A, containing two N-linked β-hydroxymyristic acid chains with an average Mr of 953.0.
In the MALDI spectrum, this glycoform peak partially overlaps the potassium adduct of the molecular ion for the more abundant glycoform LOS A′ resulting in overestimation of this LOS B glycoform.