Isolation and Characterization of Lipid A from GMMA

Lipid A was precipitated from GMMA as previously described [25 (link)] using mild acid hydrolysis with 1% acetic acid for 2 h at 100°C. Samples were centrifuged at 14,000 g for 15 min, the pellets resuspended in water, and washed twice with water. The pellets were dried overnight using a Speedvac, resuspended in chloroform-methanol 4:1, and mixed with an equal volume of Super DHB (Sigma-Aldrich) solution in water/acetonitrile 1:1 (vol/vol). Two μL of the mixture were loaded to the target plate (MTP 384 target plate ground steel BC, Bruker Daltonics) and analyzed by Ultraflex MALDI-TOF (Bruker Daltonics) in reflectron ion-negative mode. A Peptide Calibration Standard (Bruker Daltonics), mixed with the Super DHB solution, was included in each analysis. The m/z rations were determined by Flex Analysis software in comparison to the Peptide Standard.