Study on matrix additives for sensitive analysis of lipid A using MALDI mass spectrometry

摘要

The phosphorylation of lipid A plays a key role in bacterial pathogenicity, in which diphosphorylated species generally result in higher inflammatory properties of lipid A than their corresponding monophosphoryl forms. A newly developed vaccine against swine flu has activated the adjuvant debate and perhaps also highlighted the need for a sensitive analysis of the phosphorylation profiles of lipid A-based adjuvants. MALDI MS has been widely used for lipid A analysis, however, inconsistent patterns of phosphorylation have been produced using different matrix systems. We have demonstrated that a combination of CMBT and EDTA as a matrix for MALDI MS analysis of lipid A can profoundly improve the detection limit. Furthermore, tolerance to salts and detergent was also significantly increased. The analysis results for the chromatographically fractionated mono- and diphosphorylated fractions proved that the mono-phosphorylated species were not originated from the fragmentation of diphosphorylated forms. We believe that this highly sensitive method makes it possible to obtain consistent phosphorylation profiles of phospholipids thus allowing monitoring and direct comparison of data from different batches, mass spectrometers, and laboratories.