Structural characterization of complex bacterial glycolipids by Fourier transform mass spectrometry

Bacterial glycolipids are complex amphiphilic molecules which are on the one hand of utmost importance for the organization and function of bacterial membranes, and which on the other hand play a major role in the activation of cells of the innate and adaptive immune system of the host. Already small alterations of their chemical structure may influence the biological activity tremendously. Due to their intrinsic biological heterogeneity [number and type of fatty acids, saccharide structures, and substitution with e.g. phosphate (P), 2-aminoethyl- (pyro)phosphate groups (P-Etn) or 4-amino-4-deoxyarabinose (Ara4N)], separation of the different components are a prerequisite for unequivocal chemical and NMR structural analyses. In this contribution the structural information which can be obtained from heterogeneous samples of glycolipids by Fourier transform (FT) ion cyclotron resonance mass spectrometric methods is described. By means of recently analysed complex biological samples the possibilities of high resolution electrospray ionization FT-MS are demonstrated. Capillary skimmer dissociation, as well as tandem mass spectrometry MS/MS analysis utilizing collision-induced dissociation and infrared multiphoton dissociation, are compared and their advantages to provide structural information of diagnostic importance are discussed.