Advanced Structural and Spatial Analysis of Lipids Using Ion Mobility-Mass Spectrometry
Ion mobility-mass spectrometry (IM-MS) provides rapid (μs-ms) two dimensional separations on the basis of molecular structure and mass-to-charge (m/z), respectively. Based on differences in intramolecular packing of various biomolecules, the added separation dimension allows resolution of isobaric (i.e., same m/z) or nearly isobaric lipids, peptides, carbohydrates, and oligonucleotides. Experimentally determined IM collision cross sections (i.e., apparent surface areas in squared Å) of major membrane lipid classes are interpreted by performing molecular dynamics simulations. Glycerophospholipid and sphingolipid signals are resolved by IM-MS based on structural differences of the glycerol and sphingosine backbones. In addition to resolving lipids from other biomolecules and classes of lipids, IM-MS is shown to be a useful method for mobility separation of exogenous chemical noise in support of relative quantitation of lipid changes in the Drosophila eas mutant. The advantages of IM-MS can be applied to spatially resolved imaging of lipid species in tissues and cells. Laser shaping and focusing based on digital light patterning for high spatial resolution studies of lipids, compatible with the IM-MS instrumental platform, is described.