Structural elucidation of phosphatidylcholines from tissue using electron induced dissociation

Abstract

Lipids are an important class of biomolecules that have many different biological functions. Accurately characterizing the chemical structures of lipids is critical to understanding their roles in biochemical pathways. These pathways can be regioisomerically selective and can produce specific sn-chain and double bond positional isomers, highlighting the significance of understanding isomeric content. Conventional tandem mass spectrometry methods, such as collision induced dissociation (CID), often provide incomplete structural information for lipids and metabolites. Alternative ion activation methods, such as electron induced dissociation (EID), can provide more extensive fragmentation, enabling more thorough structural characterizations. Herein, we have used EID to identify phosphatidylcholine (PC) lipids generated directly from tissue surfaces via matrix-assisted laser desorption/ionization (MALDI). EID has enabled the identification of the lipid fatty acyl substituents at the sn-1 and sn-2 positions of the glycerol backbone as well as the localization of carbon-carbon double bond positions in the fatty acyl chains. This has provided for the identification of sn and double-bond positional isomers in rat brain tissue. EID also enabled the relative quantification of isomeric content in mixtures of lipid isomers in an imaging mass spectrometry workflow.