Systematic screening for novel lipids by shotgun lipidomics

A commonly accepted LIPID MAPS classification recognizes eight major lipid categories and over 550 classes, while new lipid classes are still being discovered by targeted biochemical approaches. Despite their compositional diversity, complex lipids such as glycerolipids, glycerophospholipids, saccharolipids, etc. are constructed from unique structural moieties, e.g., glycerol, fatty acids, choline, phosphate, and trehalose, that are linked by amide, ether, ester, or glycosidic bonds. This modular organization is also reflected in their MS/MS fragmentation pathways, such that common building blocks in different lipid classes tend to generate common fragments. We take advantage of this stereotyped fragmentation to systematically screen for new lipids sharing distant structural similarity to known lipid classes and have developed a discovery approach based on the computational querying of shotgun mass spectra by LipidXplorer software. We applied this concept for screening lipid extracts of C. elegans larvae at the dauer and L3 stages that represent alternative developmental programs executed in response to environmental challenges. The search, covering more than 1.5 million putative chemical compositions, identified a novel class of lyso-maradolipids specifically enriched in dauer larvae.