Although the transcriptome, proteome, and interactome of several eukaryotic model organisms have been described in detail, lipidomes remain relatively uncharacterized. Using Saccharomyces cerevisiae as an example, we demonstrate that automated shotgun lipidomics analysis enabled lipidome-wide absolute quantification of individual molecular lipid species by streamlined processing of a single sample of only 2 million yeast cells. By comparative lipidomics, we achieved the absolute quantification of 250 molecular lipid species covering 21 major lipid classes. This analysis provided Ϸ95% coverage of the yeast lipidome achieved with 125-fold improvement in sensitivity compared with previous approaches. Comparative lipidomics demonstrated that growth temperature and defects in lipid biosynthesis induce ripple effects throughout the molecular composition of the yeast lipidome. This work serves as a resource for molecular characterization of eukaryotic lipidomes, and establishes shotgun lipidomics as a powerful platform for complementing biochemical studies and other systems-level approaches.fatty acid elongation ͉ S. cerevisiae ͉ shotgun lipidomics T he lipidome of eukaryotic cells consists of hundreds to thousands of individual lipid species that constitute membranes, store metabolic energy and function as bioactive molecules (1-3). Despite the extensive characterization of proteins, their association into complexes and activities (4-6), it is still difficult to assess how perturbations within the lipid metabolic network affect the full lipidome of cells. This work shows that lipidome-wide quantification of individual molecular lipid species (molecules with defined chemical structure) by absolute quantification (expressed in mol or mol%) provides a new approach to relate lipidomics and functional genomics studies.The yeast Saccharomyces cerevisiae serves as a prime model organism for studying the molecular organization and regulatory circuitry of eukaryotic lipidomes (7-9). It uses a relatively simple and conserved network of lipid metabolic pathways (Fig. 1) that synthesize a few hundred molecular lipid species constituting its full lipidome (3). The lipidome diversity is primarily determined by the fatty acid synthase (10), the ⌬-9 desaturase (11) and the fatty acid elongation complex (12) that produce only saturated or mono-unsaturated fatty acids having 10 to 26 carbon atoms for the biosynthesis of glycerolipids, glycerophospholipids, and sphingolipids. Importantly, several metabolic conversions interlink sphingolipid, glycerophospholipid, and glycerolipid metabolism such that any perturbation within the metabolic network is prone to induce lipidome-wide ripple effects. Remarkably, numerous genes involved in lipid metabolism and trafficking can be mutated or deleted without apparent physiological consequences (Fig. 1).Despite remarkable methodological advances, lipidomics seldom complements functional genomics efforts owing to three major factors. First, analysis of glycerophospholipids and sphingolipids requires ...

We report a method for the identification and quantification of glycerophospholipid molecular species that is based on the simultaneous automated acquisition and processing of 41 precursor ion spectra, specific for acyl anions of common fatty acids moieties and several lipid class-specific fragment ions. Absolute quantification of identified species was linear within a concentration range of 10 nM-100 microM and was achieved by spiking into total lipid extracts a set of synthetic lipid standards with diheptadecanoyl (17:0/17:0) fatty acid moieties, representing six common classes of glycerophospholipids. The automated analysis of total lipid extracts was powered by a robotic nanoflow ion source and produced currently the most detailed description of the glycerophospholipidome.

Comparisons between tears and meibum indicate that meibum is likely to supply the majority of lipids in the tear film lipid layer. However, the observed higher mole ratio of phospholipid in tears shows that analysis of meibum alone does not provide a complete understanding of the tear film lipid composition.

The analysis of lipids by mass spectrometry (MS) can provide in-depth characterization for many forms of biological samples. However, such workflows can also be hampered by challenges like low chromatographic resolution for lipid separations and the convolution of mass spectra from isomeric and isobaric species. To address these issues, we describe the use of differential mobility spectrometry (DMS) as a rapid and predictable separation technique within a shotgun lipidomics workflow, with a special focus on phospholipids (PLs). These analytes, ionized by electrospray ionization (ESI), are filtered using DMS prior to MS analysis. The observed separation (measured in terms of DMS compensation voltage) is affected by several factors, including the m/z of the lipid ion, the structure of an individual ion, and the presence of chemical modifiers in the DMS cell. Such DMS separations can simplify the analysis of complex extracts in a robust and reproducible manner, independent of utilized MS instrumentation. The predictable separation achieved with DMS can facilitate correct lipid assignments among many isobaric and isomeric species independent of the resolution settings of the MS analysis. This leads to highly comprehensive and quantitative lipidomic outputs through rapid profiling analyses, such as Q1 and MRM scans. The ultimate benefit of the DMS separation in this unique shotgun lipidomics workflow is its ability to separate many isobaric and isomeric lipids that by standard shotgun lipidomics workflows are difficult to assess precisely, for example, ether and diacyl species and phosphatidylcholine (PC) and sphingomyelin (SM) lipids.