Applications of mass spectrometry to lipids and membranes - PubMed (original) (raw)

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Applications of mass spectrometry to lipids and membranes

Richard Harkewicz et al. Annu Rev Biochem. 2011.

Abstract

Lipidomics, a major part of metabolomics, constitutes the detailed analysis and global characterization, both spatial and temporal, of the structure and function of lipids (the lipidome) within a living system. As with proteomics, mass spectrometry has earned a central analytical role in lipidomics, and this role will continue to grow with technological developments. Currently, there exist two mass spectrometry-based lipidomics approaches, one based on a division of lipids into categories and classes prior to analysis, the "comprehensive lipidomics analysis by separation simplification" (CLASS), and the other in which all lipid species are analyzed together without prior separation, shotgun. In exploring the lipidome of various living systems, novel lipids are being discovered, and mass spectrometry is helping characterize their chemical structure. Deuterium exchange mass spectrometry (DXMS) is being used to investigate the association of lipids and membranes with proteins and enzymes, and imaging mass spectrometry (IMS) is being applied to the in situ analysis of lipids in tissues.

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Figures

Figure 1

Figure 1

Examples of each of the eight categories of lipids as defined by the Lipid Metabolites and Pathways Strategy (LIPID MAPS) Consortium.

Figure 2

Figure 2

Flow chart depicting the lipid sample preparation and analysis protocol. After extraction, the

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omprehensive

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ipidomics

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nalysis by

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eparation

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implification (CLASS) or shotgun lipidomics approach is carried out. GC, gas chromatography; LC, liquid chromatography.

Figure 3

Figure 3

Various modes of tandem mass spectrometric analyses available on the triple quadrupole instrument. Reprinted with permission from Reference .

Figure 4

Figure 4

Examples of shotgun lipidomics. (a) Demonstration of intrasource separation, which is used to minimize ion suppression and improve detection of low-level species. Reprinted with permission from Reference . (b) Comparison of the lipid composition of yeast cells for wild-type (BY4741) cells versus those with a fatty acid elongase gene mutation (elo1Δ, elo2Δ, elo3Δ. Reprinted with permission from Reference .

Figure 5

Figure 5

Example of a comprehensive lipidomics analysis by separation simplification (CLASS) approach. A heat map shows the temporal changes of various lipid metabolites (prostaglandins), as well as gene expression, in endotoxin-stimulated mouse macrophage cells. Enzymes are shown in red font and the prostaglandin lipid metabolites are shown in blue font. The arrows depict the synthesis pathways, including various metabolite intermediates and corresponding enzymes. Changes are represented as a function of time (left to right), where rectangles indicate mRNA levels and circles indicate lipid metabolite levels. Greater intensity of red indicates increasing levels; greater intensity of green indicates decreasing levels; and gray represents no change in levels relative to unstimulated cells. When enzyme activity can result from multiple genes, each is represented as a separate line. Redrawn and reprinted with permission from Reference .

Figure 6

Figure 6

Examples of a few of the novel species observed recently in untargeted lipidomics mass spectrometry-based assays. References , , -, .

Figure 7

Figure 7

Example of the

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iverse

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sotope

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etabolic

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rofiling of

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abeled

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xogenous

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ubstrates using

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ass

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pectrometry (DIMPLES/MS) approach. (a) The characteristic doublet pattern, the observation of prostaglandin D2 (PGD2), and deuterium-labeled PGD2 produced by macrophage cells supplemented with deuterium-labeled arachidonic acid (AA-d8). (b) The unexpected observation of 22-carbon dihomo-prostaglandin D2 (dih-PGD2), resulting from the 2-carbon elongation of arachidonic acid (AA). Redrawn and reprinted with permission from Reference . amu, atomic mass unit; COX, cyclooxygenase; m/z, mass-to-charge ratio.

Figure 8

Figure 8

Deuterium exchange mass spectrometry (DXMS) used to investigate protein/enzyme associations with lipids. (a) Hydrogen atoms contained on a protein molecule can be divided into three classes based on their rate of exchange with the aqueous solvent. Those attached directly to carbon atoms (blue) hardly ever exchange; those attached to amino acid side chain atoms, the N-terminal amine, and the C-terminal carboxylic acid (green) exchange extremely rapidly; and amide hydrogen atoms (red) have variable exchange rates from seconds to months depending on the protein conformation and solvent accessibility. (b) Depictions of the membrane interactions for representatives of the three main kinds of phospholipase A2 (PLA2), (i) the small secreted sPLA2 (reprinted with permission from Reference 59), (ii) the cytosolic cPLA (reprinted with permission from Reference 60), and (iii) the calcium-independent iPLA2 (reprinted with permission from Reference 61). Each has a different and distinct interaction with the phospholipid membrane.

Figure 9

Figure 9

Examples of matrix-assisted laser desorption ionization imaging mass spectrometry used to investigate lipids in tissue samples. (a) Extracted ion image for m/z = 772.5 from a mouse brain slice. The mass of 772.5 Da corresponds to the 16:0/16:0-PC + K+ (potassium cation adduct) species. (b) Images from a section of mouse kidney. Using MS/MS scan mode and high mass accuracy to confirm identity, cholesterol (i), 16:0/18:2-PC (ii), 40:6-PC (iii), and 16:0/20:4/18:1-TAG (iv) were some of the lipid species observed. Panels a and b reprinted with permission from Reference . (c) Example of an ion mobility-mass spectrometry (IM-MS) two-dimensional plot for a nominally isobaric peptide (RPPGGFSP) and lipid (32:4-PC). The mass-to-charge ratio (m/z) is plotted on the x-axis, and ion mobility drift time is plotted on the y-axis. The mass-to-charge ratio signals overlap and cannot be resolved; however, they clearly have different ion mobility drift times. Reprinted with permission from Reference .

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