Mapping and sequencing of cardiolipins from Geobacillus stearothermophilus NRS 2004/3a by positive and negative ion nanoESI-QTOF-MS and MS/MS

Analysis of glycosylated cardiolipins from thermophilic bacteria using GC-MS and LC-ESI-MS/MS methods

Unusual glucose-substituted cardiolipins (Glcx-CLs) in three genera of thermophilic bacteria, having more than one glycosidically linked glucose to the hydroxyl of the central glycerol of Glcx-CLs were identified for the first time in thermophilic bacteria of the genera Geobacillus, Meiothermus, and Thermus. The number of glucoses reached up to five units. The structure of glycosidically linked oligosaccharides was determined based on shotgun analysis MS (electrospray high-resolution tandem mass spectrometry), partially methylated alditol acetates were identified by GC-MS, both electron ionization (EI) and positive chemical ionization (PCI), hydrophilic interaction liquid chromatography (HILIC) separation and identification of CLs glycosides by high resolution MS-ESI, and digestion by specific glycosidases.

Hybrid 193 nm Ultraviolet Photodissociation Mass Spectrometry Localizes Cardiolipin Unsaturations

Developing alternative MS/MS strategies to distinguish isomeric lipids has become a high impact goal in shotgun lipidomics. Novel approaches have been developed to resolve structural features that are not discernible by traditional shotgun methods and have consequently promoted the discovery of new disease biomarkers. However, these methods have largely been limited to characterizing lipids with low structural complexity. Here, ultraviolet photodissociation (UVPD) strategies for phospholipid characterization are expanded for analysis of cardiolipins (CL), a class of phospholipids that exhibits a higher degree of structural complexity. A hybrid collision induced dissociation/193 nm UVPD (CID/UVPD) approach was implemented to pinpoint the location of both double bond and cyclopropyl unsaturations on the four acyl chains of CLs. This strategy was complemented with CID for the de novo elucidation of unknown CLs in biological extracts.

Greazy: Open-Source Software for Automated Phospholipid Tandem Mass Spectrometry Identification

Lipid identification from data produced with high-throughput technologies is essential to the elucidation of the roles played by lipids in cellular function and disease. Software tools for identifying lipids from tandem mass (MS/MS) spectra have been developed, but they are often costly or lack the sophistication of their proteomics counterparts. We have developed Greazy, an open source tool for the automated identification of phospholipids from MS/MS spectra, that utilizes methods similar to those developed for proteomics. From user-supplied parameters, Greazy builds a phospholipid search space and associated theoretical MS/MS spectra. Experimental spectra are scored against search space lipids with similar precursor masses using a peak score based on the hypergeometric distribution and an intensity score utilizing the percentage of total ion intensity residing in matching peaks. The LipidLama component filters the results via mixture modeling and density estimation. We assess Greazy's performance against the NIST 2014 metabolomics library, observing high accuracy in a search of multiple lipid classes. We compare Greazy/LipidLama against the commercial lipid identification software LipidSearch and show that the two platforms differ considerably in the sets of identified spectra while showing good agreement on those spectra identified by both. Lastly, we demonstrate the utility of Greazy/LipidLama with different instruments. We searched data from replicates of alveolar type 2 epithelial cells obtained with an Orbitrap and from human serum replicates generated on a quadrupole-time-of-flight (Q-TOF). These findings substantiate the application of proteomics derived methods to the identification of lipids. The software is available from the ProteoWizard repository: http://tiny.cc/bumbershoot-vc12-bin64 .

Electrospray ionization with low-energy collisionally activated dissociation tandem mass spectrometry of glycerophospholipids: mechanisms of fragmentation and structural characterization

This review describes the use of low-energy collisionally activated dissociation (CAD) with both tandem quadrupole and ion-trap mass spectrometry toward structural characterization of glycerophospholipids (GPLs), including classes of glycerophosphocholine, glycerophosphoethanolamine, glycerophosphoserine, glycerophosphoglycerol glycerophosphoinositol and glycerophosphatidic acid, as well as their lyso-, plasmanyl-, and plasmenylphospholipid subclasses. The mechanisms underlying the fragmentation processes leading to structural characterization of GPLs in various ion forms desorbed by electrospray ionization in the positive-ion and negative-ion modes are also discussed. The tandem mass spectrometric approaches afford the identification of the polar head group, the fatty acid substituents and the location of the radyl groups on the glycerol backbone of all the GPLs.

Mass spectrometry analysis of oxidized phospholipids

The evidence that oxidized phospholipids play a role in signaling, apoptotic events and in age-related diseases is responsible for the increasing interest for the study of this subject. Phospholipid changes induced by oxidative reactions yield a huge number of structurally different oxidation products which difficult their isolation and characterization. Mass spectrometry (MS), and tandem mass spectrometry (MS/MS) using the soft ionization methods (electrospray and matrix-assisted laser desorption ionization) is one of the finest approaches for the study of oxidized phospholipids. Product ions in tandem mass spectra of oxidized phospholipids, allow identifying changes in the fatty acyl chain and specific features such as presence of new functional groups in the molecule and their location along the fatty acyl chain. This review describes the work published on the use of mass spectrometry in identifying oxidized phospholipids from the different classes.

IR-MALDI-MS Analysis of HPTLC-Separated Phospholipid Mixtures Directly from the TLC Plate

The application of a recently developed direct coupling of high-performance thin-layer chromatography (HPTLC) and infrared matrix-assisted laser desorption/ionization orthogonal extracting time-of-flight mass spectrometry (Dreisewerd, K.; Müthing, J.; Rohlfing, A.; Meisen, I.; Vukelic, Z.; Peter-Katalinic, J.; Hillenkamp, F.; Berkenkamp, S. Anal. Chem. 2005, 77, 4098-4107) to the analysis of phospholipid mixtures is demonstrated. Mixtures of six phospholipid types were exemplarily analyzed. The sensitivity was found to be in the range between about 10 and 150 pmol of material spotted for HPTLC, depending on phospholipid acidity, Rf value, and ion polarity. The lateral resolution of the analysis is on the order of the laser focus diameter of about 220 x 300 microm2, allowing differentiation between phospholipid species of different acyl chain composition within one single HPTLC band, which were undistiguishable by a mere visual assessment. Analyte diffusion due to the addition of glycerol to the HPTLC plate was found to be-if at all notable-of only minor importance.

Characterization of cardiolipin as the sodiated ions by positive-ion electrospray ionization with multiple stage quadrupole ion-trap mass spectrometry

The application of multiple-stage ion-trap (IT) mass spectrometric methods for the structural characterization of cardiolipin (CL), a 1,3-bisphosphatidyl-sn-glycerol that consists of four fatty acyl chains and three glycerol backbones (designated as A, B, and central glycerol, respectively), as the sodiated adduct ions in the positive-ion mode was evaluated. Following collisionally activated dissociation (CAD), the [M - 2H + 3Na]+ ions of CL yield two prominent fragment ion pairs that consist of the phosphatidyl moieties attached to the 1'- and 3'-position of the central glycerol, respectively, resulting from the differential losses of the diacylglycerol moieties containing A and B glycerol, respectively. The results are consistent with those previously described for the [M - H]- and [M - 2H + Na]- ions in the negative-ion mode, thus permitting assignment of the two phosphatidyl moieties attached to the 1'- or 3'-position of the central glycerol. The identities of the fatty acyl substituents and their positions on the glycerol backbones (glycerol A and B) are deduced from further degradation of the above ion pairs that give the fragment ions reflecting the fatty acid substituents at the sn-1 (or sn-1') and sn-2 (or sn-2') positions. The ions that arise from losses of the fatty acid substituents at sn-1 and sn-1', respectively, are prominent, but the analogous ions from losses of the fatty acid substituents at sn-2 and sn-2', respectively, are of low abundance in the MS2 product-ion spectra. This feature further confirms the assignment of the positions of the fatty acid substituents. The similar IT multiple-stage mass spectrometric approaches including MS2 and MS3 for structural characterization of CL using its [M + Na]+ and the [M - H + 2Na]+ ions are also readily applicable. However, their uses for structural characterization are less desirable because formation of the [M + Na]+ and the [M - H + 2Na]+ ions for CL is not predictable.

Characterization of cardiolipin from Escherichia coli by electrospray ionization with multiple stage quadrupole ion-trap mass spectrometric analysis of [M - 2H + Na]- ions

We report a multiple-stage ion-trap (IT) mass spectrometric approach with electrospray ionization (ESI) for structural characterization of the [M - 2H + Na]- ion of cardiolipin (CL), a 1,3-bisphosphatidyl-sn-glycerol that consists of four fatty acyl chains and three glycerol backbones designated as A, B, and central glycerol, respectively (see Scheme 1). Following collisionally activated dissociation (CAD), the [M - 2H + Na]- ions of CL yield two prominent fragment ions that arise from the differential losses of the diacylglycerol moieties containing A or B glycerol, respectively. The tentative assignment of the two phosphatidyl moieties attached to the 1'- or 3'-position of the central glycerol is based on the observation that the ions arising from loss of the diacylglycerol moiety containing glycerol B is more abundant than that containing glycerol A. The structures of the above two ions, including the identities of the fatty acyl substituents and the position of fatty acyl substituents on the glycerol backbones (glycerol A and B) are determined by MS3 experiments that give spectra comprising several sets of prominent ions informative for the structural assignment of the fatty acyl substituents on the glycerol A and glycerol B. This method permits the structures of CL in a mixture isolated from Escherichia coli, including species that consist of various isomers, to be unveiled in detail.

Shotgun lipidomics: electrospray ionization mass spectrometric analysis and quantitation of cellular lipidomes directly from crude extracts of biological samples

Lipidomics, after genomics and proteomics, is a newly and rapidly expanding research field that studies cellular lipidomes and the organizational hierarchy of lipid and protein constituents mediating life processes. Lipidomics is greatly facilitated by recent advances in, and novel applications of, electrospray ionization mass spectrometry (ESI/MS). In this review, we will focus on the advances in ESI/MS, which have facilitated the development of shotgun lipidomics and the utility of intrasource separation as an enabling strategy for utilization of 2D mass spectrometry in shotgun lipidomics of biological samples. The principles and experimental details of the intrasource separation approach will be extensively discussed. Other ESI/MS approaches towards the quantitative analyses of global cellular lipidomes directly from crude lipid extracts of biological samples will also be reviewed and compared. Multiple examples of lipidomic analyses from crude lipid extracts employing these approaches will be given to show the power of ESI/MS techniques in lipidomics. Currently, modern society is plagued by the sequelae of lipid-related diseases. It is our hope that the integration of these advances in multiple disciplines will catalyze the development of lipidomics, and such development will lead to improvements in diagnostics and therapeutics, which will ultimately result in the extended longevity and an improved quality of life for humankind.

Structural characterization of cardiolipin by tandem quadrupole and multiple-stage quadrupole ion-trap mass spectrometry with electrospray ionization

We report negative-ion electrospray tandem mass spectrometric methods for structural characterization of cardiolipin (CL), a four-acyl-chain phospholipid containing two distinct phosphatidyl moieties, of which structural assignment of the fatty acid residues attached to the glycerol backbones performed by low-energy CAD tandem mass spectrometry has not been previously described. The low-energy MS2-spectra of the [M - H]- and [M - 2H]2- ions obtained with ion-trap or with tandem quadrupole instrument combined with ion-trap MS3-spectra or with source CAD product-ion spectra provide complete structural information for CL characterization. The MS2-spectra of the [M - H]- ions contain two sets of prominent fragment ions that comprise a phosphatidic acid, a dehydrated phosphatidylglycerol, and a (phosphatidic acid + 136) anion. The substantial differences in the abundances of the two distinct phosphatidic anions observed in the MS2-spectra of the [M -H]- ions lead to the assignment of the phosphatidyl moieties attached to the 1' or 3' position of central glycerol. Upon further collisional dissociation, the MS3-spectra of the phosphatidic anions provide information to identify the fatty acyl substituents and their position in the glycerol backbone. The MS2-spectra of the [M - 2H]2- ions obtained with TSQ or ITMS contain complementary information to confirm structural assignment. The applications of the above methods in the differentiation of cardiolipin isomers and in the identification of complex cardiolipin species consisting of multiple molecular structures are also demonstrated.

Capillary electrophoresis-mass spectrometry for glycoscreening in biomedical research

Application of capillary electrophoresis (CE) in combination with mass spectrometry (MS) and tandem MS to glycoscreening in biomedical projects is highlighted. In the first part recent CE-MS experiments by sheath liquid CE and multiple stage MS are reported. Neutral and negatively charged N-glycan mixtures from ribonuclease B and fetuin, high-mannose type N-glycoforms, oligosaccharides from lipopolysaccharides (LPS) of Haemophilus influenzae, polysaccharides of Pseudomonas aeruginosa and Staphylococcus aureus were analyzed. A particular emphasis is devoted to the applicability of novel off- and on-line CE-MS and tandem MS methods for screening of proteoglycan-derived oligosaccharides, glycosaminoglycans (GAGs), such as hyaluronates from Streptococcus agalactiae, chondroitin/dermatan sulfates (CS/DS) from bovine aorta and human skin fibroblast decorin, and heparin/heparan sulfate (HS) from porcine and bovine mucosa. The performance of CE-MS/MS for identification of glycoforms in glycopeptides and glycoproteins is illustrated by experiments performed on complex mixtures from urine of patients suffering from a hereditary N-acetylhexosaminidase deficiency (Schindler's disease) and urine of patients suffering from cancer cachexia. For determination of glycosylation patterns in glycoproteins like enzymes and antibodies by CE/MS, both CE-matrix assisted laser desorption/ionization (MALDI) and CE-electrospray ionization (ESI)-MS were functional. Finally, the potential of CE-ESI-MS strategy in glycolipid analysis is demonstrated for gangliosides from bovine brain for which particular CE buffer conditions are required.

Coupling of fully automated chip electrospray to Fourier transform ion cyclotron resonance mass spectrometry for high-performance glycoscreening and sequencing

The NanoMate robot has been coupled to a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer at 9.4 T and implemented for the first time for complex carbohydrate analysis. It was optimized in the negative ion mode to achieve automated sample delivery on the chip along with increased sensitivity, ultra-high resolution and accurate mass determination. A novel bracket has been designed to allow a reliable mounting of the NanoMate to the Apollo electrospray ionization (ESI) source of an APEX II instrument. The notably higher efficiency of ionization for compositional mapping of complex mixtures and feasibility for fragmentation analysis of components by sustained off-resonance irradiation collision-induced tandem mass spectrometry (SORI-CID MS2) has been demonstrated on a glycoconjugate mixture containing O-glycosylated sialylated peptides from urine of a patient suffering from a hereditary N-acetylhexosaminidase deficiency (Schindler's disease), previously analyzed by capillary-based nanoESI-FTICRMS, and of a healthy control person. Due to its potential to generate highly charged ionic species, reduce the in-source fragmentation, increase sensitivity, reproducibility and ionization efficiency, along with the ability to generate a sustained and constant electrospray, this method can be considered as a new platform for advanced glycomics.

Charting molecular composition of phosphatidylcholines by fatty acid scanning and ion trap MS3 fragmentation

The molecular composition of phosphatidylcholines (PCs) in total lipid extracts was characterized by a combination of multiple precursor ion scanning on a hybrid quadrupole time-of-flight mass spectrometer and MS3 fragmentation on an ion trap mass spectrometer. Precursor ion spectra for 50 acyl anion fragments of fatty acids (fatty acid scanning) acquired in parallel increased the specificity and the dynamic range of the detection of PCs and identified the fatty acid moieties in individual PC species. Subsequent analysis of detected PC peaks by MS3 fragmentation on an ion trap mass spectrometer quantified the relative amount of their positional isomers, thus providing the most detailed and comprehensive characterization of the molecular composition of the pool of PCs at the low-picomole level. The method is vastly simplified, compared with conventional approaches, and does not require preliminary separation of lipid classes or of individual molecular species, enzymatic digestion, or chemical derivatization. The approach was validated by the comparative analysis of the molecular composition of PCs from human red blood cells. In the total lipid extract of Madin-Darby canine kidney II cells, we detected 46 PC species with unique fatty acid composition and demonstrated that the presence of positional isomers almost doubled the total number of individual molecular species.

Electrospray mass spectrometry of phospholipids

Phospholipids play a central role in the biochemistry of all living cells. These molecules constitute the lipid bilayer defining the outer confines of a cell, but also serve as the structural entities which confine subcellular components. Mass spectrometry has emerged as a powerful tool useful for the qualitative and quantitative analysis of complex phospholipids, including glycerophospholipids and the sphingolipid, sphingomyelin. Collision induced decomposition of both positive and negative molecular ion species yield rich information as to the polar head group of the phospholipid and the fatty-acyl substituents esterified to the glycerophospholipid backbone. This review presents the current level of understanding of the mechanisms involved in the formation of various product ions following collisional activation of molecular ion species generated by electrospray ionization of the common glycerophospholipids, including phosphatidic acid, phosphatidylethanolamine, phosphatidylcholine, phosphatidylinositol, phosphatidylglycerol, phosphatidylserine, cardiolipin, and sphingomyelin. Recent advances in the application of matrix assisted laser desorption ionization is also considered. Several applications of mass spectrometry applied to phospholipid analysis are presented as they apply to physiology as well as pathophysiology.

Isolation of glucocardiolipins from Geobacillus stearothermophilus NRS 2004/3a

Glucose-substituted cardiolipins account for about 4 mol% of total phospholipid extracted from exponentially grown cells of Geobacillus stearothermophilus NRS 2004/3a. Individual glucocardiolipin species exhibited differences in fatty acid substitution, with iso-C(15:0) and anteiso-C(17:0) prevailing. The compounds were purified to homogeneity by a novel protocol and precharacterized by matrix-assisted laser desorption ionization time-of-flight mass spectrometry.