Lipidomics reveals control of Mycobacterium tuberculosis virulence lipids via metabolic coupling

Abstract

Mycobacterium tuberculosis synthesizes specific polyketide lipids that interact with the host and are required for virulence. Using a mass spectrometric approach to simultaneously monitor hundreds of lipids, we discovered that the size and abundance of two lipid virulence factors, phthiocerol dimycocerosate (PDIM) and sulfolipid-1 (SL-1), are controlled by the availability of a common precursor, methyl malonyl CoA (MMCoA). Consistent with this view, increased levels of MMCoA led to increased abundance and mass of both PDIM and SL-1. Furthermore, perturbation of MMCoA metabolism attenuated pathogen replication in mice. Importantly, we detected increased PDIM synthesis in bacteria growing within host tissues and in bacteria grown in culture on odd-chain fatty acids. Because M. tuberculosis catabolizes host lipids to grow during infection, we propose that growth of M. tuberculosis on fatty acids in vivo leads to increased flux of MMCoA through lipid biosynthetic pathways, resulting in increased virulence lipid synthesis. Our results suggest that the shift to host lipid catabolism during infection allows for increased virulence lipid anabolism by the bacterium.lipid virulence factor ͉ metabolic flux ͉ pathogenesis ͉ PDIM ͉ sulfolipid-1

Dealing with the unknown: Metabolomics and Metabolite Atlases

“…Stable isotopic label incorporation or chemical derivatization can also aid in structural confirmation based on mass shifts in specific fragments, though this approach is not viable for many experimental situations (i.e., clinical samples) [2,43]. For example, if it is postulated that a metabolite contains a nitrogen, comparison of the metabolite from 14 N versus 15 N cultures can confirm the number of nitrogen atoms per molecule and link them to specific MS/MS fragments. It can also be useful to globally compare isotopically labeled and unlabeled metabolite pools [44 -46].…”

“…EI is typically coupled to gas chromatography (GC/MS), and ESI is often coupled to liquid chromatography (LC/MS) or capillary electrophoresis (CE-MS) to resolve complex mixtures. Though it should be noted that Fourier transform ion cyclotron resonance mass spectrometry (FTICR/MS) can often resolve complex mixtures of metabolites without chromatography [15]. The wide range of chromatography (LC) options allow physical separation of most molecules to reduce signal suppression [16].…”

“…It can also be useful to globally compare isotopically labeled and unlabeled metabolite pools [44 -46]. Mass shifts between labeled and unlabeled metabolites ( 13 C-labeled, 15 N-labeled, and unlabeled samples) can be used to derive empirical formulas. This can also help differentiate metabolites from background ions (e.g., no chemical shift suggests a background ion).…”

High Accuracy Mass Measurement Approach in the Identification of Phospholipids in Lipid Extracts: 7 T Fourier-transform Mass Spectrometry and MS/MS Validation

“…4,[10][11][12][13][14][15][16][17] Even with the disadvantage of relatively low sensitivity, the direct-infusion ESI-FTMS approach is very easy to implement and also provides a good method to compare the global lipid distributions of two total lipid extracts under inspection.…”

“…[5][6][7][8] Indeed, a number of groups have shown that FTMS is a very effective tool in lipid analysis. [9][10][11][12][13][14] For example, Ivanova et al successfully utilized direct infusion electrospray ionization (ESI) FTMS to monitor the changes in the glycerophospholipid compositions of total lipid extracts obtained from intact and permeabilized RBL-2H3 (mucosal mast cell line) cells. 9 More recently, Taguchi and coworkers reported that ESI-FTMS coupled with liquid chromatography (LC) was useful in identifying the phospholipid molecular species of Caenorhabditis elegans.…”