Lipidomic discovery of deoxysiderophores reveals a revised mycobactin biosynthesis pathway in Mycobacterium tuberculosis.

To measure molecular changes underlying pathogen adaptation, we generated a searchable dataset of more than 12,000 mass spectrometry events, corresponding to lipids and small molecules that constitute a lipidome for Mycobacterium tuberculosis. Iron is essential for M. tuberculosis survival, and the organism imports this metal using mycobactin and carboxymycobactin siderophores. Detection of an unexpected siderophore variant and deletions of genes for iron scavenging has led to a revised mycobactin biosynthesis model. An organism-wide search of the M. tuberculosis database for hypothetical compounds predicted by this model led to the discovery of two families of previously unknown lipids, designated monodeoxymycobactins and monodeoxycarboxymycobactins. These molecules suggest a revised biosynthetic model that alters the substrates and order of action of enzymes through the mycobactin biosynthetic pathway. We tested this model genetically by solving M. tuberculosis lipidomes after deletion of the iron-dependent regulator (ideR), mycobactin synthase B (mbtB), or mycobactin synthase G (mbtG). These studies show that deoxymycobactins are actively regulated during iron starvation, and also define essential roles of MbtG in converting deoxymycobactins to mycobactin and in promoting M. tuberculosis growth. Thus, lipidomics is an efficient discovery tool that informs genetic relationships, leading to a revised general model for the biosynthesis of these virulence-conferring siderophores.

A comparative lipidomics platform for chemotaxonomic analysis of Mycobacterium tuberculosis.

The lipidic envelope of Mycobacterium tuberculosis promotes virulence in many ways, so we developed a lipidomics platform for a broad survey of cell walls. Here we report two new databases (MycoMass, MycoMap), 30 lipid fine maps, and mass spectrometry datasets that comprise a static lipidome. Further, by rapidly regenerating lipidomic datasets during biological processes, comparative lipidomics provides statistically valid, organism-wide comparisons that broadly assess lipid changes during infection or among clinical strains of mycobacteria. Using stringent data filters, we tracked more than 5,000 molecular features in parallel with few or no false-positive molecular discoveries. The low error rates allowed chemotaxonomic analyses of mycobacteria, which describe the extent of chemical change in each strain and identified particular strain-specific molecules for use as biomarkers.

Loss of the acyl-CoA binding protein (Acbp) results in fatty acid metabolism abnormalities in mouse hair and skin.

Proper fatty acid metabolism is critical for hair and skin development and maintenance. The acyl-CoA binding protein (Acbp) is a widely expressed protein that binds long-chain fatty acyl-CoA esters and plays a role in fatty acyl-CoA transport and pool formation. However, loss of function of Acbp in the whole animal has not been investigated. Here, we show that deletion of Acbp in mouse results in sebocyte hyperplasia and sparse, matted hair with a greasy appearance. Consistent with these gross abnormalities, Acbp is highly expressed in the pilosebaceous units of mouse skin as determined by Northern analysis and in situ hybridization. Loss of Acbp also results in fatty acid metabolism abnormalities, with hair lipid profiles showing altered levels of triacylglycerols and nearly co-migrating lipids. These data suggest that Acbp plays a role in triacylglycerol biosynthesis, and that regulation of this process is important for proper hair and skin development and maintenance in the mouse.