Turnover of lipids in Mycobacterium smegmatis CDC 46 and Mycobacterium phlei ATCC 354

Discovery of a glycerol 3-phosphate phosphatase reveals glycerophospholipid polar head recycling in Mycobacterium tuberculosis

Functional assignment of enzymes encoded by the Mycobacterium tuberculosis genome is largely incomplete despite recent advances in genomics and bioinformatics. Here, we applied an activity-based metabolomic profiling method to assign function to a unique phosphatase, Rv1692. In contrast to its annotation as a nucleotide phosphatase, metabolomic profiling and kinetic characterization indicate that Rv1692 is a D,L-glycerol 3-phosphate phosphatase. Crystal structures of Rv1692 reveal a unique architecture, a fusion of a predicted haloacid dehalogenase fold with a previously unidentified GCN5-related N-acetyltransferase region. Although not directly involved in acetyl transfer, or regulation of enzymatic activity in vitro, this GCN5-related N-acetyltransferase region is critical for the solubility of the phosphatase. Structural and biochemical analysis shows that the active site features are adapted for recognition of small polyol phosphates, and not nucleotide substrates. Functional assignment and metabolomic studies of M. tuberculosis lacking rv1692 demonstrate that Rv1692 is the final enzyme involved in glycerophospholipid recycling/catabolism, a pathway not previously described in M. tuberculosis.

The two-domain LysX protein of Mycobacterium tuberculosis is required for production of lysinylated phosphatidylglycerol and resistance to cationic antimicrobial peptides

The well-recognized phospholipids (PLs) of Mycobacterium tuberculosis (Mtb) include several acidic species such as phosphatidylglycerol (PG), cardiolipin, phosphatidylinositol and its mannoside derivatives, in addition to a single basic species, phosphatidylethanolamine. Here we demonstrate that an additional basic PL, lysinylated PG (L-PG), is a component of the PLs of Mtb H37Rv and that the lysX gene encoding the two-domain lysyl-transferase (mprF)-lysyl-tRNA synthetase (lysU) protein is responsible for L-PG production. The Mtb lysX mutant is sensitive to cationic antibiotics and peptides, shows increased association with lysosome-associated membrane protein-positive vesicles, and it exhibits altered membrane potential compared to wild type. A lysX complementing strain expressing the intact lysX gene, but not one expressing mprF alone, restored the production of L-PG and rescued the lysX mutant phenotypes, indicating that the expression of both proteins is required for LysX function. The lysX mutant also showed defective growth in mouse and guinea pig lungs and showed reduced pathology relative to wild type, indicating that LysX activity is required for full virulence. Together, our results suggest that LysX-mediated production of L-PG is necessary for the maintenance of optimal membrane integrity and for survival of the pathogen upon infection.

Turnover of phospholipids and glycerides of spheroplasts of Mycobacterium smegmatis ATCC 14468

The breakdown and renewal of phospholipids and glycerides from spheroplasts of Mycobacterium smegmatis ATCC 14468 were studied by means of pulse labelling techniques using 1-14C-palmitate. Most of the radioactivity incorporated into total lipids was recovered from phospholipids. Among the phospholipids studied, cardiolipin had the highest radioactivity and specific activity, suggesting its higher pool size as compared to other fractions. The appreciable loss of radioactivity for cardiolipin in pulse chase experiments within growing cells suggests its metabolically active and dynamic nature. Glycerides exhibited no appreciable turnover rates.

Biosynthesis of hexamannophosphoinositides in Mycobacterium smegmatis ATCC 607

The biosynthesis of hexamannophosphoinositides in Mycobacterium smegmatis ATCC 607 was examined using labelled tri- and tetraacylated dimannophosphoinositides (PIM2(-3)F and PIM2(-4)F) as precursors, by in vivo and in vitro incorporation. Tetraacylated dimannoside was metabolically more active as compared to triacylated dimannoside and seems to be the precursor for the synthesis of hexamannophosphoinositides.

Phospholipid metabolism in Mycobacterium smegmatis ATCC 607 grown at 37 degrees and 27 C degrees C

The rate of synthesis and degradation of phospholipids in Mycobacterium smegmatis ATCC 607, grown at 27 degrees C and 37 degrees C was studied incorporation of 32P into phospholipids and chase of radioactivity of the pulse-labelled phospholipids. A relatively low rate of synthesis and degradation of phospholipids in cells growth at 27 degrees C was observed as compared to those grown at 37 degrees C. Phosphatidylethanolamine (PE) had the maximum turnover at 37 degrees C. However, at 27 degrees C, cardiolipin (CL) showed a turnover rate higher than PE. Phosphatidylinositol mannosides (PIMs) were metabolically more active at 37 degrees C than at 27 degrees C. The differences in metabolic activity of the phospholipids at the two temperatures have been discussed.