Cloning, expression, purification and preliminary crystallographic data for Rv3214 (EntD), a predicted cofactor-dependent phosphoglycerate mutase from Mycobacterium tuberculosis

Two enzymes with redundant fructose bisphosphatase activity sustain gluconeogenesis and virulence in Mycobacterium tuberculosis

The human pathogen Mycobacterium tuberculosis (Mtb) likely utilizes host fatty acids as a carbon source during infection. Gluconeogenesis is essential for the conversion of fatty acids into biomass. A rate-limiting step in gluconeogenesis is the conversion of fructose 1,6-bisphosphate to fructose 6-phosphate by a fructose bisphosphatase (FBPase). The Mtb genome contains only one annotated FBPase gene, glpX. Here we show that, unexpectedly, an Mtb mutant lacking GLPX grows on gluconeogenic carbon sources and has detectable FBPase activity. We demonstrate that the Mtb genome encodes an alternative FBPase (GPM2, Rv3214) that can maintain gluconeogenesis in the absence of GLPX. Consequently, deletion of both GLPX and GPM2 is required for disruption of gluconeogenesis and attenuation of Mtb in a mouse model of infection. Our work affirms a role for gluconeogenesis in Mtb virulence and reveals previously unidentified metabolic redundancy at the FBPase-catalysed reaction step of the pathway.

Mycobacterium tuberculosis feeds on host fatty acids during infection, a process that requires a fructose bisphosphatase (FBPase) enzyme for gluconeogenesis. Here, Ganapathy et al. show that the bacterium has two different FBPases and that this enzymatic activity is required for full virulence.

Phosphoproteomic analysis of bacillus Calmette-Guérin using gel-based and gel-free approaches

Post-translational modifications regulate many aspects of protein behavior and provide options for expanding protein functionality in organisms. Protein phosphorylation is one of the major PTMs observed in bacteria, which are involved in regulating a myriad of physiological processes. Mycobacterium bovis bacillus Calmette-Guérin (BCG) has been recognized as an important weapon in the fight against tuberculosis (TB) worldwide for over 80 years. In this study, we conducted phosphoproteomic analysis in BCG bacteria using gel-based and gel-free complementary approaches and high-resolution Fourier transform mass spectrometry. In total, 501 phosphopeptides derived from 398 phosphoproteins were identified, representing the first phosphoproteomic analysis of BCG reported to date. Thirty-three novel protein products supported by 36 unique phosphorylated peptides were detected. Additionally, the translational start sites of 28 proteins were confirmed, and 31 proteins were validated through the extension of translational start sites based on N-terminus-derived peptides. The expression of three randomly selected phosphoproteins was validated through Western blotting. A number of proteins involved in metabolic pathways, including glycolysis, the tricarboxylic acid cycle, oxidative phosphorylation and two-component system, are discussed. We believe some of the proteins identified in this study may represent potential targets for the development of novel antibiotics for treating TB.

Structural and functional analysis of Rv3214 from Mycobacterium tuberculosis, a protein with conflicting functional annotations, leads to its characterization as a phosphatase

The availability of complete genome sequences has highlighted the problems of functional annotation of the many gene products that have only limited sequence similarity with proteins of known function. The predicted protein encoded by open reading frame Rv3214 from the Mycobacterium tuberculosis H37Rv genome was originally annotated as EntD through sequence similarity with the Escherichia coli EntD, a 4'-phosphopantetheinyl transferase implicated in siderophore biosynthesis. An alternative annotation, based on slightly higher sequence identity, grouped Rv3214 with proteins of the cofactor-dependent phosphoglycerate mutase (dPGM) family. The crystal structure of this protein has been solved by single-wavelength anomalous dispersion methods and refined at 2.07-Angstroms resolution (R = 0.229; R(free) = 0.245). The protein is dimeric, with a monomer fold corresponding to the classical dPGM alpha/beta structure, albeit with some variations. Closer comparisons of structure and sequence indicate that it most closely corresponds with a broad-spectrum phosphatase subfamily within the dPGM superfamily. This functional annotation has been confirmed by biochemical assays which show negligible mutase activity but acid phosphatase activity with a pH optimum of 5.4 and suggests that Rv3214 may be important for mycobacterial phosphate metabolism in vivo. Despite its weak sequence similarity with the 4'-phosphopantetheinyl transferases (EntD homologues), there is little evidence to support this function.