Mycobacterium tuberculosis lipoprotein LprG binds lipoarabinomannan and determines its cell envelope localization to control phagolysosomal fusion

LppM impact on the colonization of macrophages by Mycobacterium tuberculosis

Mycobacterium tuberculosis produces several bacterial effectors impacting the colonization of phagocytes. Here, we report that the putative lipoprotein LppM hinders phagocytosis by macrophages in a toll-like receptor 2-dependent manner. Moreover, recombinant LppM is able to functionally complement the phenotype of the mutant, when exogenously added during macrophage infection. LppM is also implicated in the phagosomal maturation, as a lppM deletion mutant is more easily addressed towards the acidified compartments of the macrophage than its isogenic parental strain. In addition, this mutant was affected in its ability to induce the secretion of pro-inflammatory chemokines, interferon-gamma-inducible protein-10, monocyte chemoattractant protein-1 and macrophage inflammatory protein-1α. Thus, our results describe a new mycobacterial protein involved in the early trafficking of the tubercle bacillus and its manipulation of the host immune response.

The mycobacterial P55 efflux pump is required for optimal growth on cholesterol

Cholesterol catabolism is thought to be a key factor contributing to the pathogenesis of Mycobacterium tuberculosis. Previous epistasis and mutant screening studies predicted that the P55 efflux pump (Rv1410c) positively interacts with the Mce4 transporter, a major cholesterol import system of M. tuberculosis and is needed for optimal growth in vitro, in macrophages, and in vivo. Using a combination of cell growth kinetic techniques, cholesterol consumption, and [4-(14)C]cholesterol uptake studies, we demonstrated that the Mycobacterium bovis BCG rv1410c gene indeed is needed for optimal in vitro growth on cholesterol and other carbon sources. Our data, together with previous predictions, support hypotheses that the P55 efflux pump functions in maintaining general metabolism or as a subunit of the Mce4 transport apparatus (catalyzing its assembly or providing cell wall integrity) to allow more efficient cholesterol uptake.

Comparative Genomic Analysis Reveals a Possible Novel Non-Tuberculous Mycobacterium Species with High Pathogenic Potential

Mycobacteria have been reported to cause a wide range of human diseases. We present the first whole-genome study of a Non-Tuberculous Mycobacterium, Mycobacterium sp. UM_CSW (referred to hereafter as UM_CSW), isolated from a patient diagnosed with bronchiectasis. Our data suggest that this clinical isolate is likely a novel mycobacterial species, supported by clear evidence from molecular phylogenetic, comparative genomic, ANI and AAI analyses. UM_CSW is closely related to the Mycobacterium avium complex. While it has characteristic features of an environmental bacterium, it also shows a high pathogenic potential with the presence of a wide variety of putative genes related to bacterial virulence and shares very similar pathogenomic profiles with the known pathogenic mycobacterial species. Thus, we conclude that this possible novel Mycobacterium species should be tightly monitored for its possible causative role in human infections.

Mycobacterium tuberculosis Peptidyl-Prolyl Isomerases Also Exhibit Chaperone like Activity In-Vitro and In-Vivo

Peptidyl-prolyl cis-trans isomerases (Ppiases), also known as cyclophilins, are ubiquitously expressed enzymes that assist in protein folding by isomerization of peptide bonds preceding prolyl residues. Mycobacterium tuberculosis (M.tb) is known to possess two Ppiases, PpiA and PpiB. However, our understanding about the biological significance of mycobacterial Ppiases with respect to their pleiotropic roles in responding to stress conditions inside the macrophages is restricted. This study describes chaperone-like activity of mycobacterial Ppiases. We show that recombinant rPpiA and rPpiB can bind to non-native proteins in vitro and can prevent their aggregation. Purified rPpiA and rPpiB exist in oligomeric form as evident from gel filtration chromatography.E. coli cells overexpressing PpiA and PpiB of M.tb could survive thermal stress as compared to plasmid vector control. HEK293T cells transiently expressing M.tb PpiA and PpiB proteins show increased survival as compared to control cells in response to oxidative stress and hypoxic conditions generated after treatment with H₂O₂ and CoCl₂ thereby pointing to their likely role in adaption under host generated oxidative stress and conditions of hypoxia. The chaperone-like function of these M.tuberculosis cyclophilins may possibly function as a stress responder and consequently contribute to virulence.

Mycobacterium tuberculosis: Manipulator of Protective Immunity

Mycobacterium tuberculosis (MTB) is one of the most successful pathogens in human history and remains a global health challenge. MTB has evolved a plethora of strategies to evade the immune response sufficiently to survive within the macrophage in a bacterial-immunological equilibrium, yet causes sufficient immunopathology to facilitate its transmission. This review highlights MTB as the driver of disease pathogenesis and presents evidence of the mechanisms by which MTB manipulates the protective immune response into a pathological productive infection.

Mycobacterial Metabolic Syndrome: LprG and Rv1410 Regulate Triacylglyceride Levels, Growth Rate and Virulence in Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) mutants lacking rv1411c, which encodes the lipoprotein LprG, and rv1410c, which encodes a putative efflux pump, are dramatically attenuated for growth in mice. Here we show that loss of LprG-Rv1410 in Mtb leads to intracellular triacylglyceride (TAG) accumulation, and overexpression of the locus increases the levels of TAG in the culture medium, demonstrating a role of this locus in TAG transport. LprG binds TAG within a large hydrophobic cleft and is sufficient to transfer TAG from donor to acceptor membranes. Further, LprG-Rv1410 is critical for broadly regulating bacterial growth and metabolism in vitro during carbon restriction and in vivo during infection of mice. The growth defect in mice is due to disrupted bacterial metabolism and occurs independently of key immune regulators. The in vivo essentiality of this locus suggests that this export system and other regulators of metabolism should be considered as targets for novel therapeutics.

Of the estimated 2 billion people worldwide currently infected with Mycobacterium tuberculosis (Mtb), surprisingly few go on to develop active tuberculosis (TB) disease. The vast majority, 95 percent, of infected individuals develop latent TB, remaining infected but without disease. Despite its importance in global health, the question of what determines whether an infected individual will develop active or latent TB remains largely unanswered. Changes in how Mtb grows in response to stressors presented by the host environment likely play an important role in this process. In particular, the manifold ways in which Mtb synthesizes, degrades, and transports lipids dictates its growth in an infected host. Here, we show that lipid transport is an important function of two TB genes known to be required for Mtb’s ability to cause disease in the mouse model of infection. Using a variety of genetic and biochemical techniques, we found that the products of these genes prevent the cytosolic accumulation of a lipid associated with non-growing Mtb under the metabolic conditions it encounters during infection. Our results indicate an important role for the metabolism of Mtb in its ability to orchestrate a productive infection and cause disease.

Manipulation of the endocytic pathway and phagocyte functions by Mycobacterium tuberculosis lipoarabinomannan

Lipoarabinomannan is a major immunomodulatory lipoglycan found in the cell envelope of Mycobacterium tuberculosis and related human pathogens. It reproduces several salient properties of M. tuberculosis in phagocytic cells, including inhibition of pro-inflammatory cytokine production, inhibition of phagolysosome biogenesis, and inhibition of apoptosis as well as autophagy. In this review, we present our current knowledge on lipoarabinomannan structure and ability to manipulate the endocytic pathway as well as phagocyte functions. A special focus is put on the molecular mechanisms employed and the signaling pathways hijacked. Available information is discussed in the context of M. tuberculosis pathogenesis.