Mycobacterium tuberculosis Resists Stress by Regulating PE19 Expression

Abstract

cMycobacterium tuberculosis requires the phosphate-sensing signal transduction system Pst/SenX3-RegX3 to resist host immune responses. A ⌬pstA1 mutant lacking a Pst phosphate uptake system component is hypersensitive to diverse stress conditions in vitro and is attenuated in vivo due to constitutive expression of the phosphate starvation-responsive RegX3 regulon. Transcriptional profiling of the ⌬pstA1 mutant revealed aberrant expression of certain pe and ppe genes. PE and PPE proteins, defined by conserved N-terminal domains containing Pro-Glu (PE) or Pro-Pro-Glu (PPE) motifs, account for a substantial fraction of the M. tuberculosis genome coding capacity, but their functions are largely uncharacterized. Because some PE and PPE proteins localize to the cell wall, we hypothesized that overexpression of these proteins sensitizes M. tuberculosis to stress by altering cell wall integrity. To test this idea, we deleted pe and ppe genes that were overexpressed by ⌬pstA1 bacteria. Deletion of a single pe gene, pe19, suppressed hypersensitivity of the ⌬pstA1 mutant to both detergent and reactive oxygen species. Ethidium bromide uptake assays revealed increased envelope permeability of the ⌬pstA1 mutant that was dependent on PE19. The replication defect of the ⌬pstA1 mutant in NOS2 ؊/؊ mice was partially reversed by deletion of pe19, suggesting that increased membrane permeability due to PE19 overexpression sensitizes M. tuberculosis to host immunity. Our data indicate that PE19, which comprises only a 99-amino-acid PE domain, has a unique role in the permeability of the M. tuberculosis envelope that is regulated to resist stresses encountered in the host. O ver 15 years ago, the novel PE and PPE protein families were identified in the complete genome sequence of Mycobacterium tuberculosis; together, these proteins represent over 7% of the genome coding capacity (1). Despite the attention placed on these protein families, their functions remain largely uncharacterized. PE and PPE proteins are defined by conserved N-terminal domains of ϳ110 or ϳ180 amino acids that contain Pro-Glu (PE) or Pro-Pro-Glu (PPE) sequence motifs, respectively (1). Although PE and PPE proteins can be identified in the genomes of all sequenced members of the Mycobacterium genus, their expansion into large multiprotein families is restricted to the slow-growing pathogenic mycobacterial species, including M. tuberculosis, and associated with the expansion of the ESX type VII secretion systems (2). There is evidence that some PE and PPE proteins are exported to the bacterial cell surface or extracellular milieu in an ESX-dependent manner (3-6). ESX-dependent export requires specific sequences within the PE or PPE domain (7, 8), including a recently described YxxxD/E ESX secretion targeting motif located near the C terminus of the ϳ110-amino-acid PE domain (9).The 99 PE proteins and 69 PPE proteins encoded by the M. tuberculosis H37Rv genome can be further divided into subfamilies based on C-terminal sequence motifs (2). The PE_PGRS (polymorphic GC-...

The Mycobacterium tuberculosis Phosphate-Sensing Pst/SenX3-RegX3 System Regulates ESX-5 Secretion to Evade Host Immunity

“…The Δ regX3 mutant failed to induce pe19, espG 5 or eccD 5 transcription in response to P i limitation, consistent with our previous reports (Fig. 3A) (14, 36). The Δ BS mutant similarly failed to induce pe19, espG 5 or eccD 5 transcription in response to P i limitation (Fig.…”

“…Irgm1 -/- mice were bred under specific-pathogen-free conditions at the University of Minnesota Research Animal Resources. Mice were infected with ∼100 CFU using an Inhalation Exposure System (GlasCol) as previously described (36). Infected mice were euthanized with CO 2 overdose.…”

Exploring the zoonotic potential of Mycobacterium bovis using variant calling approaches

“…Most of the PE PPE genes are localized to the cell wall for maintaining the cell wall integrity. It was also observed by Ramakrishnan et al, that the permeability issues created by the mutant pstsA1 gene could be replaced by deleting pe19 gene [61]. Hence, we hypothesize that the observed mutations pertaining to the cell wall and associated genes, like the several PE-PPE genes in NZ population may together contribute in modulating the M.bovis envelope to resist different stress conditions while infecting multiple hosts.…”

Esx Systems and the Mycobacterial Cell Envelope: What's the Connection?

“…The eccC 5 V762G mutation found in the clinical strains was sufficient to promote ofloxacin resistance when recapitulated in the M. tuberculosis H37Rv laboratory strain (143). While the mechanism linking ESX-5 to ofloxacin resistance is unknown (143), based on the studies presented above (58,141), mutation of an ESX-5 component could cause increased ofloxacin resistance by decreasing OM permeability and reducing the uptake of ofloxacin.…”

“…Although the precise substrates have yet to be identified, overexpression of the PE19 substrate in M. tuberculosis leads to increased membrane permeability (139,141).…”