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Updated: Mar 8, 2026
Fluorescence Assays for the Study of Mycobacterium tuberculosis Interaction with the Immune Receptor SLAMF1
Published on: February 28, 2025
Diverse effects of mycobacterial proline-proline-glutamic acid proteins upon interaction with host macrophages
Lu Meng1, Jingfeng Tong2, Qinglan Wang2
1MOE & MOH Key Laboratory of Medical Molecular Virology, Institutes of Biomedical Sciences, Fudan University, Shanghai 200032, P. R. China.
Abstract:
The proline-proline-glutamic acid (PPE) family proteins are abundant only in pathogenic Mycobacteria, but their general functions are far from unveiled. To investigate their roles in how Mycobacterium tuberculosis (Mtb) resists killing by the host, 25 PPE recombinant Mycobacterium smegmatis strains that overexpress Mtb PPE proteins were constructed. During phagocytosis, a similar amount of intracellular bacteria was observed at 2 h post-infection (hpi) for 24 PPE recombinants, while a 50% reduction of entrance was observed for the PPE29 recombinant. In addition, we found that 20 ppe genes significantly influenced the survival of mycobacteria within macrophage cells. Mycobacterial survival was promoted by overexpression of 18 of these genes and inhibited by the other two. Highest survival was observed for the PPE27 recombinant. We also measured the levels of proinflammatory cytokines tumor necrosis factor-alpha and interleukin-6 secreted by macrophages. The overall effects varied among the different PPE recombinants. Moreover, we also found that various PPE recombinants exhibited increased resistance against oxidative, acidic and sodium dodecyl sulfate stresses that could be encountered in vivo. Together, our results indicate that PPE proteins play distinct roles in mycobacterial survival in macrophages. The findings described here broaden our understanding of mycobacterial pathogenicity.
Insights
Proline-proline-glutamic acid (PPE) proteins in Mycobacterium tuberculosis influence bacterial survival within host macrophages. Overexpression of these proteins affects mycobacterial resistance to host defenses and various stresses.
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- Proline-proline-glutamic acid (PPE) proteins are unique to pathogenic Mycobacteria.
- The functions of PPE proteins in host-pathogen interactions remain largely unknown.
Purpose of the Study:
- To investigate the role of Mycobacterium tuberculosis (Mtb) PPE proteins in resisting host-mediated killing.
- To understand how PPE proteins contribute to mycobacterial survival and pathogenicity.
Main Methods:
- Construction of 25 recombinant Mycobacterium smegmatis strains overexpressing Mtb PPE proteins.
- Assessment of bacterial entry into macrophages and intracellular survival.
- Measurement of cytokine secretion (TNF-α, IL-6) by macrophages.
- Evaluation of bacterial resistance to oxidative, acidic, and SDS stresses.
Main Results:
- Overexpression of 24 PPE genes did not affect bacterial entry, but PPE29 reduced entry by 50%.
- 20 PPE genes significantly influenced intracellular survival; 18 promoted it, while 2 inhibited it, with PPE27 showing the highest survival promotion.
- PPE protein overexpression conferred increased resistance to oxidative, acidic, and SDS stresses.
Conclusions:
- PPE proteins play diverse roles in mycobacterial survival within macrophages.
- These findings enhance the understanding of PPE protein functions and their contribution to Mtb pathogenicity.
