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A unique Mycobacterium ESX-1 protein co-secretes with CFP-10/ESAT-6 and is necessary for inhibiting phagosome
Junjie Xu1, Olli Laine, Mark Masciocchi
1Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA.
Abstract:
The ESX-1 secretion system plays a critical role in the virulence of Mycobacterium tuberculosis and M. marinum. To date, three proteins are known to be secreted by ESX-1 and necessary for virulence, two of which are CFP-10 and ESAT-6. The ESX-1 secretion and the virulence mechanisms are not well understood. In this study, we have examined the M. marinum secretomes and identified four proteins specific to ESX-1. Two of those are CFP-10 and ESAT-6, and the other two are novel: MM1553 (homologous to Rv3483c) and Mh3881c (homologous to Rv3881c). We have shown that Mh3881c, CFP-10 and ESAT-6 are co-dependent for secretion. Mh3881c is being cleaved at close to the C-terminus during secretion, and the C-terminal portion is critical to the co-dependent secretion, the ESAT-6 cellular levels, and interaction with ESAT-6. The co-dependent secretion is required for M. marinum intracellular growth in macrophages, where the Mh3881c C-terminal portion plays a critical role. The role of the co-dependent secretion in intracellular growth correlates with its role in inhibiting phagosome maturation. Both the secretion and the virulence defects of the Mh3881c mutant are complemented by Mh3881c or its M. tuberculosis homologue Rv3881c, suggesting that in M. tuberculosis, Rv3881c has similar functions.
Insights
Researchers identified novel proteins secreted by the ESX-1 system in Mycobacterium marinum. These proteins, including Mh3881c, are crucial for bacterial virulence and intracellular growth by inhibiting phagosome maturation.
Area of Science:
- Microbiology
- Molecular Biology
- Pathogenesis
Background:
- The ESX-1 secretion system is vital for Mycobacterium tuberculosis and M. marinum virulence.
- CFP-10 and ESAT-6 are known ESX-1 secreted proteins essential for virulence.
- Mechanisms of ESX-1 secretion and virulence are not fully understood.
Purpose of the Study:
- To investigate the M. marinum secretome and identify novel ESX-1 substrates.
- To elucidate the role of identified proteins in M. marinum virulence and secretion.
- To understand the function of Mh3881c and its interaction with ESAT-6 and CFP-10.
Main Methods:
- Proteomic analysis of M. marinum secretomes.
- Identification and characterization of ESX-1 specific proteins.
- Genetic manipulation and complementation studies in M. marinum.
- Analysis of bacterial intracellular growth in macrophages.
- Assessment of phagosome maturation inhibition.
Main Results:
- Four ESX-1 specific proteins were identified in M. marinum, including novel proteins MM1553 and Mh3881c.
- Mh3881c, CFP-10, and ESAT-6 exhibit co-dependent secretion.
- The C-terminal portion of Mh3881c is critical for co-dependent secretion, ESAT-6 levels, and interaction.
- Co-dependent secretion is essential for M. marinum intracellular growth and inhibition of phagosome maturation.
- M. tuberculosis Rv3881c complements the secretion and virulence defects of M. marinum Mh3881c mutants.
Conclusions:
- Mh3881c is a novel ESX-1 secreted protein crucial for M. marinum virulence.
- Co-dependent secretion of Mh3881c, ESAT-6, and CFP-10 is essential for intracellular survival.
- The C-terminus of Mh3881c plays a key role in regulating secretion and virulence.
- Rv3881c in M. tuberculosis likely has similar functions to Mh3881c in M. marinum.
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