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Proc Natl Acad Sci U S A. 2016 Jan 19;113(3):E348-57. doi: 10.1073/pnas.1523321113. Epub 2016 Jan 4.

Separable roles for Mycobacterium tuberculosis ESX-3 effectors in iron acquisition and virulence.

Author information

1
Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461; Department of Medicine, Albert Einstein College of Medicine, Bronx, NY 10461;
2
Office of Collaborative Science, New York University School of Medicine, New York, NY 10016;
3
Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461;
4
Shanghai Public Health Clinical Center, Key Laboratory of Medical Molecular Virology of the Ministry of Education/Health, School of Basic Medical Sciences, Fudan University, Shanghai 201508, China;
5
Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461; Howard Hughes Medical Institute, Albert Einstein College of Medicine, Bronx, NY 10461;
6
Department of Microbiology, University of Alabama at Birmingham, Birmingham, AL 35294;
7
Division of Infectious Diseases, Department of Medicine, New York University School of Medicine, New York, NY 10016;
8
Laboratory of Computational Proteomics, Center for Health Informatics and Bioinformatics, New York University School of Medicine, New York, NY 10016; Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016.
9
Office of Collaborative Science, New York University School of Medicine, New York, NY 10016; Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016.
10
Division of Infectious Diseases, Department of Medicine, New York University School of Medicine, New York, NY 10016; jphilips@dom.wustl.edu jacobsw@hhmi.org.
11
Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461; Howard Hughes Medical Institute, Albert Einstein College of Medicine, Bronx, NY 10461; jphilips@dom.wustl.edu jacobsw@hhmi.org.

Abstract

Mycobacterium tuberculosis (Mtb) encodes five type VII secretion systems (T7SS), designated ESX-1-ESX-5, that are critical for growth and pathogenesis. The best characterized is ESX-1, which profoundly impacts host cell interactions. In contrast, the ESX-3 T7SS is implicated in metal homeostasis, but efforts to define its function have been limited by an inability to recover deletion mutants. We overcame this impediment using medium supplemented with various iron complexes to recover mutants with deletions encompassing select genes within esx-3 or the entire operon. The esx-3 mutants were defective in uptake of siderophore-bound iron and dramatically accumulated cell-associated mycobactin siderophores. Proteomic analyses of culture filtrate revealed that secretion of EsxG and EsxH was codependent and that EsxG-EsxH also facilitated secretion of several members of the proline-glutamic acid (PE) and proline-proline-glutamic acid (PPE) protein families (named for conserved PE and PPE N-terminal motifs). Substrates that depended on EsxG-EsxH for secretion included PE5, encoded within the esx-3 locus, and the evolutionarily related PE15-PPE20 encoded outside the esx-3 locus. In vivo characterization of the mutants unexpectedly showed that the ESX-3 secretion system plays both iron-dependent and -independent roles in Mtb pathogenesis. PE5-PPE4 was found to be critical for the siderophore-mediated iron-acquisition functions of ESX-3. The importance of this iron-acquisition function was dependent upon host genotype, suggesting a role for ESX-3 secretion in counteracting host defense mechanisms that restrict iron availability. Further, we demonstrate that the ESX-3 T7SS secretes certain effectors that are important for iron uptake while additional secreted effectors modulate virulence in an iron-independent fashion.

KEYWORDS:

ESX-3; Mycobacterium tuberculosis; mycobactin; siderophore; type VII secretion system

PMID:
26729876
PMCID:
PMC4725510
DOI:
10.1073/pnas.1523321113
[Indexed for MEDLINE]
Free PMC Article

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