Protein export via the accessory SecA2 system of Mycobacterium tuberculosis

The SecA2 protein export system is critical for the virulence of Mycobacterium tuberculosis. However, the mechanism of this export pathway remains unclear. Through a screen for suppressors of a secA2 mutant, we identified a new player in the mycobacterial SecA2 pathway that we named SatS for SecA2 (two) Suppressor. In M. tuberculosis, SatS is required for the export of a subset of SecA2 substrates and for growth in macrophages. We further identify a role for SatS as a protein export chaperone. SatS exhibits multiple properties of a chaperone, including the ability to bind to and protect substrates from aggregation. Our structural studies of SatS reveal a distinct combination of a new fold and hydrophobic grooves resembling preprotein-binding sites of the SecB chaperone. These results are significant in better defining a molecular pathway for M. tuberculosis pathogenesis and in expanding our appreciation of the diversity among chaperones and protein export systems.

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The Mycobacterium tuberculosis SecA2 System Subverts Phagosome Maturation To Promote Growth in Macrophages

Infection and Immunity ◽

10.1128/iai.05987-11 ◽

2012 ◽

Vol 80 (3) ◽

pp. 996-1006 ◽

Cited By ~ 51

Author(s):

Jonathan Tabb Sullivan ◽

Ellen F. Young ◽

Jessica R. McCann ◽

Miriam Braunstein

Keyword(s):

Mycobacterium Tuberculosis ◽

Protein Export ◽

Growth Defect ◽

Phagosome Maturation ◽

Wild Type ◽

Intracellular Growth ◽

Maturation Arrest ◽

Content Type ◽

Late Endosomes ◽

Export System

The ability ofMycobacterium tuberculosisto grow in macrophages is critical to the virulence of this important pathogen. One wayM. tuberculosisis thought to maintain a hospitable niche in macrophages is by arresting the normal process of phagosomes maturing into acidified phagolysosomes. The process of phagosome maturation arrest byM. tuberculosisis not fully understood, and there has remained a need to firmly establish a requirement for phagosome maturation arrest forM. tuberculosisgrowth in macrophages. Other intracellular pathogens that control the phagosomal environment use specialized protein export systems to deliver effectors of phagosome trafficking to the host cell. InM. tuberculosis, the accessory SecA2 system is a specialized protein export system that is required for intracellular growth in macrophages. In studying the importance of the SecA2 system in macrophages, we discovered that SecA2 is required for phagosome maturation arrest. Shortly after infection, phagosomes containing a ΔsecA2mutant ofM. tuberculosiswere more acidified and showed greater association with markers of late endosomes than phagosomes containing wild-typeM. tuberculosis. We further showed that inhibitors of phagosome acidification rescued the intracellular growth defect of the ΔsecA2mutant, which demonstrated that the phagosome maturation arrest defect of the ΔsecA2mutant is responsible for the intracellular growth defect. This study demonstrates the importance of phagosome maturation arrest forM. tuberculosisgrowth in macrophages, and it suggests there are effectors of phagosome maturation that are exported into the host environment by the accessory SecA2 system.

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Directed evolution of SecB chaperones toward toxin-antitoxin systems

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1710456114 ◽

2017 ◽

Vol 114 (47) ◽

pp. 12584-12589 ◽

Cited By ~ 6

Author(s):

Ambre Julie Sala ◽

Patricia Bordes ◽

Sara Ayala ◽

Nawel Slama ◽

Samuel Tranier ◽

...

Keyword(s):

Escherichia Coli ◽

Mycobacterium Tuberculosis ◽

Directed Evolution ◽

Substrate Binding ◽

Family Members ◽

Protein Export ◽

Adaptation To Stress ◽

Bacterial Adaptation ◽

Chaperone Function ◽

Binding Surface

SecB chaperones assist protein export in bacteria. However, certain SecB family members have diverged to become specialized toward the control of toxin-antitoxin (TA) systems known to promote bacterial adaptation to stress and persistence. In such tripartite TA-chaperone (TAC) systems, the chaperone was shown to assist folding and to prevent degradation of its cognate antitoxin, thus facilitating inhibition of the toxin. Here, we used both the export chaperone SecB ofEscherichia coliand the tripartite TAC system ofMycobacterium tuberculosisas a model to investigate how generic chaperones can specialize toward the control of TA systems. Through directed evolution of SecB, we have identified and characterized mutations that specifically improve the ability of SecB to control our model TA system without affecting its function in protein export. Such a remarkable plasticity of SecB chaperone function suggests that its substrate binding surface can be readily remodeled to accommodate specific clients.

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