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Specific chaperones for the type VII protein secretion pathway.

Maria H Daleke¹, Aniek D van der Woude, Annabel H A Parret

¹Department of Medical Microbiology and Infection Control, VU University Medical Center, 1081 BT Amsterdam, The Netherlands.

The Journal of Biological Chemistry

|July 31, 2012

Summary

Mycobacterium secretion systems ESX-1 and ESX-5 utilize specific EspG chaperones to deliver PE/PPE virulence factors. EspG(5) and EspG(1) proteins bind only to PE/PPE substrates secreted by their respective ESX pathways.

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Area of Science:

Microbiology
Molecular Biology
Protein Secretion

Background:

Mycobacteria employ type VII secretion systems (ESX-1 and ESX-5) to export virulence factors, including PE and PPE proteins, across their hydrophobic cell envelope.
The precise mechanisms by which ESX-1 and ESX-5 recognize their specific PE/PPE substrates remain largely unknown.

Purpose of the Study:

To investigate the function of the cytosolic protein EspG(5) in ESX-5-mediated secretion in Mycobacterium marinum.
To determine if EspG proteins act as specific recognition factors or chaperones for PE/PPE substrates within the ESX pathways.

Main Methods:

Protein co-purification assays to identify interactions between EspG proteins and PE/PPE substrates.
Comparative analysis of EspG(5) and its ESX-1 paralogue, EspG(1), with substrates of both ESX-5 and ESX-1 pathways.
Structural analysis of the EspG(5)-PE/PPE complex.

Main Results:

EspG(5) specifically interacts with PE/PPE proteins secreted by ESX-5, but not with ESX-1 substrates or unrelated ESX-5 substrates.
EspG(1) interacts with PE/PPE proteins secreted by ESX-1, but not with ESX-5 substrates.
Structural analysis revealed a 1:1:1 interaction ratio between EspG(5) and its PE/PPE partners.

Conclusions:

EspG(5) and EspG(1) exhibit specificity for PE/PPE proteins secreted via their cognate ESX systems.
The EspG proteins function as specific chaperones, mediating the recognition and secretion of PE/PPE substrates by type VII secretion pathways.