title: Specific chaperones for the type VII protein secretion pathway.
abstract: Mycobacteria use the dedicated type VII protein secretion systems ESX-1 and ESX-5 to secrete virulence factors across their highly hydrophobic cell envelope. The substrates of these systems include the large mycobacterial PE and PPE protein families, which are named after their characteristic Pro-Glu and Pro-Pro-Glu motifs. Pathogenic mycobacteria secrete large numbers of PE/PPE proteins via the major export pathway, ESX-5. In addition, a few PE/PPE proteins have been shown to be exported by ESX-1. It is not known how ESX-1 and ESX-5 recognize their cognate PE/PPE substrates. In this work, we investigated the function of the cytosolic protein EspG(5), which is essential for ESX-5-mediated secretion in Mycobacterium marinum, but for which the role in secretion is not known. By performing protein co-purifications, we show that EspG(5) interacts with several PPE proteins and a PE/PPE complex that is secreted by ESX-5, but not with the unrelated ESX-5 substrate EsxN or with PE/PPE proteins secreted by ESX-1. Conversely, the ESX-1 paralogue EspG(1) interacted with a PE/PPE couple secreted by ESX-1, but not with PE/PPE substrates of ESX-5. Furthermore, structural analysis of the complex formed by EspG(5) and PE/PPE indicates that these proteins interact in a 1:1:1 ratio. In conclusion, our study shows that EspG(5) and EspG(1) interact specifically with PE/PPE proteins that are secreted via their own ESX systems and suggests that EspG proteins are specific chaperones for the type VII pathway.
authors: Department of Medical Microbiology and Infection Control, VU University Medical Center, 1081 BT Amsterdam, The Netherlands.
authors: Maria H
authors: MH
authors: Daleke
authors: Aniek D
authors: AD
authors: van der Woude
authors: Annabel H A
authors: AH
authors: Parret
authors: Roy
authors: R
authors: Ummels
authors: A Marit
authors: AM
authors: de Groot
authors: David
authors: D
authors: Watson
authors: Sander R
authors: SR
authors: Piersma
authors: Connie R
authors: CR
authors: Jiménez
authors: Joen
authors: J
authors: Luirink
authors: Wilbert
authors: W
authors: Bitter
authors: Edith N G
authors: EN
authors: Houben
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D003001:Cloning, Molecular; D003600:Cytosol / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D005816:Genetic Complementation Test; D013058:Mass Spectrometry / Q000379:methods; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism; D019910:Mycobacterium marinum / Q000201:enzymology* / Q000378:metabolism; D009532:Nickel / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D055571:Secretory Pathway; D053719:Tandem Mass Spectrometry / Q000379:methods
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C429282:EspG protein, E coli; D018832:Molecular Chaperones; D009532:Nickel