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Mol Microbiol. 2012 Oct;86(2):472-84. doi: 10.1111/j.1365-2958.2012.08206.x. Epub 2012 Aug 27.

Composition of the type VII secretion system membrane complex.

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1
Department of Medical Microbiology and Infection Control, VU University Medical Center, Amsterdam, The Netherlands. e.houben@vumc.nl

Abstract

Pathogenic mycobacteria require type VII secretion (T7S) systems to transport virulence factors across their complex cell envelope. These bacteria have up to five of these systems, termed ESX-1 to ESX-5. Here, we show that ESX-5 of Mycobacterium tuberculosis mediates the secretion of EsxN, PPE and PE_PGRS proteins, indicating that ESX-5 is a major secretion pathway in this important pathogen. Using the ESX-5 system of Mycobacterium marinum and Mycobacterium bovis BCG as a model, we have purified and analysed the T7S membrane complex under native conditions. blue native-PAGE and immunoprecipitation experiments showed that the ESX-5 membrane complex of both species has a size of ~ 1500 kDa and is composed of four conserved membrane proteins, i.e. EccB(5) , EccC(5) , EccD(5) and EccE(5) . Subsequent limited proteolysis suggests that EccC(5) and EccE(5) mostly reside on the periphery of the complex. We also observed that EccC(5) and EccD(5) expression is essential for the formation of a stable membrane complex. These are the first data on a T7S membrane complex and, given the high conservation of its components, our data can likely be generalized to most mycobacterial T7S systems.

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