Mycobacterial Esx-3 Requires Multiple Components for Iron Acquisition
Siegrist, M. Sloan
Dragset, Marte S.
Schuster, Brian M.
Philips, Jennifer A.
Carr, Steven A.
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CitationSiegrist, M. Sloan, Magnus Steigedal, Rushdy Ahmad, Alka Mehra, Marte S. Dragset, Brian M. Schuster, Jennifer A. Philips, Steven A. Carr, and Eric J. Rubin. 2014. “Mycobacterial Esx-3 Requires Multiple Components for Iron Acquisition.” mBio 5 (3): e01073-14. doi:10.1128/mBio.01073-14. http://dx.doi.org/10.1128/mBio.01073-14.
AbstractABSTRACT The type VII secretion systems are conserved across mycobacterial species and in many Gram-positive bacteria. While the well-characterized Esx-1 pathway is required for the virulence of pathogenic mycobacteria and conjugation in the model organism Mycobacterium smegmatis, Esx-3 contributes to mycobactin-mediated iron acquisition in these bacteria. Here we show that several Esx-3 components are individually required for function under low-iron conditions but that at least one, the membrane-bound protease MycP3 of M. smegmatis, is partially expendable. All of the esx-3 mutants tested, including the ΔmycP3ms mutant, failed to export the native Esx-3 substrates EsxHms and EsxGms to quantifiable levels, as determined by targeted mass spectrometry. Although we were able to restore low-iron growth to the esx-3 mutants by genetic complementation, we found a wide range of complementation levels for protein export. Indeed, minute quantities of extracellular EsxHms and EsxGms were sufficient for iron acquisition under our experimental conditions. The apparent separation of Esx-3 function in iron acquisition from robust EsxGms and EsxHms secretion in the ΔmycP3ms mutant and in some of the complemented esx-3 mutants compels reexamination of the structure-function relationships for type VII secretion systems.
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