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Updated: Nov 21, 2025

Preparation of Mycobacterium Tuberculosis Culture Filtrate to Understand TB Pathogenesis
Published on: March 28, 2025
Pore-forming Esx proteins mediate toxin secretion by Mycobacterium tuberculosis
Uday Tak1, Terje Dokland1, Michael Niederweis2
1Department of Microbiology, University of Alabama at Birmingham, 845 19th Street South, Birmingham, AL, 35294, USA.
Abstract:
Mycobacterium tuberculosis secretes the tuberculosis necrotizing toxin (TNT) to kill host cells. Here, we show that the WXG100 proteins EsxE and EsxF are essential for TNT secretion. EsxE and EsxF form a water-soluble heterodimer (EsxEF) that assembles into oligomers and long filaments, binds to membranes, and forms stable membrane-spanning channels. Electron microscopy of EsxEF reveals mainly pentameric structures with a central pore. Mutations of both WXG motifs and of a GXW motif do not affect dimerization, but abolish pore formation, membrane deformation and TNT secretion. The WXG/GXW mutants are locked in conformations with altered thermostability and solvent exposure, indicating that the WXG/GXW motifs are molecular switches controlling membrane interaction and pore formation. EsxF is accessible on the bacterial cell surface, suggesting that EsxEF form an outer membrane channel for toxin export. Thus, our study reveals a protein secretion mechanism in bacteria that relies on pore formation by small WXG proteins.
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