EspC forms a filamentous structure in the cell envelope of Mycobacterium tuberculosis and impacts ESX-1 secretion

July 28, 2017

Title

EspC forms a filamentous structure in the cell envelope of Mycobacterium tuberculosis and impacts ESX-1 secretion

Author

Ye Lou, Jan Rybniker, Claudia Sala, Stewart T. Cole

Year

2016

Journal

Molecular Microbiology

Abstract

Pathogenicity of Mycobacterium tuberculosis (M. tb) is mediated by the ESX-1 secretion system, which exports EsxA and EsxB, the major virulence factors that are co-secreted with EspA and EspC. Functional information about ESX-1 components is scarce. Here, we show that EspC associates with EspA in the cytoplasm and membrane, then polymerizes during secretion from M. tb. EspC was localized by immuno-gold electron microscopy in whole cells or cryo-sections as a surface-exposed filamentous structure that seems to span the cell envelope. Consistent with these findings, purified EspC homodimerizes via disulfide bond formation, multimerizes and self-assembles into long filaments in vitro. The C-terminal domain is required for multimerization as truncation and selected point mutations therein impact EspC filament formation, thus reducing secretion of EsxA and causing attenuation of M. tb. The data are consistent with EspC serving either as a modulator of ESX-1 function or as a component of the secretion apparatus.

Instrument

J-815

Keywords

Circular dichroism, Secondary structure, Polymers, Biochemistry