Polarly localized EccE ₁ is required for ESX-1 function and stabilization of ESX-1 membrane proteins in <i>Mycobacterium tuberculosis</i>

ABSTRACT Mycobacterium tuberculosis is a slow-growing intracellular bacterium with the ability to induce host cell death and persist indefinitely in the human body. This pathogen uses the specialized ESX-1 secretion system to secrete virulence factors and potent immunogenic effectors required for disease progression. ESX-1 is a multi-subunit apparatus with a membrane complex that is predicted to form a pore in the cytoplasmic membrane. In M. tuberculosis this complex is composed of five membrane proteins: EccB 1 , EccCa 1 , EccCb 1 , EccD 1 , EccE 1 . In this study, we have characterized the membrane component EccE 1 and found that deletion of eccE 1 lowers the levels of EccB 1 , EccCa 1 and EccD 1 thereby abolishing ESX-1 secretion and attenuating M. tuberculosis ex vivo . Surprisingly, secretion of EspB was not affected by loss of EccE 1 . Furthermore, EccE 1 was found to be a membrane- and cell-wall associated protein that needs the presence of other ESX-1 components to assemble into a stable complex at the poles of M. tuberculosis . Overall, this investigation provides new insights into the role of EccE 1 and its localization in M. tuberculosis . IMPORTANCE Tuberculosis (TB), the world’s leading cause of death of humans from an infectious disease, is caused by the intracellular bacterium Mycobacterium tuberculosis . The development of successful strategies to control TB requires better understanding of the complex interactions between the pathogen and human host. We investigated the contribution of EccE 1 , a membrane protein, to the function of the ESX-1 secretion system, the major virulence determinant of M. tuberculosis . By combining genetic analysis of selected mutants with eukaryotic cell biology and proteomics, we demonstrate that EccE 1 is critical for ESX-1 function, secretion of effector proteins and pathogenesis. Our research improves knowledge of the molecular basis of M. tuberculosis virulence and enhances our understanding of pathogenesis.