Polarly Localized EccE(1) Is Required for ESX-1 Function and Stabilization of ESX-1 Membrane Proteins in Mycobacterium tuberculosis

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 multisubunit apparatus with a membrane complex that is predicted to form a channel in the cytoplasmic membrane. In M. tuberculosis this complex is composed of five membrane proteins: EccB(1), EccCa(1), EccCb(1), EccD(1), and 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.