Transcriptional profile of Mycobacterium tuberculosis espL deletion mutant

The ESX-1, type VII, secretion system represents the major virulence determinant of Mycobacterium tuberculosis. The ESX-1 cluster comprises approximately twenty genes and encodes a specialized secretion apparatus, which releases effectors into the extracellular milieu. The goal of this study is to understand the role of EspL. We show that EspL, a protein of 115 amino acids, is essential for mediating ESX-1-dependent virulence and for stabilization of EspE, EspF and EspH protein levels. Indeed, an espL knock-out mutant was unable to replicate intracellularly, secrete ESX-1 substrates or stimulate innate cytokine production. Moreover, loss of EspL also leads to downregulation in M. tuberculosis of WhiB6, a redox-sensitive transcriptional activator of ESX-1 genes. delta espL vs. wild-type