Characterization of membrane interaction of Mycobacterium tuberculosis ESAT-6
Mycobacterium tuberculosis (Mtb) targets alveolar macrophages and has a high tolerance to the macrophage's antimicrobial effectors, such as low pH, reactive oxygen species, and reactive nitrogen species. It has been reported and widely accepted that Mtb disarms macrophages through arresting the normal maturation process of the phagosomes. Inhibition of phagosome-lysosome fusion and phagosome acidification is an effective survival strategy at the early stage of infection. This behavior allows Mtb to remain and replicate within the phagosomes of macrophages. At the later stage of infection, the pathogen translocates from the phagolysosomal compartments into the cytosol of host cells by phagolysosomal rupture. The main protein involved in virulence is known as MtbESAT-6, which is secreted by the ESX-1 secretion system and reportedly shows membrane-lysing properties. The ESX-1 secreting system is essential for the toxicity of MTB. The membrane interacting activity of MtbESAT-6 plays an important role during the infection. In this study, N- and C-terminal truncations and Cysteine mutations on the protein were generated to determine the role of N- and C-terminal flexible loops of MtbESAT-6 in membrane-interaction and the key membrane-interacting residues of MtbESAT-6. A series of fluorescence assays, including ANS, ANTS/DPX and Tryptophan, have demonstrated that both N- and C- terminal flexible loops were crucial for the membrane-interacting activity, suggesting a model that the loop area of the protein initiate the membrane attachment and the central helix-turn-helix inserts into the membranes. The study of ESX-1 secreting system, especially the molecular mechanism of MtbESAT-6 membrane interaction, is essential for us to understand how this virulence factor contributes to bacterial infection, and eventually will facilitate development of novel therapeutics against tuberculosis.
Ma, Yue, "Characterization of membrane interaction of Mycobacterium tuberculosis ESAT-6" (2014). ETD Collection for University of Texas, El Paso. AAI1557771.