Conformational Switch Driven Membrane Pore Formation by Mycobacterium Secretory Protein MPT63 Induces Macrophage Cell...

Area of Science:

• Microbiology
• Immunology
• Biochemistry

Background:

• Virulent Mycobacterium tuberculosis (MTB) strains induce macrophage (Mϕ) cell death within TB granulomas via poorly understood mechanisms.
• Bacterial toxins often facilitate infection by inducing host cell damage and promoting immune evasion, sometimes through environment-sensitive conformational changes.
• The existence and function of toxins in MTB remain largely unknown.

Purpose of the Study:

• To investigate the potential toxin-like behavior of the MTB-secreted protein MPT63.
• To elucidate the mechanism by which MPT63 might contribute to Mϕ cell death.

Main Methods:

• Investigated MPT63 conformational changes using fluorescence correlation spectroscopy and atomic force microscopy.
• Assessed MPT63's membrane interaction and pore-forming capabilities on synthetic and Mϕ membranes.
• Quantified Mϕ cell death using trypan blue exclusion and flow cytometry.

Main Results:

• MPT63 undergoes a conformational switch from β-sheet to helical structure under stress.
• The helical form of MPT63 forms pores in membranes and self-associates into toxic oligomers.
• MTB utilizes the helical MPT63 to induce Mϕ cell death.

Conclusions:

• MPT63 exhibits toxin-like activity through an environment-dependent conformational switch.
• Oligomerization of helical MPT63 leads to membrane pore formation and Mϕ lysis.
• This study reveals a novel mechanism of host cell manipulation by Mycobacterium tuberculosis.