Mechanistic insights into Mtb effector EspB-mediated mitochondrial membrane damage

Abstract Mycobacterium tuberculosis ( Mtb ) utilises the ESX-1 type VII secretion system to export effector proteins, such as EspB, which ablate phagosome maturation, damage mitochondria, and lead to host-cell death. EspB assembles a heptameric oligomer under acidic and lipid-rich conditions. It interacts with mitochondrial lipids, mainly phosphatidic acid (PA), phosphatidylethanolamine (PE), and phosphatidylserine (PS) via its C-terminal region. However, the precise molecular mechanism remains unknown. Our current study demonstrates that EspB targets host mitochondria by coordinating interactions with both mitochondrial lipid and outer membrane protein Tom70. Biophysical, biochemical, and single-particle cryo-EM analyses revealed the structural architecture of the EspB-Tom70 complex, identifying key residues at the interaction interface. A mutagenesis study reveals that disruption of EspB-Tom70 complex formation reduces cellular cytotoxicity and mitochondrial damage in cellular assays, establishing a functional role for this interaction during infection. Together, these findings elucidate how Mtb hijacks host mitochondrial machinery through EspB to drive host-cell death during infection.