The type III secretion system (T3SS) is a complex nanomachine used by numerous Gram-negative bacteria to inject toxins directly into target cells. Its architecture resembles a syringe, and toxins are believe to travel through its interior. One key aspect of the T3SS is the translocon, a complex of two membrane proteins that are synthesized within the bacterial cytoplasm, transported through the interior of the needle, and subsequently inserted directly into the membrane of the eukaryotic cell, allowing toxin passage.

In this work IBS scientists and their collaborators from BIG and London Imperial College showed that insertion of the translocon proteins (PopB and PopD) by the human pathogen Pseudomonas aeruginosa into target membranes engenders epigenetic modifications on histone H3 as a consequence of ion exchange through the formed pore. This thus indicates, for the first time, that the translocon acts not only as a pore, but also as a real virulence factor.