Characterisation of the Bartonella quintana YopJ Homologue

Bartonella is a genus of re-emerging bacterial pathogens that typically cause asymptomatic, intra-erythrocytic bacteraemia in their reservoir hosts and are highly specialised to evade host immunity. One of the many mechanisms by which Bartonella spp. modulate the host immune system is the type-IV-secretion system, a protein complex that delivers effector proteins directly into host cells to modulate their function.

Some Bartonella species, including B. quintana, the causative agent of trench fever, possess an effector protein that is homologous to the effector YopJ of Yersinia species. Yersinia YopJ inhibits the MAPK and NF-kB pathways, and YopJ homologues in other species have similar effects, though through different targets. Very little is known about the function of the B. quintana YopJ homologue, but it may play a role in immune modulation by the bacteria.

My aim was to characterise the function of the B. quintana YopJ homologue.

I had evidence that it inhibits the NF-kB pathway, so I investigated which step of signalling activation is the target of this inhibition. I also sought to determine whether it impacts signalling pathways other than NF-kB, and to identify the specific host protein that it targets.

I performed these investigations using ELISA, high-throughput fluorescence microscopy, Western blotting, LC/MS proteomic screening, and a yeast two-hybrid screen.

I found that the B. quintana YopJ homologue inhibits the NF-kB pathway at or upstream of IKK activity, may also impact JNK signalling, the cell cycle, and the mTOR complex, and interacts with the host protein DCNL1, a component of neddylation machinery. Additionally, I determined that this interaction does not impact the neddylation of the protein Cullin-1.