Chlamydia trachomatis effector Tri1 interacts with TRAF7 to displace native TRAF7 interactors

Chlamydia trachomatis is the leading cause of bacterial sexually transmitted infections in the US and preventable blindness worldwide. This obligate intracellular pathogen replicates within a membrane-bound inclusion, but how it acquires nutrients from the host while avoiding detection by the innate immune system is incompletely understood. Chlamydia accomplishes this in part through the translocation of a unique set of effectors into the inclusion membrane, the inclusion membrane proteins (Incs). Incs are ideally poised at the host-pathogen interface to reprogram host signaling by redirecting proteins or organelles to the inclusion. Using a combination of co-affinity purification, immunofluorescence confocal imaging, and proteomics, we characterize the interaction between an early-expressed Inc of unknown function, Tri1, and tumor necrosis factor receptor associated factor 7 (TRAF7). TRAF7 is a multi-domain protein with a RING finger ubiquitin ligase domain and a C-terminal WD40 domain, the latter is mutated in a subset of tumors. TRAF7 regulates several innate immune signaling pathways associated with C. trachomatis infection. We demonstrate that Tri1 and TRAF7 specifically interact during infection and that TRAF7 is recruited to the inclusion. We further show that the predicted coiled-coil domain Tri1 is necessary and sufficient to interact with the TRAF7 WD40 domain. Finally, we demonstrate that Tri1 displaces native TRAF7 binding partners, MEKK2 and MEKK3. Together, our results suggest that by displacing the TRAF7 native binding partners MEKK2 and/or MEKK3, Tri1 has the capacity to alter TRAF7 signaling during infection.