Chlamydia trachomatis invasion: a duet of effectors

Members of the genus Chlamydia require an intracellular niche for growth and replication, thus highlighting the extreme significance of its ability to invade epithelial cells—the favored host cell in vivo. Because epithelial cells are not phagocytic, the uptake of Chlamydia must be driven by the pathogen. To this end, two bacterial proteins, translocated actin-recruiting protein (TarP) and translocated membrane effector A (TmeA), identified in Chlamydia trachomatis are translocated from the infectious chlamydial elementary bodies to the host cell cytosol to facilitate extensive remodeling of the cortical actin network to produce protrusive structures designed for pathogen engulfment. Notably, both effectors act by promoting highly localized actin nucleation at sites of bacterial adhesion. However, they have non-redundant functions, with both required for optimal actin remodeling dynamics and efficient invasion. Finally, these effectors also mediate the latter stages of the invasion process, specifically by modulating host dynamin 2, a large GTPase critical to closure and scission of invaginating vesicles harboring elementary bodies. In summary, TarP and TmeA orchestrate major aspects of C. trachomatis invasion.