Full-length structure of the host targeted bacterial effector Bep1 reveals a novel structural domain conserved in FIC effector proteins from Bartonella

Bacterial effector proteins translocated via a type-IV secretion system (T4SS) typically harbor a C-terminal segment required for recognition by the type-IV secretion coupling protein 1. In the alpha-proteobacterial pathogen Bartonella, the signal is bipartite being composed of a BID (Bep intracellular delivery) domain and a positively charged C-terminal tail 2. Here, we show the crystal structure of full length Bartonella effector protein 1 (Bep1), which shows a novel FIC-OB-BAS(BID) domain arrangement conserved in the majority of Beps with the BID domain inserted into the newly dis-covered BAS parent domain. We propose that the BAS domain is necessary for the overall boomerang-like shape of Bep1 and that it plays a role during translocation through the T4SS.