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

Abstract

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 -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 discovered 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.